Pages 1--59 from Untitled

NEAR EARTH
OBJECTS 1
1Page 23
Cover (front and back)
SOLAR SYSTEM showing the Sun, the planets, the main
belt of asteroids and the orbit of a typical comet
(drawing not to scale). The planets are, counting from
the Sun: Mercury, Venus, Earth, Mars (to the left), the
giant planet Jupiter (to the right) and Saturn (top left,
back cover). The comet, coming from the far reaches of
the Solar System, is shown in two positions along its
orbit. The comet's tail always points directly away from
the Sun. The belt of asteroids contains about one million
objects over 1kilometre in size. Some asteroids are
deflected by Jupiter's gravitational field to become Near
Earth Objects. A stony asteroid is shown at the bottom
of the cover; it is covered with small craters by the
impact of other asteroids over the ages.

Title page
Moon impact craters (bottom) and Earth (top)
photographed from US Clementine spacecraft 1994.

Inside front and back covers
Asteroid and comet impact craters on far side of Moon. 2
2Page 34
Report of the Task Force on
potentially hazardous

Near Earth Objects

September 2000

NASA 3
3Page 45
List of Graphs, Tables
and Illustrations 4

Terms of Reference
and Membership of Task Force 5

Acknowledgements 5
Executive Summary 6
Summary of
Recommendations 7

Chapter 1
Introduction 9

Chapter 2
Asteroids, Comets
and Near Earth Objects 11

Chapter 3
Environmental Effects
on Earth 15

Chapter 4
Overall Risk 20

Chapter 5
Observational Techniques 22

Chapter 6
Current Activities
and Future Plans 24

Chapter 7
Activities in Britain 27

Chapter 8
Mitigation possibilities 28

Chapter 9
What is to be done?
including recommendations 30

Annex A
Chronology 36

Annex B
Impacts and Close
Approaches of Asteroids
and Comets 39

Annex C
Ground-based Telescopes
and Radars 43

Annex D
Space-based Missions 46

Glossary 49
Bibliography (and websites) 51
Acknowledgements
for Illustrations 54

CONTENTS

3 4
4Page 56
4
Graphs Numbers of near Earth asteroids by size
(Chapter 2)
Frequency of impacts of near Earth asteroids
by size (Chapter 3)

Tables Impact effects by size of Near Earth Object

(Chapter 3)
Estimated fatalities for wide variety of different
impact scenarios (Chapter 4)

Illustrations Solar System (Cover)

Asteroid and comet impact craters on Moon
(Inside front and back covers)

Moon craters and Earth (Title page)
Orbits of all known near Earth asteroids
(Chapter 1)

Barringer Crater, Arizona
(Chapter 1)

Asteroid Eros from orbiting spacecraft
(Chapter 2)

Orbits of asteroids Aten, Apollo and Amor
(Chapter 2)

Asteroid belt within Jupiter's orbit
(Chapter 2)

Comet Hale-Bopp above Stonehenge
(Chapter 2)

Orbits of Halley's comet and Hale-Bopp
(Chapter 2)

Sources of long and short period comets
(Chapter 2)

Comet Shoemaker-Levy 9 hitting Jupiter, 1994
(Chapter 3)

Asteroid and comet impact craters on Moon
(Chapter 3)

Tsunami from Eltanin impact,
South East Pacific
(Chapter 3)

Clearwater Lakes, Quebec, formed from twin
impact craters
(Chapter 3)

Asteroid seen by movement against fixed stars
(Chapter 5)

LINEAR Survey Telescope, New Mexico
(Chapter 6)

United Kingdom Schmidt Telescope, Australia
(Chapter 7)

NASA's Deep Impact mission to hit comet
(Chapter 8)

LIST OF GRAPHS, TABLES & ILLUSTRATIONS 5
5Page 67
5
On 4 January 2000 the Minister for Science, Lord
Sainsbury, announced the setting up of a Task Force
on Potentially Hazardous Near Earth Objects
(NEOs).
The Task Force was invited to make proposals to
the Government on how the United Kingdom
should best contribute to international effort on
Near Earth Objects; and to

1. confirm the nature of the hazard and potential
levels of risk;

2. identify the current UK contribution to
international efforts;

3. advise the Government on what further action

to take in the light of 1 and 2 above and on
the communication of issues to the public; and
to report to the Director General of the
British National Space Centre (BNSC) by the
middle of 2000.

The Task Force was chaired by Dr Harry Atkinson
with Sir Crispin Tickell and Professor David
Williams as members.
The British National Space Centre provided the
Secretary, Richard Tremayne-Smith, and general
support. The Task Force met on a number of
occasions and presented its Report to the Director
General of the British National Space Centre in
August 2000.

The Task Force has been supported by the British
National Space Centre; and has been helped greatly
by many people in the United Kingdom, in Europe,
the United States and in other countries. We cannot
hope to name them all.

However, our particular thanks go to the following
people who have made substantial contributions to
our understanding of the subject and in other ways:

Johannes Anderson, Mark Bailey, Andrea Carusi,
Alan Fitzsimmons, Tom Gehrels, Alan Harris,
Nigel Holloway, Brian Marsden, Tony Mayer,
David Morrison, Paul Murdin, Martin Rees,
Hans Richter, Jay Tate, Richard West, Iwan Williams,
Pete Worden, Don Yeomans; and a special thanks to
Duncan Steel for suggesting many of the illustrations
and in other ways.

In addition, the following have much helped us:
Michael A'Hearn, Morris Aizenman, David Asher,

Ben Atkinson, Jim Beletic, Andrea Boattini, Roger
Bonnet, Giacomo Cavallo, Catherine Cesarsky,
Moustafa Chahine, Andrew Cheng, Paul Chodas,
Victor Clube, Marcello Coradini, Ian Corbett, David
Crichton, Len Culhane, David Dale, Vernon J Ehlers,
Jim Emerson, Walter Flury, Bob Fosbury, Simon
French, Iain Gilmour, Monica Grady, Robert
Hawley, Eleanor Helin, Jeremy Hodge, Ken
Hodgkins, John Houghton, David Hughes, Julian
Hunt, Raymond Hyde, Syuzo Isobe, Lindley
Johnson, Adrian Jones, Patrick Laycock, Jean Le
Guen, Robert MacMillan, Vittorio Manno, Neil
McBride, Craig McKay, Duncan Moore, Patrick
Moore, Tom Morgan, Ian Morison, Richard
Oberman, Ron Oxburgh, Lembit Öpik, Vernon
Pankokin, Carl Pilcher, Klaus Pinkau, John Ponsonby,
Steven Pravdo, David Price, Antonio Rodotà,
Michael Schultz, John Schumacher, Geoff Sommers,
Hugh Van Horn, Victor Vilhard, Dan Weedman,
Chandra Wickramasinghe, John Zarnecki.

TERMS OF REFERENCE AND MEMBERSHIP OF TASK FORCE
ACKNOWLEDGEMENTS 6
6Page 78
6
E normous numbers of asteroids and comets orbit the Sun. Only a tiny fraction of them follow paths that bring them near the Earth. These Near Earth Objects range in size from pebbles to mountains, and travel at high speeds. Such objects have collided with the Earth since its formation, and brought the carbon and water which made life possible. They have also caused widespread changes in the Earth's surface, and occasional
extinctions of such living organisms as the dinosaurs.
The threat has only recently been recognised and
accepted. This has come about through advances in
telescope technology allowing the study of these
usually faint objects, the identification of craters on
the moon, other planets and the Earth as a result of
impacts, and the dramatic collision of pieces of the
comet Shoemaker-Levy 9 with Jupiter in 1994.
Impacts represent a significant risk to human and
other forms of life. Means now exist to mitigate the
consequences of such impacts for the human species.
The largest uncertainty in risk analysis arises from
our incomplete knowledge of asteroids whose orbits

bring them near to the Earth. With greater
information about them, fairly accurate predictions
can be made. The risk from comets is between 10
and 30 per cent of that from asteroids. The advance
warning period for a potential impact from a long
period comet may be as short as a year compared to
decades or centuries for asteroids. Short period
comets can be considered along with asteroids.
The threat from Near Earth Objects raises major
issues, among them the inadequacy of current
knowledge, confirmation of hazard after initial
observation, disaster management (if the worst
came to the worst), methods of mitigation
including deflection, and reliable communication
with the public. The Task Force believes that steps
should be taken at government level to set in place
appropriate bodies Ð international, European
including national Ð where these issues can be
discussed and decisions taken. The United
Kingdom is well placed to make a significant
contribution to what should be a global effort.
The recommendations of the Task Force are given
with supporting arguments in Chapter 9.

summary Executive EXECUTIVE SUMMARY 7
7Page 89
7
R ecommendations 1 to 9 cover the United Kingdom's scientific role within an international effort and Recommendations 10 to 14 the coordination of all aspects of the subject internationally, in Europe and in Britain. Survey and discovery of Near Earth Objects Recommendation 1
We recommend that the Government should seek
partners, preferably in Europe, to build in the
southern hemisphere an advanced new 3 metre-class
survey telescope for surveying substantially smaller
objects than those now systematically observed by
other telescopes. The telescope should be dedicated to
work on Near Earth Objects and be located on an
appropriate site.

Recommendation 2
We recommend that arrangements be made for
observational data obtained for other purposes by
wide-field facilities, such as the new British VISTA
telescope, to be searched for Near Earth Objects on a
nightly basis.

Recommendation 3
We recommend that the Government draw the
attention of the European Space Agency to the
particular role that GAIA, one of its future missions,
could play in surveying the sky for Near Earth
Objects. The potential in GAIA, and in other space
missions such as NASA's SIRTF and the European
Space Agency's BepiColombo, for Near Earth Object
research should be considered as a factor in defining
the missions and in scheduling their completion.

Accurate orbit
determination Recommendation 4

We recommend that the 1 metre Johannes Kapteyn
Telescope on La Palma, in which the United Kingdom
is a partner, be dedicated to follow-up observations
of Near Earth Objects.

Composition and
gross properties Recommendation 5

We recommend that negotiations take place with the
partners with whom the United Kingdom shares
suitable telescopes to establish an arrangement for
small amounts of time to be provided under
appropriate financial terms for spectroscopic follow-up
of Near Earth Objects.

Recommendation 6
We recommend that the Government explore, with
like-minded countries, the case for mounting a
number of coordinated space rendezvous missions
based on relatively inexpensive microsatellites, each to
visit a different type of Near Earth Object to establish
its detailed characteristics.

Coordination of
astronomical observations Recommendation 7

We recommend that the Government Ð together with
other governments, the International Astronomical
Union and other interested parties Ð seek ways of
putting the governance and funding of the Minor
Planet Center on a robust international footing,
including the Center's links to executive agencies if a
potential threat were found.

recommendations Summary of SUMMARY OF RECOMMENDATIONS 8
8Page 910
8
Studies of impacts and
environmental and social
effects Recommendation 8

We recommend that the Government should help
promote multi-disciplinary studies of the
consequences of impacts from Near Earth Objects on
the Earth in British and European institutions
concerned, including the Research Councils,
universities and the European Science Foundation.

Mitigation possibilities Recommendation 9
We recommend that the Government, with other
governments, set in hand studies to look into the
practical possibilities of mitigating the results of
impact and deflecting incoming objects.

Organisation
internationally Recommendation 10

We recommend that the Government urgently seek
with other governments and international bodies (in
particular the International Astronomical Union) to
establish a forum for open discussion of the scientific
aspects of Near Earth Objects, and a forum for
international action. Preferably these should be
brought together in an international body. It might
have some analogy with the Intergovernmental Panel
on Climate Change, thereby covering science,
impacts, and mitigation.

Organisation in Europe Recommendation 11
We recommend that the Government discuss with
like-minded European governments how Europe could
best contribute to international efforts to cope with
Near Earth Objects, coordinate activities in Europe,
and work towards becoming a partner with the
United States, with complementary roles in specific
areas. We recommend that the European Space
Agency and the European Southern Observatory, with
the European Union and the European Science
Foundation, work out a strategy for this purpose in
time for discussion at the ministerial meeting of the
European Space Agency in 2001.

Organisation
in United Kingdom Recommendation 12

We recommend that the Government appoint a single
department to take the lead for coordination and
conduct of policy on Near Earth Objects, supported
by the necessary inter-departmental machinery.

British National Centre
for Near Earth Objects Recommendation 13

We recommend that a British Centre for Near Earth
Objects be set up whose mission would be to promote
and coordinate work on the subject in Britain; to
provide an advisory service to the Government, other
relevant authorities, the public and the media, and to
facilitate British involvement in international
activities. In doing so it would call on the Research
Councils involved, in particular the Particle Physics
and Astronomy Research Council and the Natural
Environment Research Council, and on universities,
observatories and other bodies concerned in Britain.

Recommendation 14
We recommend that one of the most important
functions of a British Centre for Near Earth Objects be
to provide a public service which would give
balanced information in clear, direct and
comprehensible language as need might arise. Such a
service must respond to very different audiences: on
the one hand Parliament, the general public and the
media; and on the other the academic, scientific and
environmental communities. In all of this, full use
should be made of the Internet. As a first step, the
Task Force recommends that a feasibility study be
established to determine the functions, terms of
reference and funding for such a Centre. 9
9Page 1011
9
Introduction
T he Earth has been under a constant barrage of objects from space since its formation four and a half billion years ago. They cover a wide range, from the very small to the very big, with greatly different rates of arrival. Every day hundreds of tonnes of dust enter the upper atmosphere; every year objects of a few metres diameter do likewise, and some have effects on the ground; every century or so there are bigger impacts; and over long periods, stretching from hundreds of thousands to millions of years, objects with a diameter
of several kilometres hit the Earth with consequences
for life as a whole.
For long there was an unwillingness to recognise
that the Earth was not a closed system on
its own in space. The vast increase in
knowledge over the last half century has
shown otherwise. For example, it is now
widely accepted that the impact in
Yucatan caused the global changes
associated with the end of the long
dominance of the dinosaur family, some
65 million years ago. The huge Barringer
crater in Arizona, created some 49,000
years ago, was attributed to volcanic
action. Even the destruction of thousands
of square kilometres of forest in Siberia in
1908 was somehow brushed aside. An

equivalent impact on a city would eliminate it within
a diameter of about 40 kilometres, say the diameter of
London's ring road, the M25. Although over two-thirds
of the Earth is covered by water, and much of
the remainder is desert, mountain or ice-cap, traces of
many previous impacts can now be found.
This bombardment is integral to life on Earth. The
Earth was formed of the same material. Without
carbon and water there could be no life as we know it.
Periodic impacts have revised the conditions of
evolution, and shaped the course of the Earth's history.
As a species humans would not now exist without
them. On one hand we can rejoice in them; on the
other we can fear for our future.

INTRODUCTION

ORBITS OF ALL NEAR-EARTH ASTEROIDS known at
beginning of the year 2000, about 800 in all. The
orbits of the asteroids which cross the Earth's orbit
(Apollo-and Aten-types) are coloured yellow. They
are potentially dangerous. The others, the
"Amors", coloured red, approach the Earth but
cannot strike our planet. Also shown are the orbits
of Mars, Earth, Venus and Mercury, with the Sun
at the centre. The illustration shows that the Earth
is hemmed in by a sea of asteroids. The risk of
impacts is discussed in Chapter 4.

Scott Manley/ Armagh Observatory/ Duncan Steel (University of Salford)

Chap t e r 1 10
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10
Understanding of the threat from Near Earth
Objects Ð asteroids, long-and short-period comets Ð is
relatively new (see Chronology at Annex A). With
gathering evidence of past impacts, and a possible
analogy with the effects of nuclear war, the general
public as well as the astronomical and military
communities began to take a somewhat anxious
interest. The spectacle of the comet Shoemaker-Levy 9
colliding with the planet Jupiter in July 1994, throwing
up fire-balls as big as the Earth, and such films as
Armageddon and Deep Impact added to the concern.
Most practical work on the subject has so far been
done in the United States. The US Congress and the
US Administration through NASA and the
Department of Defense have promoted studies and
surveys, including the survey being done through a
NASA programme at the Lincoln Laboratory of the
Massachusetts Institute of Technology. Pioneering work
has been done at the Minor Planet Center at Boston.
At international level there has been interest in
the United Nations, particularly at successive UN
Conferences on the Exploration and Peaceful Uses
of Outer Space. The Council of Europe in
Strasbourg, the European Space Agency and many
other bodies have drawn attention to the hazards.
The same goes for the International Astronomical
Union, which brings together astronomers from all
over the world, and the Spaceguard Foundation set
up in Rome in 1996 with some national centres,
including Britain. These and other bodies organised
an important conference in Turin in June 1999,
when a scale for measuring the effects of impacts was

established. In Britain there has been interest
in both Houses of Parliament, and a debate
took place in the House of Commons on 3
March 1999.This was followed by the creation
of the present Task Force by the Minister for
Science in January 2000.
In the Report which follows, the Task
Force examines the nature of the asteroids and
comets which circulate within the Solar
System. We look at the facilities required to
identify the orbits and composition of those
coming near the Earth which range, in the
words of a distinguished American
astronomer, "from fluff ball ex-comets to
rubble piles, solid rocks and slabs of solid
iron", each with different consequences in the event
of terrestrial impact. We look at the effects of such
impacts, according to size and location. They include
blast, firestorms, intense acid rain, damage to the
ozone layer, injection of dust into the atmosphere,
tsunamis or giant ocean waves, and possible
vulcanism and earthquakes. We then assess the risks
and hazards of future impacts.
Building on the work already done, we consider
how a worldwide effort might be best organised and
coordinated, and what the British contribution
might be, both in national and international terms.
Here an element of particular importance is public
communication, which should be neither alarmist
nor complacent. Finally we look into the
fundamental problem of action in the event of an
emergency. Should we do as has been done in the
past, and simply let nature take its course? Should we
plan for civil defence, trying, for example, to cope
not only with direct hits but with such side effects as
tsunamis? Should we help promote technologies
which might destroy or deflect a Near Earth Object
on track for the Earth? If so what methods should be
used, and what would be the implications?
These and other issues are immensely difficult, and
the Task Force does not have all the answers. But it is
convinced that at a time when we understand better
than ever before the consequences for the world as a
whole, an international effort of research,
coordination and anticipatory measures is required in
which British science, technology and enterprise
should play an important part.

BARRINGER (OR METEOR) CRATER, Arizona, of diameter 1.2 kilometres
was created about 49,000 years ago by a small nickel-iron asteroid.
The crater's origin was for long controversial; eventually fragments of
the asteroid were identified together with the impact shock structure in
the impacted rocks and ejected material just outside the rim.

NASA 11
11Page 1213
and near-earth objects
11

Asteroids, comets
A steroids are sometimes called minor planets. Like the Earth and all the planets, asteroids move in orbits around the Sun, and so do comets. Asteroids and comets are remnants of the formation of the Solar System about 4.5 billion years ago. Asteroids were the building blocks of the inner planets; both they and comets delivered to Earth life's building blocks, carbon and water. Asteroids and comets can range in size from pebbles or lumps of ice, to rocky
or icy worlds nearly 1,000 kilometres across.
There are countless numbers of asteroids and
comets in the Solar System in well-defined regions
far from the Earth. The gravitational forces of the
large planets, mostly the huge planet Jupiter (which
comprises about 90 per cent of the combined mass
of all the planets), and collisions with other asteroids
or comets, slowly alter the orbits of these small
bodies.
Following many deflections, an asteroid or comet
may occasionally become a Near Earth Object, when
its orbit intersects that of the Earth or is within 0.3
Astronomical Units (astronomers call the Earth to
Sun distance one "Astronomical Unit" or 1 AU). It
may even crash onto the Earth. An object is said to
be potentially hazardous when its orbit comes even
closer to Earth, to within 0.05 AU (7.5 million
kilometres or about 20 times the Earth to Moon
distance) and when it is at least 150 metres in
diameter. So far, 258 potentially hazardous objects
have been discovered, a number that increases all the
time as the surveys continue. Given enough accurate
measurements of the position of an asteroid or
comet, astronomers can predict their paths over
centuries. But as they move about the Solar System,
they continue to suffer small deflections so that their

orbits are not wholly predictable far into the future.
Comets can sometimes be seen easily by the
naked eye when they are near the Sun, by their
bright tails. Asteroids are dark and generally smaller,
and are invisible to the naked eye; this is why not
even the biggest, Ceres (933 kilometres across), was
discovered until 1801. Astronomers are finding that
the distinction between comets and asteroids is
becoming increasingly blurred; but it is still
convenient to speak of them separately as we do
below.

Asteroids Most asteroids are in

orbits between those
of Mars and Jupiter,
two to four times
further from the Sun
than is the Earth (or
2 to 4 AU). This
main belt of
asteroids contains
about 1 million
objects over 1 kilo-metre
in diameter.
Unlike stars,
asteroids emit no
visible light. We can
only see them by the
Sun's reflected light
using a powerful
telescope; this is
because each asteroid
is very small and its
surface so dark that
it reflects only a

ASTEROIDS, COMETS AND NEAR-EARTH OBJECTS
ASTEROID EROS: Eros, shaped like a
potato, is about 33 kilometres long, 13
kilometres wide and 13 kilometres
thick. The crater at the top is 5.3
kilometres in diameter. Most known
near Earth asteroids are less than 1
kilometre across, much smaller than
Eros. This picture is a mosaic of six
photographs taken in February 2000
by NASA's NEAR spacecraft then
orbiting Eros at 200 kilometres above
its surface. The numerous impact
craters show that even asteroids are
hit by other asteroids many times in
their histories.

NEAR/ NASA

Chap t e r 2 12
12Page 1314
12
small percentage of the light falling on it. Usually
we see an asteroid only as a point source so that its
size cannot be directly determined. It is therefore
difficult to calculate the destructive power of an
asteroid if it were to impact on the Earth. We discuss
this problem further in Chapter 5.
Asteroids are made of carbonaceous (carbon
containing) materials, rocks (silicates) or metal. They
may comprise piles of boulders held together only
by their own very weak gravitational attraction, or
be solid lumps of stone or slabs of iron. They are not

spherical and may spin or tumble as they go. Stony
asteroids can have a density substantially less than
that of the material of which they are made,
indicating that they may sometimes be porous or
loosely packed. There are many sub-categories of
asteroids: each behaves differently when entering the
Earth's atmosphere, and in its reaction to
countermeasures.

Comets Many comets are in the Edgeworth-Kuiper Belt, a

region beyond Neptune, between 30 to 1,000 times
further from the Sun than the Earth. Perturbations

of comets at the inner edge of the Belt by giant
planets cause them to evolve out of the Belt giving
rise to so called short-period comets, with periods
of less than 200 years and orbits close to the plane
in which the planets move.
At the time of the formation of the giant planets,
much of the small icy debris from which they were
forming was ejected from the Solar System by the
powerful gravitational forces of the growing planets.
Some of these small bodies were almost but not
quite ejected and remain in very long orbits,
forming the so-called Oort cloud. The cloud
comprises billions of comets in a spherical shell
around the outer reaches of the Solar System, about
40 to 50 thousand times further away from the Sun
than the Earth or about one light-year, a quarter of
the way to our nearest star. The Oort cloud is the
source of long-period comets with return times
greater than 200 years.
The regions from which comets come are so cold
that they still contain frozen gases including water
vapour, methane, ammonia, carbon dioxide and
hydrogen cyanide. Comets are essentially "dirty
snow-balls" and include many particles of dust. It is
only when a comet comes near the Sun that these
gases evaporate, freeing the dust that forms the tail
sometimes seen by the naked eye. Using a powerful

ASTEROID BELT INSIDE JUPITER'S ORBIT. The belt
comprises about 1 million asteroids of diameter 1
kilometre and above; some asteroids are
occasionally deflected into orbits near the Earth's
orbit. Comets from much further out in the Solar
System are denoted by Sunward-pointing wedges.
Only objects from JPL's DASTCOM database are
used.

ORBITS OF ATEN, APOLLO AND AMOR, which gave
their names to the three main classes of near Earth
asteroid. The Aten and Apollo classes cross the
Earth's orbit; the Atens spend most of their time
between the Earth and Sun, making it difficult to
observe them with ground-based telescopes. Amors
are always outside the Earth's orbit and are therefore
not potentially dangerous.

NASA/ JPL
David
Asher 13
13Page 1415
13
telescope, it is possible to observe the tails of many
comets even at a distance of 5 AU from the
Sun. However, some comets have lost their
volatile gases and no longer generate tails; these
dead comets look much like asteroids and can
only be seen when near the Earth.
Short-period comets are likely to have been
seen before and their orbits can be accurately
measured; possible impacts can thus be predicted
well in advance. Long-period comets have not
been near the Earth during the brief age of
science, so their orbits cannot have been
determined and are therefore impossible to
predict. Such comets may arrive from almost
any direction. These factors make long-period
comets particularly dangerous Ð the more so if
they are dead and therefore difficult to observe.
Even with very large special survey telescopes

we could have less than a year's warning of a
possible impact (see Chapter 8).
A comet can be many times more damaging than
an asteroid of the same mass. This is because comets
on average have an impact speed about twice that of
an asteroid, and their energy or destructive power
goes as the square of their velocity.

Numbers Estimates of the numbers of Near Earth Objects of

different sizes can be made either by direct
measurement using ground-based telescopes or by
observing the numbers and sizes of craters on the
Moon or on the planet Mercury. The graph below

NUMBERS OF NEAR EARTH ASTEROIDS above a given diameter.
The uncertainties in the numbers are indicated. Based with thanks
on an unpublished diagram from Alan Harris of NASA/ JPL
including data from Rabinowitz et al (2000).

1
10

10m 100m 1km 10km
DIAMETER

100
1, 000
10,000
100,000
1, 000,000

NUMBER
Number of near Earth asteroids
of diameter above 100m in
range 30,000 to 300,000

Number above 1km in
range 500 to 1,500

SOURCES OF COMETS: the source of long-period comets
is the Oort Cloud, a spherical shell of billions of comets
around the outer edge of the Solar System; occasionally
a comet is deflected from the cloud to an orbit coming
close to the Sun and Earth (shown). Because the shell is
spherical, the comet can arrive near the Earth from any
direction. Short-period comets come from the
Edgeworth-Kuiper belt beyond the planet Neptune,
much closer to the Sun; these comets generally lie in the
plane of the planets. Diagram not to scale.

COMET HALE-BOPP photographed over Stonehenge
early in 1997.

ORBITS OF HALLEY'S COMET AND HALE-BOPP: the
former, a short period comet, returns every 76 years.
Hale-Bopp is a long-period comet first seen by
telescopes in 1995; the plane of its orbit is at an
angle to the plane containing the planets. Both
comets are unusually large: the former is about 10
kilometres long and the latter 40 kilometres.

David
Asher

Paul
Sutherland,

Galaxy
Picture
Library

100,000 AU
40,000 AU

Edgeworth-Kuiper Belt orbit of Neptune

Oort Cloud
0rbit of a typical
comet

orbit of a typical
comet 14
14Page 1516
14
shows the results of bringing together both these
methods of estimation, for asteroids only. Comets
would increase the numbers by only a few per cent.
There are roughly 1,000 near Earth asteroids of
diameter greater than 1 kilometre, and about
100,000 with diameters greater than 100 metres.

However, the numbers are very uncertain: for
asteroids above 1 kilometre the correct number could
be anywhere in the range 500 to 1,500, while for
100-metre asteroids the range is even wider Ð 30,000
to 300,000.These uncertainties underlie the need for
more and better observations.

Chapter 2 Asteroids, Comets and Near-Earth objects 15
15Page 1617
15
effects Environmental on earth
T he atmosphere protects the surface of the Earth from most Near Earth Objects, which burn up or explode at high altitudes. Whether they impact on the surface depends on a number of factors: their size, their composition, their velocity, and the angle of their approach. Unlike some bodies in the Solar System, the Earth carries relatively few scars from past impacts. In the short term, erosion by wind and weather and, in the long term, tectonic plate movement, remove the

traces. Only recently have we been able to detect
some of the major impact craters, ranging from
Chicxulub in Mexico with a diameter of 180
kilometres (caused by the explosion which marked
the end of the dinosaurs), to Ries in Germany with
a diameter of 25 kilometres; and to assess the
magnitude of the environmental effects which must
have been caused. We also have immediate
experience of minor events. For example the
explosion of an object of around 5 metres diameter
at 20 kilometres altitude over the Yukon on 18
January 2000 caused a loud bang, a flash of light, a
shower of fragments, and an electromagnetic pulse
which caused a temporary loss of power transmission
over the area. Further examples of impacts are given
at Annex B.
The main effects of impacts are blast waves,
tsunamis (or ocean waves), injection of material into
the atmosphere, and electromagnetic changes near
the surface. We now look briefly at each. Depending
on its size, a particular Near Earth Object can have
one or more of these effects. The table overleaf
summarises the range of effects for objects of
different diameter; and the graph on page 17 shows
their average frequency of impact.

Blast waves An asteroid colliding with the Earth is travelling at a
speed between 15 and 30 kilometres per second
when it arrives at the top of the Earth's atmosphere.
A comet is much faster, up to about 75 kilometres
per second. For comparison Concorde travels at
about 0.6 kilometres per second. The asteroid or
comet generates powerful shock waves as it enters
the atmosphere, which lead to enormous heating of
both the Earth's atmosphere and the object, which
might be destroyed or vaporised.
Whether or not an object reaches the surface, its
energy is released in an explosion which causes a
blast wave. This wave represents an abrupt change in
pressure that generates a high speed wind, and it is
this wind and the debris it carries which cause most

ENVIRONMENTAL EFFECTS ON EARTH
Chap t e r 3

IMPACT ON JUPITER OF COMET SHOEMAKER-LEVY 9, on
21 July 1994. Before impact the comet broke into a number
of fragments hitting the planet as shown by the belt of
bright spots near the bottom of the picture. The impacts
created fireballs each as big as the Earth. The very bright
spot at the top right is the Jovian moon Io. Photograph
taken at infrared wavelengths by Infrared Telescope Facility
on Mauna Kea, Hawaii.

NASA 16
16Page 1718
16
Chapter 3 Environmental effects on Earth
NEO Yield Crater Average Consequences
diameter megatonnes diameter interval
(MT*) (km) between
impact
(years)

<10 Upper atmosphere detonation of "stones"
(stony asteroids) and comets; only "irons" (iron
asteroids) <3%, penetrate to surface.

75m 10 to 100 1.5 1,000 Irons make craters (Barringer Crater); Stones
produce air-bursts (Tunguska). Land impacts
could destroy area the size of a city
(Washington, London, Moscow).

160m 100 to 3 4,000 Irons and stones produce ground-bursts; comets
1,000 produce air-bursts. Ocean impacts produce
significant tsunamis. Land impacts destroy area
the size of large urban area (New York, Tokyo).

350m 1,000 6 16,000 Impacts on land produce craters; ocean-wide
to tsunamis are produced by ocean impacts. Land
10,000 impacts destroy area the size of a small state
(Delaware, Estonia).

700m 10,000 12 63,000 Tsunamis reach hemispheric scales, exceed
to damage from land impacts. Land impacts destroy
100,000 area the size of a moderate state (Virginia, Taiwan).

1.7km 100,000 30 250,000 Both land and ocean impacts raise enough dust to
to affect climate, freeze crops. Ocean impacts generate
1 million global scale tsunamis. Global destruction of ozone.
Land impacts destroy area the size of a large state
(California, France, Japan). A 30 kilometre crater
penetrates through all but the deepest ocean depths.

3km 1 million 60 1 million Both land and ocean impacts raise dust, change
to climate. Impact ejecta are global, triggering wide-10
million spread fires. Land impacts destroy area size of a
large nation (Mexico, India).

7km 10 million 125 10 million Prolonged climate effects, global conflagration,
to probable mass extinction. Direct destruction
100 million approaches continental scale (Australia, Europe,
USA).

16km 100 million 250 100 million Large mass extinction (for example K/ T or
to Cretaceous-Tertiary geological boundary).
1 billion

>1 billion Threatens survival of all advanced life forms.

IMPACT EFFECTS BY SIZE of Near Earth Object
* 1 MT = explosive power of 1 megatonne of TNT. The
Hiroshima atomic bomb was about 15 kilotonnes; and
the hydrogen device on the Bikini atoll about 10 MT.

After D Morrison et al, p 71, Hazards (T Gehrels, Ed)
1994, including data from Alan Harris in the graph on
page 17. 17
17Page 1819
17
destruction. The area affected by winds of
much greater than hurricane force can be
calculated for air bursts, and it has been
found that Ð as for nuclear weapon
explosions Ð the area of devastation for a
given energy of explosion varies according
to altitude. The air burst caused by the
impact of an object of around 50 metres
in diameter at Tunguska in Siberia in 1908
flattened some 2,000 square kilometres of
forest. Had it struck an urban area, there
would have been an enormous death toll.
Obviously the size of the area affected by
an air burst depends on the composition
and mass of the asteroid and on its path to
the Earth. The 1.2 kilometre diameter Barringer
crater in Arizona was created by a similar-sized iron
asteroid.
For relatively small surface impact events, blast
wave damage is comparable to that caused by air
bursts. However, as the size of the object and
therefore the energy of the impact increases, the
explosion becomes so vast that some of the
atmosphere above the impact site is blown away from
the Earth. In this way the coupling of the energy

into the blast wave is reduced. As a result blast waves
from large objects, like the one that caused the
Chicxulub event, are not expected to devastate
directly more than a few per cent of the Earth's
surface, but the area of devastation on the ground
would be the size of a large country. The immediate
consequence of the blast wave associated with these
large events is local Ð not global scale Ð damage.
Nonetheless it could cause many deaths and great
material damage. It could also have other
consequences which could enhance the
death toll many times. For these really
large objects, the ejection of material into
the atmosphere described below has a far
greater effect in global terms.

Tsunamis Some two-thirds of the Earth's surface is

covered by the oceans so that the chances
of an impact are greater there than on
land. As in the case of impact on land, a
"crater" is produced in the water but such
craters are unstable and rapidly refill. A
30 kilometre crater penetrates through all
but the deepest ocean depths. These flows
create a series of deep water waves, so-called
tsunamis, which propagate outwards
from the point of impact. Such waves are
also set in motion by earthquakes and
underwater land slips. They can travel far
around the Earth with devastating effects.
For example the 1960 earthquake in

ASTEROID AND COMET IMPACT CRATERS on far side of Moon, taken in 1969 by
NASA's Apollo 11 mission. The large crater (top centre) is about 80 kilometres
across. The Moon has no atmosphere to protect it and is constantly bombarded
by asteroids and comets.

NASA

100 million
10 million

10m 100m 1km 10km
DIAMETER

1 million
100 thousand
10 thousand
millennium
century
decade

Average interval in years
between impacts of near Earth
asteroids of different diameters

AVERAGE INTERVAL IN YEARS BETWEEN IMPACTS on the Earth of near
Earth asteroids of different diameters. The underlying data are as for the
graph on page 13, and have the same wide range of uncertainties.
If comets were included, impacts of a given destructive level would be
more frequent by between 10 and 30 per cent. For a 1 kilometre asteroid
the interval is about 200 thousand years; and for a 100 metre one,
about 3 thousand years. Based on an unpublished diagram from Alan
Harris of NASA/ JPL including data from Rabinowitz et al (2000). 18
18Page 1920
Chile caused a tsunami in Japan, some
17,000 kilometres away, that killed at
least 114 people. The maximum height
above sea level in Hawaii for the same
event was 15 metres, with 61 deaths.
Tsunamis travel as fast as aircraft,
and their destructive effects can be
enormous. The destruction is caused
by the amplification in the height of
the waves as the waves approach the
shoreline. The inflow and outflow of
the water mentioned above causes
huge damage to property as well as
risk to life. The evidence of the effects
of large tsunamis, in terms of relocated
rocks, is found widely, the most
extreme example being in Hawaii where
unconsolidated coral is found at 326 metres above
sea level. Asteroid impacts are capable of producing
tsunamis much larger than that associated with the
1960 earthquake, and may occur anywhere in the
oceans. Tsunami from the Chicxulub impact
deposited material widely and often far inland;
recognition of such deposits in Haiti, Texas and
Florida helped to confirm the nature and location
of the event. The tsunami generated by the Eltanin
impact about 2 million years ago is shown on the two
maps on this page.
Objects that are small, or small fragments of larger
objects that break up in the atmosphere, do not usually
reach the Earth's surface. But for objects in the range

of between 200 to 1,000 metres, tsunamis may be the
most devastating of all the consequences of an impact,
because so much of the Earth's population lives near
coasts. Some studies have indicated that an impact
anywhere in the Atlantic of an object 400 metres in
diameter would seriously affect coasts on both sides of
the ocean by tsunamis as much as 10 metres or more
in height at the shore line.

Injection of material into
the atmosphere The clay layer marking the huge Chicxulub event

contains large numbers of particles which were
melted at the time. They are the size of small

ELTANIN IMPACT of a large asteroid into the
south east corner of the Pacific about 2.15
million years ago. The evidence of the impact
comes from the ocean floor which shows
damage over hundreds of square kilometres.
The two maps shown are based on
calculations. The map above shows the wave
front after 5 hours; it is about 70 metres high
and has travelled over 2,000 kilometres. Inset
on the map is a cross section of the crater
formed at impact: it is 60 kilometres wide and
5 kilometres deep. The map to the left shows
that the resulting tsunami would have spread
over the whole Pacific Ocean, reaching Japan
in about 20 hours, and into the Atlantic
affecting the coast of southern Africa.

Steven Ward/ Eric Asphaug, UCal, Santa Cruz

Steven
Ward/ Eric

Asphaug,
UCal,
Santa
Cruz

Chapter 3 Environmental effects on Earth

18 19
19Page 2021
raindrops. Such drops remain in the atmosphere only
for a day or two, and are not therefore important for
reducing sunlight. But the energy they radiate as they
cool would be capable of igniting fires from any
combustible material. Such fires would generate soot
and poison the air with pyrotoxins.
Smaller particles would stay aloft longer, possibly
for months -or, for very big impacts, years -and the
large number of such particles could cause reduction
of sunlight. But if large quantities of water from the
oceans were also injected into the atmosphere, then
the formation of ice crystals on the particles could
help to sweep the dust from the skies. A cooling
effect at the surface of the Earth -the so called
nuclear winter effect -would be caused in the event
of a large number of such particles, and that would
correspond to a very large explosion, say of an object
around 1 kilometre in diameter. The effects on the
Earth of such a winter could be devastating for all
forms of life, including humans. Other chemical
changes would also follow impacts. Temperatures
behind shock waves are such that nitrogen burns in
the oxygen to create nitrogen oxides of various
kinds. These oxides are a source of acid rain, and also

remove ozone from the atmosphere. The effective
screen to solar ultra-violet radiation would therefore
be weakened. It would take time for the ozone layer
to recover.

Electromagnetic effects in
the upper atmosphere Disturbances in the ionosphere from the

atmospheric detonation of a nuclear weapon have
been detected at distances as large as 3,000
kilometres from the explosion. Although this
explosion was at a low altitude, shock waves
occurred at altitudes as great as between 100 and
200 kilometres. Because impacts of Near Earth
Objects are of much higher energy than explosions
of nuclear weapons, the electromagnetic effects will
be correspondingly greater, leading to large scale
heating and high intensity electromagnetic
disturbances. Even from the frequent air bursts that
occur from the impacts of small objects (around 10
times per year), modest disturbances in radio
communications are frequently noted and power
line failures occur. More severe electromagnetic
effects may disrupt other electrical installations.

CLEARWATER LAKES, Quebec, Canada: the beds of the twin lakes Ð of diameters 22 and 32 kilometres Ð were
formed simultaneously by the impact of a pair of asteroids about 290 million years ago. The larger of the two
shows a prominent ring of islands formed from the central uplifted area and covered with impact melts.

NASA

19 20
20Page 2122
20
risk Overall
O ur understanding of the risk to the Earth of impacts from Near Earth Objects depends in part on which of two situations obtains. For objects whose orbits we know accurately in advance, we can predict with some accuracy (for many years to come) the time and place of any potential impact on the Earth. For these objects, the future is thus largely determined, with little statistical uncertainty. However, for objects yet to be discovered (for which the orbits are by definition unknown) we must rely on a statistical
approach. Here, all we can do is to estimate the average
frequency of impact for objects of different size, as
described in Chapter 2; for none of these can the
precise time or place of impact be anticipated.
Clearly, the objective should be to move as many
potentially hazardous Near Earth Objects as possible
from the second category to the first: to move from a
situation of statistical chance to one of certainty, in

which we should be able to plan ahead. Our
recommendations for an advanced observational
programme, to which we give the highest scientific
priority, are framed accordingly.
The present position is as follows. From
measurements over recent years, made largely by
groups in the United States, we know the orbits of
over 400 Near Earth Objects of diameter above 1
kilometre. These measurements allow us to state with
some confidence that none of these is likely to hit the
Earth over the next 50 years (see Annex B-3).
However, it is estimated that a similar number of
objects of this size have yet to be discovered. For
smaller objects -which can also cause great
destruction locally or regionally -we know even less.
For example, we have discovered fewer than 10 per
cent of objects of diameter 300 metres, and a much
smaller proportion of 100 metre objects. Specifically,
we believe that the aim should be to measure over the

OVERALL RISK
Chap t e r 4

Type of event Diameter Average Typical
of impactor fatalities per impact interval (years)

High atmospheric break-up <50m close to zero frequent
Tunguska-like events 50m to 300m 5,000 250
Large sub-global event 300m to 1.5km 500,000 25,000
Low global effect threshold >600m 1.5 billion 70,000
Nominal global effect threshold >1.5km 1.5 billion 500,000
High global effect threshold >5km 1.5 billion 6 million
Rare K/ T scale events (of type associated >10km 6 billion 100 million
with extinction of dinosaurs)

ESTIMATED FATALITIES for a wide variety of different impact scenarios
(after Chapman & Morrison, 1994, Nature 367, 33) 21
21Page 2223
21
coming years the orbits of all objects down to
diameters of 300 metres, by the use of larger telescopes
than those currently employed. These observations
would also improve our statistical knowledge of the
diminishing population of objects as yet undiscovered.
Through this programme, and through studying, as
we recommend, the consequences of impacts and of
the possibilities for mitigation, we should be able to
make more accurate forecasts. This would also
provide a firm foundation on which to increase
general understanding of the problem and to
communicate intelligently with the public in the
event of a real emergency.
The consequences of an impact in terms of
human life are estimated in the table on page 20 for
different kinds of impact, assuming no attempt at
mitigation. The results are inevitably speculative, and
depend on a wide range of factors including the
composition of the object; this range is reflected in
the spread of the numbers. For sub-global events, the
number of fatalities expected in an individual impact
is highly variable. Once the global threshold has been
exceeded, the consequences for each event are
expected to be more uniform. The material damage
produced by an impact and the consequences of that
damage have been less well studied.
Impacts from very large Near Earth Objects with
diameters over 10 kilometres would have global
consequences that could cause the extinction of most
living organisms. Such events are fortunately very
rare. Impacts of objects from a few kilometres in
diameter to 10 kilometres are also rare.
Impacts from objects with diameters of around 1
kilometre can also have global consequences. On
average these are the most dangerous because they
are much more frequent than the objects of the 10
kilometre class and give many more casualties per
impact than the smaller ones. Impacts of smaller
objects, with diameters of a few hundred metres,
would have dramatic local consequences, but are
unlikely to affect the Earth as a whole. For objects
below about 50 metres in size the Earth's atmosphere
usually provides good protection.
Impacts from mid-sized Near Earth Objects are
thus examples of an important class of events of low
probability and high consequence. There are well-

established criteria for assessing whether such risks
are to be considered tolerable, even though they may
be expected to occur only on time-scales of
thousands, tens of thousands or even hundreds of
thousands of years. These criteria have been
developed from experience by organisations like the
British Health and Safety Executive to show when
action should be taken to reduce the risks.
Flood protection, the safety of nuclear power
stations, the storage of dangerous chemicals or of
nuclear waste are all examples of situations in which
rare failures may have major consequences for life or
the environment. Once the risk is assessed, plans can
be made to reduce it from the intolerable to the
lowest reasonably practical levels taking account of
the costs involved.
If a quarter of the world's population were at risk
from the impact of an object of 1 kilometre
diameter, then according to current safety standards
in use in the United Kingdom, the risk of such
casualty levels, even if occurring on average once
every 100,000 years, would significantly exceed a
tolerable level. If such risks were the responsibility
of an operator of an industrial plant or other activity,
then that operator would be required to take steps to
reduce the risk to levels that were deemed tolerable.
For an island country, the risks from tsunami
effects are significant because of the large target area
of the surrounding ocean. The western coast of
Europe, including the United Kingdom, is at risk
from an impact in the Atlantic Ocean or North Sea,
as also are New Zealand or Japan from impacts in
the Pacific Ocean. Destruction to property could of
course be on a massive scale, and might not be
avoidable, and the consequent social and political
consequences could be severe.
The level of the risk to life and property from
Near Earth Objects is largely related to what we
choose to do in the future. If we do nothing, the
consequences would be as described here. But by
discovering and tracking most of the dangerous
objects (at the same time improving our statistical
knowledge of the remainder), and by studying
further the consequences of impacts and the
possibilities for mitigation, we can hope to exert
some control over future events.

NEO Taskforce Report 22
22Page 2324
22
techniques Observational
I n this chapter we outline the astronomical techniques needed to discover most Near Earth Objects above a given size. We then briefly describe the observations necessary to determine the orbit and physical characteristics of any detected object. Most of the measurements can be made with ground-based telescopes and radars, rather than with expensive space-based missions. While some dedicated facilities are essential, much valuable work can be done by occasional or serendipitous use of

telescopes or spacecraft with different prime
scientific aims. In the past amateur astronomers
around the world have contributed to the study of
Near Earth Objects and this should continue. But for
almost all activities dedicated professional work is
essential.

Discovery/ survey Because we cannot predict where new objects may

come from, we must observe the whole sky,
frequently and systematically. This calls for specially
designed wide-angle telescopes with advanced
detector arrays coupled to very fast computers.
They should operate automatically and remotely, and
be dedicated to observations of Near Earth Objects.
An example of such a facility is the US LINEAR
system with two 1m telescopes, observing objects of
diameter above about 1 kilometre. For complete
coverage, survey telescopes are required on good sites
in each hemisphere.
Bigger dedicated telescopes would allow surveys
of smaller objects: a 3 metre instrument would cover
objects down to a few hundred metres in diameter.
In addition, larger ground-based telescopes primarily
intended for extra-galactic surveys, such as the new

British 4 metre VISTA instrument and the 6.5 metre
survey telescope proposed in the United States,
would inevitably detect many Near Earth Objects.
Such large instruments could also help to discover
long-period comets.
Some classes of objects are difficult, or perhaps
impossible, to discover from the ground, for example
asteroids with orbits inside that of the Earth's (Inner
Earth Asteroids). The European Space Agency has
recently studied a space-telescope mission primarily
to survey objects of this type. Missions including
space telescopes, such as the Agency's GAIA proposal
and NASA's SIRTF, could be used to discover such
objects.

Follow-up observations to
determine the orbit of a
Near Earth Object To determine the orbit of an object after its initial

discovery, conventional narrow-angle ground-based
telescopes are needed in each hemisphere. Because a
newly discovered object rapidly becomes fainter as it
moves away from the Earth, follow-up observations
must be made within days of discovery. While some
telescopes should be dedicated to this function,
follow-up observations can be made with pre-arranged
and rapid access to suitable telescopes used
for other purposes. For very accurate and rapid orbit
determinations of a known object which is near the
Earth, radar is an exceptionally useful technique.

The mass and composition
of an asteroid or comet The destructive power of an asteroid depends

primarily on its energy, which is proportional to its

OBSERVATIONAL TECHNIQUES
Chap t e r 5 23
23Page 2425
23
OBSERVATION OF NEAR EARTH OBJECT: an asteroid or comet near the Earth can be discovered because it moves
against the "fixed" background of stars. This is shown in the above three images taken of the same area of the sky at
30-minute intervals. The asteroid, 1997 XF11 is arrowed. It is indistinguishable from the stars except for its
movement.

NEO Taskforce Report
mass. The mass of a Near Earth Object is surprisingly
difficult to measure using ground-based telescopes.
It depends first on knowing the brightness of the
object and the proportion of the Sun's light which it
reflects (called its albedo), from which its size may be
deduced. But we also need to know its density to
determine its mass: the density is deduced from its
chemical composition (icy, carbonaceous, stony or
metallic) using spectroscopic observations at visible
and infra-red wavelengths. Because of the
uncertainties in knowing the albedo (which can vary
by a factor of five or more), the size and therefore the
mass of an observed object can be very greatly in
error. It is also subject to uncertainty in the density.
NASA's recent rendezvous mission, NEAR, has shown
that the asteroid Mathilde has a density substantially
smaller (perhaps by a factor of three) than expected
from its chemical composition; this asteroid must be
porous or consist of a loose aggregation of rocks.
Such uncertainties make it hard to predict
whether a particular asteroid might cause a global or
a regional catastrophe. To do better we can use
ground based radar which Ð as well as measuring the

position and velocity Ð can also determine the size,
shape, gross structure and spin of an object when it is
sufficiently near the Earth, but not its mass. There is
no suitable radar facility in the southern hemisphere.
But for more accurate measurements of mass,
composition and gross structure, space rendezvous
missions are needed. In this way the mass of an
object can be determined by measuring the pull of
its gravitational field on the spacecraft; its shape
measured photographically; and its chemical
composition found using mass spectrometers.
Approximately 20 sub-groups of asteroids and
comets are thought to exist. A rendezvous mission to
a member of each of these would enable direct
information to be determined and linked to
corresponding ground-based spectroscopic
observations of an unvisited object. Relatively
inexpensive microsatellites could fulfil this purpose.
So far, no mission has yet been able to determine
an object's internal composition or whether it is
hollow. Such an observation will be attempted on a
comet by NASA's Deep Impact mission to be
launched in 2004.

James
V
Scotti

©
Arizona

Board
of
Regents 24
24Page 2526
24
and future plans
Current activities

T his chapter describes current work on Near Earth Objects around the world and the organisations involved, government and otherwise (except in the United Kingdom, covered in Chapter 7). United States The United States is doing far more about Near Earth Objects than the rest of the world put together. An essential element is the support of the US Congress. The central programme, to discover 90
per cent of objects above 1 kilometre in diameter in
10 years, is progressing well. The Minor Planet
Center is at the hub of observations worldwide.
In addition, military surveillance facilities in space
and on the ground look continuously for objects and
explosions in the upper atmosphere, including those
from Near Earth Objects. The United States
recognises that observations of Near Earth Objects
bring good science as well as relating to a practical
problem.
The United States National Aeronautics and Space
Administration (NASA) has a ground-based survey
programme with running costs of about $3 million a
year (see Annex C). It is currently centred on two
sites with dedicated robotic United States Air Force
telescopes and advanced solid state detectors (CCDs)
and computers. In New Mexico there are two
1 metre telescopes for the Lincoln Near-Earth
Asteroid Research (LINEAR) team under the
control of the Massachusetts Institute of Technology
(MIT); since 1998 this group has discovered more
large Near Earth Objects than any other group. On
the island of Maui in Hawaii, an advanced 1.2 metre
telescope has been in operation from NASA's Jet
Propulsion Laboratory at Pasadena under the Near

Earth Asteroid Tracking programme (NEAT). The
same group is fitting new CCD detectors to the
classic 1.2 metre Schmidt telescope at Mt Palomar
(California).
The Spacewatch team at the University of Arizona
has a different approach: it uses a 90 centimetre
telescope, but looks for smaller objects over a limited
area of sky. A 1.8 metre telescope is being completed
to extend this work. Near Earth Objects are also
observed at the Lowell Observatory and through the
Catalina Sky Survey, both based in Arizona. Work to
characterise their properties has been carried out by
a number of groups using optical telescopes,
including one operated by MIT. Particularly
important for characterisation and imaging is the use
of powerful radar using the giant radio telescope
controlled by Cornell University at Arecibo, Puerto
Rico, with another at Goldstone in California
controlled by the Jet Propulsion Laboratory.
NASA's space programme on smaller Solar System
objects, costing about $100 million a year, comprises
a number of rendezvous missions to asteroids and
comets (listed at Annex D). The objectives are partly
pure science, but the missions contribute much to
the understanding of Near Earth Objects, which
would be important if countermeasures were
contemplated. The Agency supports most academic
planetary science in the United States. At present the
NEAR mission is in orbit above the surface of the
asteroid Eros, photographing its surface. In 2005 the
Deep Impact mission will project a half-tonne block
of copper on to Comet Tempel 1. Much should be
learnt about the internal structure of the comet by
observing the resulting crater and the material
ejected from it. NASA's space telescopes, present and
future (also at Annex D), while usually directed to

CURRENT ACTIVITIES AND FUTURE PLANS
Chap t e r 6 25
25Page 2627
25
NEO Taskforce Report
other objectives, are also able to observe Near Earth
Objects. These include the Hubble Space Telescope,
the Next Generation Space Telescope and the Space
Infra-Red Telescope Facility (SIRTF). In addition
ground-and space-based surveillance observations by
the US Air Force regularly pick up explosions from
small asteroids in the upper atmosphere.
During the visit of the Task Force to the United
States in March, NASA emphasised the need for
work by other countries to complement their
activities, mentioning three particular points; follow-up
observations of objects which are often
discovered but then lost; the search for smaller Near
Earth Objects; and, in the southern hemisphere, the
lack of dedicated optical telescopes and planetary
radar. NASA emphasised the value of plates taken
over many years by the United Kingdom Schmidt
Telescope in Australia. For the future, the US
National Science Foundation told us of the proposal
for a 6.5 metre wide-angle survey telescope, which
would be of outstanding value for surveying small
Near Earth Objects, although its prime purpose
would be extra-galactic work.

Organisation of
United States activities The US Congress has named NASA to be

responsible in the United States for Near Earth
Objects, assisted by the United States Air Force.
Within NASA, the Headquarters is responsible for
soliciting and selecting all science investigations,
ground-based and space-based, for the detection
and scientific exploration of Near Earth Objects;
for guidance on strategic planning and mission
selection; and for coordination with other agencies
and organisations including international ones. In
addition, a specially created Program Office has
been set up at NASA's Jet Propulsion Laboratory
to co-ordinate ground-based observations to
complete the survey of objects of 1 kilometre and
upwards; to facilitate communications within the
observing community and between the
community and the public regarding potentially
hazardous objects; to respond to public inquiries;
to maintain a publicly accessible catalogue of Near
Earth Objects; to develop a strategy for their
scientific exploration including in situ investigation

by space missions, and to help Headquarters in its role
regarding other US agencies and foreign activities.
Essential to the coordination and archiving of
observations, and the setting of targets for follow-up,
is the Minor Planet Center based at the Smithsonian
Institute at Harvard. The Minor Planet Center is
broadly under the wing of the International
Astronomical Union and is funded in part by NASA
on an annual basis.
In addition we note that the National Science
Foundation is responsible for funding basic science
including astronomy in universities except for work
in planetary science. Some work on Near Earth
Objects is nonetheless being done on National
Science Foundation funded telescopes. The
Department of Defense does not have planetary
defence as part of its remit. But in its normal defence
role in detecting incoming missiles, it observes many
Near Earth Objects from both its ground-and
space-based platforms.

Europe There is no coordinated approach to Near Earth

Objects in Europe. The Spaceguard Foundation
continues to promote interest and helped organise a
major international conference on the subject in
Turin in 1999.The Foundation is based in Italy, and
is closely linked to the Istituto di Astrofisica Spaziale
in Rome, supported by the Italian Research
Council. The Institute is building a small survey
telescope in Italy, and at Pisa there is a group expert
in planetary dynamics and Near Earth Object orbit
calculations. There are also related activities in
universities and institutes including some in France,
Germany, Sweden, Finland, Greece and former
Soviet Union countries. Interest in the subject is
developing in a number of European institutions,
including the Council of Europe. The European
Union and its Commission have no formal policy on
Near Earth Objects at present.
The European Space Agency has a direct and
developing interest. In 2003 it plans to launch its
Rosetta mission to rendezvous with a comet and fly
past two asteroids, following its successful Giotto
mission to Halley's comet. It is also considering plans
to launch the GAIA space telescope mission in about
10 years' time. 26
26Page 2728
26
Chapter 6 Current activities and future plans
In 1999 the Agency's Long Term Policy
Committee recommended that the Agency should
be involved in studying the threat from Near Earth
Objects and possible countermeasures. In addition
the Agency is developing a statement of its possible
future role in this respect for consideration at a
Ministerial meeting on future strategy in 2001.This
meeting will also involve the European Union.
Recently, the Agency's operations centre in
Germany conducted several studies on Near Earth
Objects with the Spaceguard Foundation of Italy.
The first was for a Spaceguard Central Node, a data-centre
for follow-up observations to complement
the Minor Planet Center. A further study was
completed early this year for a Spaceguard
Integrated System for Potentially Hazardous Object
Survey, including the study of a space telescope for
observing objects in inner Earth orbits, and each
object's composition.

The European Southern Observatory has no
formal involvement in work on Near Earth Objects
at present. It has a number of large telescopes and
advanced detectors on excellent sites in the Southern
hemisphere. The United Kingdom is not at present a
member.
The European Science Foundation, which brings
together the research councils and science academies
of most European countries, has activities relevant to
Near Earth Objects: in particular a programme called
IMPACT on the consequences of the impacts of
objects on the Earth. Also relevant is the European
Space Science Committee, supported by the
Foundation.

Elsewhere Outside the United States and Europe there is some

ground-based work on Near Earth Objects, in
particular in Japan, China, Canada and Australia. In
Japan the Japanese Spaceguard Association
operates the Bisei Center with survey
telescopes of 50 centimetres and of
1 metre (not yet completed) for observing both
Near Earth Objects and also space debris
which might threaten Japanese satellites. The
only current activity in the southern
hemisphere is in Australia where there are plans
for a 0.6 metre telescope for operation early in
2001, with NASA funding and participation by
the Catalina Sky Survey in Arizona. Regarding
space, Japanese missions have observed the
comet Halley; so too have spacecraft from the
former Soviet Union, see Annex D.

1 METRE TELESCOPE OF LINEAR, New Mexico. The telescope,
one of two on the site, is equipped with advanced CCD
detectors and high speed computers. It operates automatically
and sends data to the Lincoln Laboratory at MIT for checking
and transmission to the Minor Planet Center. LINEAR has
discovered more Near Earth Objects of diameter greater than
1 kilometre than any other system so far.

MIT
Lincoln

Laboratory,

Lexington,
Mass 27
27Page 2829
27
in Britain Activities
B ritain has long been among the world leaders in astronomy, and has expertise in the disciplines required in the study of Near Earth Objects and the consequences of impact. British industry also has the skills required to contribute through its expertise in solid state devices, information technology, and in telescope and spacecraft design and construction. Through the work of groups in about a dozen universities and other institutions, Britain has
contributed to the international effort in the study of
Near Earth Objects and the consequences of their
impacts on the Earth. However, there is at present no
continuing British involvement in coordinated
programmes to search for Near Earth Objects and
to determine their orbits.
Current strengths in the British contributions
include the theoretical prediction of the evolution of
orbits under the influence of the gravitational field of
planets and other asteroids, the determination of the
size, mass, spin rate, and structure of asteroids from
observations at optical and infrared wavelengths, and
the use of the national meteorite collection as a data
resource for the classification of asteroids. There is
also very important British work on the impact
record on Earth and the Moon, the modelling of
crater formation by impact, and studies of the
atmospheric effects caused by impacts. British
researchers have a longstanding interest in developing
an historical perspective on the impact record from
both geological and human records.
Most support for work on the subject comes from
the Research Councils and the university system.
None of the Councils has a specific remit for work
on Near Earth Objects, but several are involved in
different degrees and ways Ð the Particle Physics and

Astronomy Research Council (PPARC) for
astronomy and space science; the Natural
Environment Research Council (NERC) for the
physical effects of impacts on the Earth (solid land,
oceans and atmosphere); the Biotechnology and
Biological Sciences Research Council (BBSRC) for
effects on living organisms; and the Economic and
Social Research Council (ESRC) for the economic
and social consequences of an impact. PPARC is
obviously the most directly concerned. It does not
carry out astronomical work itself, but responds to
initiatives from the academic community and funds
work accordingly across the field of astronomy.
There are several important centres of space
research in Britain, with
skills in instrument
construction, mission
planning and data
analysis. Closely allied are
centres of space
engineering, both in
industry, national
institutes and universities,
particularly in the field of
small satellite technology,
and in planetary landing
devices. The Ministry of
Defence and the Atomic
Weapons Establishment
have experience relevant to
work on mitigation
possibilities, but at present
the Ministry of Defence
has no specific remit
regarding Near Earth
Objects.

ACTIVITIES IN BRITAIN
Chap t e r 7

THE 1.2 METRE UNITED
KINGDOM SCHMIDT TELESCOPE
at the Anglo-Australian
Observatory, Siding Spring,
Australia has conducted many all-sky
surveys since the mid-1990s.
The resulting plate archive at
Edinburgh is proving very valuable
in determining asteroid orbits. The
telescope was used specifically for
an asteroid survey between 1990
and 1992 in a programme led by
Dr Duncan Steel.

UK
ATC

Royal

Observatory,

Edinburgh 28
28Page 2930
28
F or the first time in the history of the Earth there are possibilities for mitigating the effects of impacts by Near Earth Objects and even, in the longer term, for deflecting them entirely from collision with the Earth. But all this depends on first improving our ability to detect such objects well in advance and to measure accurately their orbits and physical properties -our key science priorities -and on having in place mechanisms, international, national and local, to take the necessary action.
Once an asteroid or comet on a collision course is
identified and its orbit tracked, its likely point and
time of impact can generally be predicted. Such
accurate prediction is rarely possible for most other
natural hazards, such as earthquakes. If the impact is
on the sea, roughly twice as likely as on land, the
resulting tsunamis could affect vast numbers of
people living near coastlines. Wherever the impact,
people could, in principle, be moved to safety, given
sufficient warning and appropriate logistical support,
although the degree of success would depend
crucially not only on the size of the object but also
on its composition, speed and angle of approach, and
on the size of the population in the affected area.
The great majority of impacts will be of smaller
objects of less than a few hundred metres in
diameter, for which moving people should
significantly reduce loss of life. However, extensive
material damage would nevertheless arise.
After impact from a large object -fortunately very
much less common than the smaller ones just
mentioned -it would be difficult to sustain the
population during the long period which might
follow when the Sun's rays were blocked by dust
injected into the atmosphere at the time of

impact. The only realistic course would be to try to
avert the predicted collision.
A number of possible mechanisms have been
considered for deflecting or breaking up potentially
hazardous Near Earth Objects; most would require
the use of a spacecraft with some means of
transferring energy or momentum to the object, for
example by kinetic energy transfer (by heavy
projectiles carried on the spacecraft or by causing a
collision between asteroids), by chemical or nuclear
explosives, or even by mounting "sails" on the object
to harness the Sun's radiation pressure. Some of these
mechanisms are more realistic than others. Given
warnings of decades or centuries, new technological
developments would almost certainly emerge. The
Task Force believes that studies should now be set in
hand on an international basis to look into the
practical possibilities of deflection.
To try to destroy an asteroid or comet in space by
a single explosive charge on or below its surface
would risk breaking it uncontrollably into a number
of large pieces which could still hit the Earth, doing
even more damage. A more promising method
would be to fly a spacecraft alongside the object,
perhaps for months or years, nudging it in a
controlled way from time to time with explosives or
other means. This relatively gentle approach is
particularly important because many asteroids and
comets are held together only by their own very
weak gravitational fields. The longer the time before
impact, the more effective even a small nudge would
be. This is not science fiction. When NASA launches
its Deep Impact mission to comet Tempel 1 in 2004,
the spacecraft will eventually release a half tonne
lump of copper to cause a huge crater in the comet.
Although this is not the objective, the result will also

Chap t e r 8
possibilities Mitigation MITIGATION POSSIBILITIES 29
29Page 3031
29
be to deflect the comet's orbit. However, the
deflection in this case will be small in comparison to
that required to deal with a real threat.
Long period comets present new dimensions of
difficulty. By definition, such comets have never
been seen before. They come unpredictably at all
angles from the outer reaches of the Solar System,
but can usually only be seen when at a distance of
about 5 AU from Earth. Warning of the approach of
such a body could well be less than a year. Urgent
measures and even more powerful rockets and
explosives would then be essential.
Any proposal to use nuclear explosives to deflect
an asteroid or comet could well prove politically
unacceptable in a world that seeks to reduce or
abandon nuclear weapons, even though such

explosives could probably be designed and controlled
to prevent abuse. Indeed, the use of nuclear
explosives might only be contemplated as a last resort
if a major impact were otherwise inevitable.
In considering the prospects for deflection, it
would be necessary to take into account a range of
international treaties and principles including the
original Outer Space Treaty of 1967.The work of
the United Nations Committee on the Peaceful Uses
of Outer Space is also relevant as is the work of the
Inter-Agency Debris Co-ordination Group,
comprising representatives of space agencies of the
United States, Russia, China, India, Japan, Ukraine
and Europe. Some of this group's responsibilities are
similar to those which would be required for any
impacts by Near Earth Objects.

NASA'S DEEP IMPACT MISSION, which will project a 500 kilogramme solid
impactor into a comet, Temple 1 (artist's impression). A flyby spacecraft will
take images and make measurements. The impactor will also take images of
the comet's surface prior to impact. The mission aims to increase
understanding of the composition and structure of comets.

Ball
Aerospace

&
Technologies

Corp 30
30Page 3132
30
be done?
What is to

I f ever there was an issue affecting the whole world, it is the threat from Near Earth Objects. To understand and try to cope with the threat requires an international response. This response should cover not only understanding the science, so that dangerous Near Earth Objects may be predicted and methods of mitigation assessed; but, equally important, how all aspects of this response should be organised. The organisation must cover the identification and coordination of the science, communication with the
public, and work on measures to react to a possible
impact, or deflect or destroy an incoming object.
At present no international institution exists for the
purpose. Spaceguard is a collective term for a variety
of activities which have grown up in a number of
countries over recent years, and which have done
much to alert public opinion. But none has official
recognition except for the US Spaceguard Survey
(the name given to NASA's survey), and so far there
are no specific coordinating mechanisms in any state
or government, even the United States.
The need for an international approach was at the
heart of our terms of reference and is central to our
proposals for action developed in this chapter. Our
terms of reference also asked us to confirm the
nature of the hazard and potential levels of risk,
which we have done in Chapters 2, 3 and 4; to
identify the current British contribution to
international efforts, covered in Chapter 7; and to
suggest how these issues should be communicated to
the public, which we cover in Recommendations 13
and 14 below and the preceding two paragraphs.

Science needs The more we have studied the subject the more we

can see how very little is currently known about Near
Earth Objects, despite the efforts of United States and
other scientists. We do not know accurately how many
objects of diameter about 1 kilometre there are; and
their energies and compositions are very uncertain. We
know very little indeed about smaller objects. Without
this knowledge we have only the roughest idea of the
magnitude of the risk. The science involved is wide-ranging,
involving astronomy but also geophysics,
oceanography, climatology, biology and the social
sciences.
The Task Force has concluded that the overall
needs, worldwide, are as follows:

° for survey and discovery: at least one dedicated 3 metre-class telescope in the southern hemisphere and one in the northern; the

survey of smaller Near Earth Objects; the use
of data from surveys being made for other
purposes; the use of sky survey archives; and
the use of space telescope missions where
appropriate;

° for accurate orbit determinations: one large telescope in each hemisphere, preferably dedicated; some time by right on various

existing instruments;
° for composition and gross properties: access to large telescopes and space rendezvous missions;

° for academic studies: in particular of Near Earth Objects' interactions with the atmosphere, oceans, solid earth, climate and

living things, including historical evidence; and
the effects on people and society.

What fair contribution should Britain make to
fulfilling these needs? We have taken account of

WHAT IS TO BE DONE?
Chap t e r 9 31
31Page 3233
31
NEO Taskforce Report
existing telescopes or those under construction in
which the United Kingdom is a partner; the skills of
British scientists and engineers, and industry; and our
view that partnership in Europe in this task is
desirable.

Survey and discovery To make a substantial contribution to the need both
for surveys in the southern hemisphere and for
systematically discovering smaller Near Earth
Objects, we propose the construction of an advanced
new 3 metre-class telescope on an excellent site. We
have considered the possibility of using older
existing telescopes for the systematic survey and
discovery of these objects, but have generally rejected
the idea because adapting such equipment would be
expensive and the resulting telescopes would not be
competitive for long. Only a new dedicated
telescope would make a satisfactory contribution to
the world effort. Because such a facility would be
expensive, we believe that this project should be
shared with other countries, preferably in Europe.

Recommendation 1
We recommend that the Government should seek
partners, preferably in Europe, to build in the
southern hemisphere an advanced new 3 metre-class
survey telescope for surveying substantially smaller
objects than those now systematically observed by
other telescopes. The telescope should be dedicated to
work on Near Earth Objects and be located on an
appropriate site.

Much valuable data has been gathered cheaply
from observations made for purposes unrelated to
Near Earth Objects. An excellent example is the
photographic archive, at the Royal Observatory
Edinburgh, of the United Kingdom Schmidt
Telescope in Australia. These records contain
invaluable historical detections of Near Earth
Objects which greatly enhance the use of current
observations. The records are being converted to
digital form and posted on the internet for use by
astronomers worldwide, with funding from the
Particle Physics and Astronomy Research Council.
We hope that this will continue. Plates taken with
United States Schmidt telescopes are also being
digitised, widening this important database.

Furthermore, we wish to encourage Near Earth
Object discovery by efficient use of suitable current
and future wide-angle survey telescopes dedicated to
other aims.

Recommendation 2
We recommend that arrangements be made for
observational data obtained for other purposes by
wide-field facilities, such as the new British VISTA
telescope, to be searched for Near Earth Objects on a
nightly basis.

No current space telescope is dedicated to the
discovery of Near Earth Objects. However, a number
of existing and planned missions are, and will be, able
to detect objects incidentally when making
observations for quite different purposes. We strongly
suggest that consideration be given by space agencies
to consider the use of space missions for incidental
observations of Near Earth Objects. Apart from
existing telescopes (see Annex D), the European
Space Agency's proposed GAIA mission and NASA's
SIRTF project could each be used in this way
without substantially modifying the mission or
curtailing its main purpose.

Recommendation 3
We recommend that the Government draw the
attention of the European Space Agency to the
particular role that GAIA, one of its future missions,
could play in surveying the sky for Near Earth
Objects. The potential in GAIA, and in other space
missions such as NASA's SIRTF and the European
Space Agency's BepiColombo, for Near Earth Object
research should be considered as a factor in defining
the missions and in scheduling their completion.

Accurate orbit
determination A particularly urgent requirement is for observations

to determine the orbits of Near Earth Objects
discovered by United States telescopes but
subsequently lost. This needs one or more
professionally run telescopes. The l metre Johannes
Kapteyn Telescope on La Palma in the Canary
Islands, owned by the United Kingdom and
international partners, could immediately fulfil this
need, economically and without modification. This
would not only fulfil an urgent need, but would also 32
32Page 3334
32
Chapter 9 What is to be done?
enable Britain to contribute immediately to the
international programme of observations.

Recommendation 4
We recommend that the 1 metre Johannes Kapteyn
Telescope on La Palma, in which the United Kingdom
is a partner, be dedicated to follow-up observations
of Near Earth Objects.

Composition and gross
properties The importance of determining the composition

and gross physical characteristics of a Near Earth
Object both to predict the way it would impact on
the Earth and in planning mitigation possibilities
including deflection, were emphasised in Chapters 2,
5 and 8.
On the ground-based side, the scientific
requirements could be fulfilled immediately by a
number of existing telescopes to which the United
Kingdom has access. For the southern hemisphere
there is the 3.9 metre Anglo-Australian Telescope; in
the north there are the 4.2 metre William Herschel
and the 2.5 metre Isaac Newton Telescopes on La
Palma in the Canary Islands, and in Hawaii the 3.8
metre United Kingdom Infra-Red Telescope. All are
heavily over-subscribed; hence we believe that an
arrangement should be made for small amounts of
time to be provided under appropriate financial
terms for spectroscopic follow-up. Several of the
European Southern Observatory's telescopes in
Chile would also be excellent for this work. We have
considered the great value of radar observations for
determining an object's gross structure and accurate
orbit and noted that no such facility exists in the
southern hemisphere. However, we do not propose
any major British involvement in radar at this stage.

Recommendation 5
We recommend that negotiations take place with the
partners with whom the United Kingdom shares
suitable telescopes to establish an arrangement for
small amounts of time to be provided under
appropriate financial terms for spectroscopic follow-up
of Near Earth Objects.

Space rendezvous missions to asteroids or comets
give a unique insight into the characteristics of the
asteroid or comet being visited (Annex D).

A systematic assessment of different types needs
many missions, perhaps 20, to enable each type
subsequently to be recognised by ground-based
techniques, of great importance should
countermeasures be needed. For this limited purpose
it might be possible to use a series of essentially
identical micro satellites, each launched economically
piggy-back with other spacecraft; in this way the
unit cost should be much below that of current
rendezvous missions. We note that the United
Kingdom is a leader in micro satellite technology.
We suggest that a beginning could be made with
a single demonstration mission.

Recommendation 6
We recommend that the Government explore, with
like-minded countries, the case for mounting a
number of coordinated space rendezvous missions
based on relatively inexpensive microsatellites, each to
visit a different type of Near Earth Object to establish
its detailed characteristics.

Coordination of
astronomical observations The systematic archiving of the data and rapid

dissemination of recommendations for follow-up by
other observatories is essential. This role is carried
out by the Minor Planet Center in Boston; the
Spaceguard Central Node in Europe is designed to
have a complementary role. We suggest that the
United Kingdom and other governments, together
with the International Astronomical Union, NASA
and other interested parties, seek ways of putting the
governance and funding of the Minor Planet Center
on a robust international footing, including the
Center's links to executive agencies should a
potential threat be found. The role of the Spaceguard
Central Node should also be considered.

Recommendation 7
We recommend that the Government Ð together with
other governments, the International Astronomical
Union and other interested parties Ð seek ways of
putting the governance and funding of the Minor
Planet Center on a robust international footing.
including the Center's links to executive agencies if
a potential threat were found. 33
33Page 3435
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NEO Taskforce Report
Studies of impacts and
environmental and social
effects The prediction of the consequences of an impact

requires, in addition to work by astronomers,
interdisciplinary research by geophysicists,
oceanographers, climatologists, social scientists and
others. In the United Kingdom such activities are
supported by the universities and by the Research
Councils (including Natural Environment Research
Council, and the Economic and Social Research
Council). The European Science Foundation is
currently supporting a limited programme in this
area. Such research is not only of great practical
importance, but also excellent science. The British
Government should encourage high quality research
in these areas.

Recommendation 8
We recommend that the Government should help
promote multi-disciplinary studies of the
consequences of impacts from Near Earth Objects on
the Earth in British and European institutions
concerned, including the Research Councils,
universities and the European Science Foundation.

Mitigation possibilities The consequences of the impacts of most Near
Earth Objects can probably be mitigated, or the
objects themselves deflected, if we have determined
their orbits in good time (Chapter 8). However, the
arrangements needed are not simple and should be
planned well before the prospect of any impact. The
Government should consider participating soon with
others in studies on mitigation possibilities, including
of deflection methods for example through the
European Space Agency or with the United States.

Recommendation 9
We recommend that the Government, with other
governments, set in hand studies to look into the
practical possibilities of mitigating the results of
impact and deflecting incoming objects.

Organisational needs The Task Force has considered what kind of
structure would best meet the organisational
requirement. There is an obvious need for some
international forum for discussion of the scientific
aspects of the problem. There is an equally obvious
need for a forum for intergovernmental action.
Without a strong connection between the two, not
least to cope with rising public interest in the
subject, proper coordination could not be achieved.
There are no obvious precedents, although the
emerging international arrangements to manage the
problems of climate change come closest. A crucial
difference is that while climate change is long term
with accumulating effects, threats from Near Earth
Objects could come tomorrow, in 50 years or in a
thousand. Nonetheless the results of current research
and greater understanding of the problem will
maintain the current momentum of interest, which
would of course accelerate in the event of a possible
catastrophe. Any institutions, international or
national, would then be put to immediate test.
There is a hierarchy of possibilities which we now
examine: first is the international structure; next
European arrangements; then a British national
structure; finally division of responsibilities within
the national structure.
No United Nations body or agency, can at present
be held to represent the global interest in protection
from Near Earth Objects. The UN Committee on
the Peaceful Uses of Outer Space is too narrowly
focused, and UNESCO with its brief on science in
general is too wide. Although the Task Force is
reluctant to suggest new institutions, something on
the lines of the Intergovernmental Panel on Climate
Change seems most nearly to meet the requirement.
This Intergovernmental Panel has three main
working groups: one on science; one on the impacts
of change; and one on how change might be
mitigated. The Panel, which brings together experts
from all over the world, produces Assessments every
few years, and has been an outstanding success. An
Intergovernmental Panel on Threats from Space,
financed by participating governments, would
provide a light and unbureaucratic mechanism for
coordination and consultation, issuing periodical 34
34Page 3536
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Chapter 9 What is to be done?
Assessments as the situation required. Whether more
formal arrangements were desirable, on the analogy
of the Framework Convention on Climate Change
with its successive meetings of the Parties, could be
determined in the light of events.

Recommendation 10
We recommend that the Government urgently seek
with other governments and international bodies (in
particular the International Astronomical Union) to
establish a forum for open discussion of the scientific
aspects of Near Earth Objects, and a forum for
international action. Preferably these should be
brought together in an international body. It might
have some analogy with the Intergovernmental Panel
on Climate Change, thereby covering science,
impacts, and mitigation.

We recognise that interim measures may be
needed before the integrated international structure
we prefer could be fully established. In this, the
International Astronomical Union, which is already
doing much on the science side, should play an
important role. Indeed, we expect that a final
organisation based on the structure of the Inter-Governmental
Panel on Climate Change would
wish to continue to involve the International
Astronomical Union. Regarding inter-governmental
aspects, the Inter-Agency Debris Coordination
group (covering the space agencies of United States,
Russia, China, India, Japan, Ukraine and Europe)
might be able to contribute; and for certain aspects,
the UN Committee on the Peaceful Uses of Outer
Space.
At European level (see Chapter 6), the European
Space Agency among other European institutions
has already taken up the subject and could develop
its interest further on behalf of its member states.
The European Southern Observatory, of which most
European countries are members, though not
Britain, could play a major role in the study of Near
Earth Objects with its facilities on excellent sites in
the Southern hemisphere. The European Science
Foundation, which brings together the research
councils and science academies of most European
countries, could help to provide and coordinate
across Europe a broad base for research on all aspects
of the impact problem, physical, biological and
social. It already has a programme in the area and

funds the European Space Science Committee with
strong links to scientists in the United States.
Because the threat covers all aspects of life, we
believe that the European Union should also be fully
engaged.
We believe that the Government should discuss
with other governments how Europe could best co-ordinate
actions regarding Near Earth Objects, and
how best to work closely with the United States,
with complementary roles in specific areas, and with
other interested countries. As a first step we suggest
that the European Space Agency and the European
Southern Observatory, with the European Union
and the European Science Foundation, be asked to
propose a strategy for this purpose. It could be
discussed at the ministerial meeting of the European
Space Agency in 2001.

Recommendation 11
We recommend that the Government discuss with
like-minded European governments how Europe could
best contribute to international efforts to cope with
Near Earth Objects, coordinate activities in Europe,
and work towards becoming a partner with the
United States, with complementary roles in specific
areas. We recommend that the European Space
Agency and the European Southern Observatory, with
the European Union and the European Science
Foundation, work out a strategy for this purpose in
time for discussion at the ministerial meeting of the
European Space Agency in 2001.

At national level no central coordinating body for
Near Earth Objects has yet been formally identified
within the government. In the event of any
emergency, possible or real, virtually all parts of
government would be involved, and the Cabinet
itself would have to determine policy. This suggests
that some Cabinet committee or ad hoc group,
bringing in the Department of Trade and Industry,
the Home Office, the Ministry of Defence, the
Department for the Environment, Transport and the
Regions, the Ministry of Agriculture, the Foreign
and Commonwealth Office and other interested
departments should be envisaged.
The interim responsibility rests with the Minister
for Science within the Department of Trade and
Industry, covering the British National Space Centre
and the Office of Science and Technology. The Task 35
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NEO Taskforce Report
Force believes that a lead department should be
formally designated, and lines of responsibility
established against all eventualities.

Recommendation 12
We recommend that the Government appoint a single
department to take the lead for coordination and
conduct of policy on Near Earth Objects, supported
by the necessary inter-departmental machinery.

The lead department in Whitehall should act as
the channel for recommendations to the
Government, The Task Force would not expect this
department to undertake all coordination and
management itself. Instead the Task Force believes
that a British Centre for Near Earth Objects should
be set up whose mission would be to promote and
co-ordinate work on the subject in Britain; to
provide an advisory service to the Government,
other relevant authorities, the public and the media;
and to facilitate British involvement in international
activities, whether through the means suggested
above or through the International Astronomical
Union and such other bodies as the Minor Planet
Center in Boston. In doing so it would call on the
Research Councils involved, in particular the
Particle Physics and Astronomy Research Council
and the Natural Environment Research Council, and
on universities, observatories and other bodies
concerned.
The role of such a Centre would obviously evolve
with experience. The closest analogy would be with
the recently created Climate Change Centre to
be established at the University of East Anglia.
It should, like this, be unbureaucratic, and become
the centre of a network in Britain but reaching
elsewhere, with special responsibility for relations
with the public. In this respect its objective would be
to communicate in clear, direct and comprehensible
language, avoiding excessive alarm or excessive
complacency, with some very different audiences: on
one hand Parliament, the general public and the
media, and on the other the scientific, academic and
environmental communities. The Task Force suggests
that as a first step there should be a feasibility study
to determine the terms of reference for such a
Centre and how it might be financed.

Recommendation 13
We recommend that a British Centre for Near Earth
Objects be set up whose mission would be to promote
and coordinate work on the subject in Britain; to
provide an advisory service to the Government, other
relevant authorities, the public and the media, and to
facilitate British involvement in international
activities. In doing so it would call on the Research
Councils involved, in particular the Particle Physics
and Astronomy Research Council and the Natural
Environment Research Council, and on universities,
observatories and other bodies concerned in Britain.

Recommendation 14
We recommend that one of the most important
functions of a British Centre for Near Earth Objects be
to provide, a public service which would give
balanced information in clear, direct and
comprehensible language as need might arise. Such a
service must respond to very different audiences: on
the one hand Parliament, the general public and the
media; and on the other the academic, scientific and
environmental communities. In all of this, full use
should be made of the Internet. As a first step, the
Task Force recommends that a feasibility study be
established to determine the functions, terms of
reference and funding for such a Centre.

In suggesting arrangements of this kind Ð
international, European and national Ð the Task
Force has not attempted more than a sketch of the
possibilities. The threat from Near Earth Objects
may be a very old problem, going back to the
origins of life, but recognition of the threat is new in
human experience. Greater understanding of the
problem is now coupled with the possibilities of
mitigation. The creation of the structure proposed
above would form a base for action, if it ever
became necessary, and in the meantime give some
measure of reassurance. There is no question more
often asked of the Task Force: What is the point of
worrying about the threat when we can do nothing
about it? The answer is that we need to know far
more about it than we do, and that with such
knowledge something might indeed be done about
it. 36
36Page 3738
36
Chronology 4.5 billion years ago the Earth was formed from material like that of asteroids and comets; and has
been bombarded by Near Earth Objects (NEOs)
ever since. Annex B gives specific examples of past

impacts on the Earth and some recent near misses.
This annex summarises the history of human
understanding of asteroids and comets over the last
three centuries.

CHRONOLOGY

Annex A

Year Event
1694 Edmond Halley suggests that cometary impacts may have caused global catastrophes, formed the
Caspian Sea as an impact crater, and might be linked to the biblical flood legend. This idea revived from
time to time (for example by William Whiston)

1790s Pierre Simon de Laplace suggests comet impacts cause terrestrial catastrophes
1794 Chladni proposes that meteorites are of extra-terrestrial origin
1801 First asteroid discovered (Ceres); discovery of more Main Belt asteroids soon follows
1822 Lord Byron suggests that mankind could save itself from comet collisions by diverting them
1890s Alexander Bickerton suggests that impacts have sculpted the face of the Earth. Barringer suggests the
"Meteor" Crater in Arizona is of impact origin

1898 Eros, first Earth-approacher discovered (Amor-type asteroid)
1930s Odessa crater in Texas shown to be an impact crater: the first proven case on Earth
1932 First two Earth-crossing asteroids discovered, Apollo and Adonis
1937 Asteroid Hermes (1937 UB), size about 800 metres, observed for few days only as it misses Earth by just
670,000 kilometres (60 per cent further than Moon). Insufficient data to secure orbit, so Hermes is lost; it
may come back close to Earth at any time

1941 Fletcher Watson estimates rate of impacts on Earth
1947 Minor Planet Center established by the International Astronomical Union (IAU) in Cincinnati, Ohio;
moves to Cambridge Massachusetts, 1978

1948Ð 51 Edgeworth (1948) and Kuiper (1951) predicted belt of comets, just beyond Neptune, much nearer Sun
than Oort cloud. Now known as EdgeworthÐ Kuiper Belt

1949 Ralph Baldwin explains lunar craters as being of impact origin
1949 Icarus, a close Earth-approacher discovered (Apollo-type asteroid)
1950 Oort cloud hypothesis; billions of comets in spherical shell around solar system, 50,000 AU from Sun
1951 Ernst Öpik (Armagh), after earlier work, estimates cratering rates on Earth
1954 First Aten-type "Inner-Earth" asteroid discovered (1954XA) but subsequently lost
c. 1960 Eugene Shoemaker proves impact origin of Barringer (Meteor) Crater (Arizona)
1970 Eleanor Helin (JPL) and Eugene and Carolyn Shoemaker start systematic photographic survey of NEOs
1973 Arthur C Clarke coins term Spaceguard in his novel "Rendezvous with Rama"
1979 Film Meteor released
before Nuclear winter calculations in context of full nuclear war: subsequently realised to be applicable to
1980 consequences of an NEO impact

1980 Alvarez et al propose that a massive asteroid impact led to the extinction of the dinosaurs. Later linked
to event at Chicxulub

1981 NASA conference: Collision of Asteroids and Comets with Earth: Physical and Human consequences
July

1981 "Spacewatch": Tom Gehrels and Bob McMillan, University of Arizona, began programme to survey NEOs
including small asteroids, with electronic detection and data collection. Survey began late 1988 37
37Page 3839
37
Year Event
1990 Duncan Steel's survey of asteroids begins using United Kingdom Schmidt Telescope in Australia
1990 American Institute of Aeronautics and Astronautics makes recommendations concerning NEOs to
US Congress

1990 US Congress House committee in NASA Multiyear Authorisation Act of 1990: "imperative that detection
Sept rate of Earth-orbit-crossing asteroids must be increased substantially, and that means to destroy or alter
the orbits... should be defined and agreed internationally"

1991 US Congress House Committee on Science and Technology use NASA Authorisation Bill to direct NASA to
study 1) a programme to increase detection rate of Earth-orbit-crossing asteroids, addressing costs,
schedule, technology, and equipment (Spaceguard Survey Report); 2) systems and technologies to
destroy or alter orbits of such asteroids if they should pose a danger to life on Earth (NEO Interception
Workshop)

1992 Spaceguard Survey Report delivered to US Congress. Recommends a search programme and
Jan international collaboration to find greater than 1 kilometre objects; and the provision of six ground
based telescopes, northern and southern hemisphere sites, southern hemisphere radar; half costs to
come from international partners

1992 NEO Interception Workshop. Full investigation of counter-measures concluded that nuclear explosives in
Jan stand-off mode most likely to succeed (see 1991 above)

1992 Three witnesses testify before US Congress on results of above workshops
March

1993 European Science Foundation initiates new scientific network "Impact Cratering and Evolution of Planet
Earth"

1994 US Congress House Committee on Science and Technology pass an amendment to NASA Authorisation
Feb Bill directing NASA to report within a year with a programme to identify and catalogue, with help from
the Department of Defense and space agencies of other countries, within 10 years, orbital characteristics
of all comets and asteroids greater than 1 kilometre diameter and in an orbit that crosses Earth's

1994 Shoemaker-Levy 9 comet collides with Jupiter. At least 21 cometary fragments, with diameters up to
July 2 kilometres, cause massive explosions and spark public interest

1994 IAU's 22nd Assembly's Working Group on NEOs, present a report recommending that an international
authority should take responsibility for NEO investigations
1995 Near Earth Objects Survey Workgroup Report is released with a programme to meet Congress'
June requirements. Recommends NASA, USAF and international collaboration; two dedicated 2 metre
discovery telescopes; use of two existing 1 metre telescopes for survey and follow-up; enhanced funding
to obtain roughly half time on a 3 to 4 metre telescopes for physical observation; MPC enhancements

1995 UN host conference on NEOs attended by representatives of UN Office of Outer Space Affairs
1995 IAU's Working Group on NEOs workshop sets up the Spaceguard Foundation to promote
international NEO discovery, follow-up and study
1996 UN meeting in Colombo, Sri Lanka, resolves that an international network of telescopes under UN aegis
Jan is needed for NEO searching and tracking

1996 Parliamentary Assembly of the Council of Europe, Resolution 1080, detection of asteroids and comets
that are potentially dangerous to mankind

1997 Spaceguard UK set up to promote British NEO activities
1998 Two new major NEO search programmes start in United States using Department of Defense facilities:
NEAT in Hawaii and LINEAR in New Mexico Ð see Annex C Ð leading to step-increase in NEO discovery rate

1998 National Research Council of US National Academy of Sciences: highest priorities to NEOs
1998 US Congressional Hearings on NEOs and Planetary Defense. Recommends use of more GEODSS
May telescopes, states difficulties with using already existing observatories

1998 NASA NEO Program Office set up at JPL to help coordinate and provide a focal point for US studies of
NEOs

1998 Armageddon and Deep Impact films released, both about NEO collisions with the Earth
Jul-Aug

1999 In a report to the ESA Council at Ministerial level, ESA's Long Term Policy Committee recommend that
the Agency be involved in NEO activities, including the study of countermeasures

NEO Taskforce Report 38
38Page 3940
38
Year Event
1999 Threat from NEOs is debated in House of Commons. Minister for Energy and Industry, John Battle, says
March that Government will consult British astronomers and other experts on ways the UK can support NEO
research

1999 Threat from NEOs discussed in House of Lords. Science Minister, Lord Sainsbury, says that Britain must
June co-operate internationally on this topic

1999 International Monitoring Programs for Asteroid and Comet Threat (IMPACT) conference in Italy
June organised by the IAU, the Spaceguard Foundation and others. Outcomes include the "Torino Scale" to
describe risk and severity of possible impact for newly discovered objects

1999 UNISPACE III, a UN Space conference, hold a workshop on NEOs and make recommendations to UN
July General Assembly. Subsequently, resolution adopted by conference, the Vienna Declaration on Space
and Human Development, declares a strategy including actions that should be taken to improve
knowledge of NEOs; improve international coordination of activities relating to NEOs; harmonise
worldwide effort to identify, follow up and predict NEO orbits; and research safety measures on the use
of nuclear power sources in outer space

2000 UK Government sets up a Task Force on Potentially Hazardous NEOs
Jan

Annex A Chronology

More information can be found in the Bibliography 39
39Page 4041
39
of asteroids and comets
Impacts and close approaches IMPACTS AND CLOSE APPROACHES

OF ASTEROIDS AND COMETS

Annex B

Section B-1: Some major impacts of asteroids and comets;
Section B-2: Documented impacts in last decade;
Section B-3: Close approaches.

B-1: Some major impacts of asteroids and comets
Age (years) Place Notes
or date references in square brackets below given in Bibliography

2,000 million South Africa Vredefort, oldest known crater on Earth, estimates of
crater diameter vary from 140 kilometres to
300 kilometres [1]
290 million Canada Clearwater Lakes, two craters of diameters
32 kilometres and 22 kilometres [2]
250 million Australia Woodleigh, 130 kilometre crater, discovered April 2000.
Explosion thought to be source of the massive Permian-Triassic
extinction of almost all life on Earth [3]
215 million Quebec, Canada Manicouagan, 150 kilometre crater [4]
200 million Chad, Africa Aorounga, chain of several large craters from multiple
impact, each >10 kilometres [5]
143 million Australia Gosses Bluff, 22 kilometre crater [6]
100 million Canada Deep Bay, 13 kilometre crater [7]
65 million Yucatan peninsula Chicxulub, 170 kilometre scar, mass extinction
(dinosaurs) [8]
38 million Canada Mistastin Lake, 28 kilometre crater [9]
35 million USA Chesapeake Bay 85 kilometre crater [10]
5 million Namibia, Africa Roter Kamm, ~3 kilometre crater [11]
3 million Tajikistan Kara-Kul, ~50 kilometre crater [12]
2.15 million SE Pacific Ocean Eltanin asteroid impact causing tsunami,
Asteroid size > 1 kilometre [22]
1 million Ghana, Africa Bosumtwi, 10.5 kilometre crater [13]
300 thousand Australia Wolfe Creek, 0.9 kilometre crater [14]
49 thousand Arizona, USA Barringer or "Meteor" Crater, 1.2 kilometre crater [15]
120 to 600 Saudi Arabia Wabar Craters in Empty Quarter of Saudi Arabia [17]
1490 not confirmed China About 10,000 people reported killed [16]
1908 Siberia, Russia Tunguska, stony object, diameter ~60 metres, exploded
at altitude of ~ 8 kilometres, flattening over 2000 square
kilometres of trees and starting fires. 10Ð 20 MT [18]
1930 Brazil Tunguska-like airburst of 10Ð 50 metre object, significant
ground damage; no crater identified [19]
1947, Feb Russia Sikhote-Alin, one hundred craters, above 0.5 metre
(longest about 14 metres) resulting from an iron object
breaking up at ~ 5 kilometres [20]
1994, Jul Comet Shoemaker-Levy 9 Fragmented comet collided with Jupiter
collision with Jupiter creating Earth-sized impact zones [21] 40
40Page 4142
40
Annex B Impacts and close approaches of Asteroids and Comets
B-2: Documented impacts on Earth in last decade
Date Location Diameter of
object (metres)

1990, Apr 7 Netherlands (house hit)
1990, Jul 2 Zimbabwe
1991, Aug 31 Indiana, USA
1992, Aug14 Uganda (building hit)
1992, Oct 9 Peekskill, New York (car hit)
1994, Nov 1 Pacific Ocean 39
1994, Nov 3 Bay of Bengal 15
1994, Dec 7 Fort McMurray/ Fort Chipewyan, Alberta 3
1994, Dec 16 1000 kilometres south of Cape of Good Hope at 30km altitude 7
1995, Jan 18 Northern Mongolia. 25 kilometres altitude 10
1995, Feb 16 Pacific Ocean 8
1995, Feb 16 Pacific Ocean (10 hours later) 4
1995, Jul 7 Near New York City 12
1995, Dec 9 Cuenca, Ecuador 11
1995, Dec 22 1500 kilometres south of Argentina (Antarctica) >2
1996, Jan 15 2000 kilometres south of New Zealand >3
1996, Mar 26 West of the coast of Mexico 3
1996, Mar 29 Hawaii 10
1996, Mar 30 1000 kilometres west of Chilean coast 11
1997, Apr 27 Indian Ocean, West of Australia 27
1997, Sep 5 South of Mauritius, Indian Ocean 14
1997, Sep 30 Off coast of South Africa 5
1997, Oct 1 Mongolia 8
1997, Oct 9 Near El Paso, Texas. 36 kilometres altitude >12
1997, Dec 9 Near Nuuk, Greenland ?
1998, Jan 11 Near Denver, Colorado >2
1999, Jul 7 North Island, New Zealand. 28.8 kilometres altitude >2
1999, Dec 5 Near Montgomery, Alabama. 23 kilometres altitude >2
2000, Jan 18 Yukon, 25 kilometres altitude 5

The first five impacts above were reported in Lewis J S, Rain of Iron and Ice, Reading, Mass, Addison-Wesley,
1996.The remainder were reported from US Air Force Early Warning Satellites.

Note that between August 1972 and March 2000, sensors in these satellites detected 518 impact
events, all in the kilotonne of TNT class or above (objects above a few metres in diameter); this
averages 30 events per year. Most of these events were primarily bursts in the upper atmosphere
and were not detected at ground level. 41
41Page 4243
2: Objects 200 metres and larger which were discovered after they had passed within
two lunar distances some time in the last century. This conclusion was reached by calculating
the past orbit of each newly discovered object.

1: Objects which were discovered as they approached the Earth to within 2 lunar
distances. These are given chronologically by the date of closest approach. The lunar, or Earth to
Moon, distance is about 400,000 kilometres.

41

NEO Taskforce Report
B-3: Close approaches
This Section analyses Near Earth Objects which have been observed over recent years to have
come closer than two or four lunar distances of the Earth. The first two lists below cover close
approaches in the past; the remaining two are predictions for the future.

Although objects of all sizes are included, those under a few tens of metres in diameter would
burn up in the upper atmosphere. The conclusion is that no known object presents a serious
hazard over at least the coming 50 years. However, only about half the 1 kilometre objects have
yet been discovered and a much smaller proportion of small ones. The Section is based on
information kindly supplied by Brian Marsden and Gareth Williams of the Minor Planet Center,
Boston (and some data from Andrea Milani's "riskpage" website, see Bibliography).

Minimum approach Date of closest approach Object approx diameter
(in lunar distances) (metres)

1.96 1937 Oct 30 1937 UB (Hermes) 1,000
1.84 1989 Mar 22 (4581) Asclepius 300
1.24 1991 Dec 5 1991 VG 7
0.44 1991 Jan 18 1991 BA 6
0.40 1993 May 20 1993 KA2 6
0.28 1994 Dec 9 1994 XM1 10
0.44 1994 Mar 15 1994 ES1 8
1.92 1994 Nov 24 1994 WR12 200
1.16 1995 Mar 27 1995 FF 20
2.00 1995 Oct 17 1995 UB 10
1.20 1996 May19 1996 JA1 300
1.32 2000 Jun 2 2000 LG6 6

Minimum approach Date of closest approach Object approx diameter
(in lunar distances) (metres)

1.80 1975 Jan. 31 1998 DV9 1,000
1.56 1982 Oct 21 1999 VP11 800 42
42Page 4344
42
4: Objects for which the first orbital calculations indicated that they might impact
Earth during the next 50 years. Further work has dismissed this possibility or made it
improbable. There are nine objects of widely varying size. For three of them (marked * below)
the possibility of impact was dismissed during the month or so after discovery as more observations
were made and their orbits more accurately determined. For two of them (marked **, above and
below) intervening close approaches (see list 3 above) did not allow current observations to
eliminate the possibility of a later impact; fortunately, an impact was eliminated following the
recognition of observations on old photographs (which existed because these objects are large and
therefore bright). In the four remaining cases at least two would probably be too small to do
damage. For the other two the available observations are yet to be performed to allow an impact to
be dismissed. However, even before that, the chances of the object 1998 OX4 hitting the Earth is
thought to be only about 1 in 2,000,000, and the much smaller object 1995 CS, 1 in 200,000.The
objects are arranged in order of earliest possible impact date.

3: Objects 200 metres and larger that have been seen more than once and are predicted
to pass within four lunar distances over the next hundred years. In addition there are
several predicted possible approaches by objects seen only once, although none of them should
come within two lunar distances.

Minimum approach Date of closest approach Object approx diameter
(in lunar distances) (metres)

1.04 2027 Aug 7 1999 AN10 ** 1,000
2.52 2028 Oct 26 1997 XF11 ** 2,000
3.20 2060 Feb 14 (4660) Nereus 900
2.20 2060 Sep 23 1999 RQ36 300
2.64 2069 Oct 21 (2340) Hathor 600
2.36 2086 Oct 21 (2340) Hathor 600
3.52 2095 Apr 9 1998 SC15 500

object approx diameter theoretical [possible] comments
(metres) impact dates

1991 BA 10 2003, 2010, 2046 would be destroyed by atmosphere
1998 OX4 200 2014, 2038, 2044, 2046 not yet dismissed, see text
2000 BF19 * 500 2022 dismissed Feb 2000 by new
observation
1994 GV 10 2036, 2039, 2044, 2050 would be destroyed by atmosphere
1997 XF11 ** 2,000 2040, etc dismissed Mar 1998 by old
observation in archives
2000 EH26 * 200 2041 dismissed Apr 2000 by new
observation
1995 CS 40 2042 small object; not yet dismissed,
see text
1999 RM45 * 500 2042, 2050 dismissed Oct 1999 by new
observation
1999 AN10 ** 1,000 2044, etc. dismissed July 1999 by old
observation in archives

Annex B Impacts and close approaches of Asteroids and Comets 43
43Page 4445
43
Annex C
telescopes and radars
Ground-based GROUND-BASED
TELESCOPES AND RADARS
C-1: Main telescopes and radars used for NEO work
Group Objective Facilities
(country)

LINEAR (Lincoln Laboratory Near survey Two 1 metre US Air Force telescopes; each of the ground-Earth
Asteroid Research) (USA) based Electro-Optical Deep Space
Surveillance (GEODSS)-type www. ll. mit. edu/ LINEAR
controlled by MIT site:
New Mexico, USA

NEAT (Near Earth Asteroid survey 1.2 metre US Air Force telescope on Maui, Hawaii
Tracking) controlled by JPL, follow up (commissioned early 2000)
Pasadena sites: Maui, Hawaii and (USA) 1.2 metre Schmidt telescope at Mt Palomar, California (being
Mt Palomar, California upgraded also to use the NEAT camera)
huey. jpl. nasa. gov/~ spravdo/ neat. html

Spacewatch survey 0.9 metre telescope of Steward Observatory, Arizona;
controlled by University of Arizona follow up 1.8 metre telescope will be fully commissioned by 2001
site: Kitt Peak, Arizona (USA) www. lpl. arizona. edu/ spacewatch/

LONEOS (Lowell Observatory survey 0.6 metre telescope, in full operation early 2000
Near Earth Object Search) (USA) www. lowell. edu/ users/ elgb/ loneos_ disc. html
controlled by Lowell Observatory
site: Flagstaff, Arizona

Catalina Sky Survey survey 0.4 metre telescope; to be replaced by 0.7 metre telescope in
controlled by University of Arizona (USA) Autumn 2000
site: Kitt Peak, Arizona Possible modification and use of 0.6 metre telescope in
Australia, (Southern Hemisphere Survey)
www. lpl. arizona. edu/ css

Southern Hemisphere Survey survey 0.6 metre Uppsala Southern Schmidt Telescope in Australia;
controlled by University of Arizona (USA/ it is hoped that modifications can be financed for use of this
and Australian National University Australia) telescope from 2001
site: Siding Spring, Australia www. lpl. arizona. edu/ css

Arecibo astrometry Planetary radar, 300 metre antenna
controlled by Cornell University; gross structure www. naic. edu
involving JPL for NEOs (USA)
site: Puerto Rico

Goldstone Solar System Radar astrometry Planetary radar, 70 metre antenna
controlled by JPL gross structure echo. jpl. nasa. gov
site: Goldstone, California (USA) 44
44Page 4546
44
C-1: Main telescopes and radars used for NEO (continued)
Group Objective Facilities
(country)

DLR Planetary Radar follow up Planetary radar, 30 metre antenna. Uses radar
controlled by the Institute of (Germany transmitters in Russia and USA
Planetary Exploration (DLR), with USA/ pentium. pe. ba. dlr. de/ ourgroup/ radar. htm
Germany Russia)
Site: Weilheim, Upper Bavaria

Bisei Spaceguard Centre survey 0.5 metre telescope currently in use (for NEO search and
controlled by Japanese Spaceguard follow up for tracking space debris)
Association with National Space (Japan) 1 metre telescope near completion
Development Agency, the neo. jpl. nasa. gov/ missions/ jsga. html
National Aeronautic Laboratory,
and the Science & Technology
Agency site: Bisei, Japan

OCA-DLR Asteroid Survey survey Pending
controlled by (France/ 0.9 metre Schmidt telescope (Since April 1999 this
Observatoire de la Côte d'Azur Germany) observing programme has been discontinued)
(OCA), France and the Institute earn. dlr. de/ odas/ odas. htm
of Planetary Exploration (DLR),
Germany
site: North of Cannes, France

KLENOT (Klet observatory Near follow up 0.57 metre and 0.63 metre telescopes
Earth and Other unusual object (Czech 1.02 metre telescope being built
Team) Republic) www. klet. cz
controlled by Klet Observatory
site: Mt Klet, Czech Republic

Annex C Ground Based Telescopes and Radars 45
45Page 4647
45
C-2: Other telescopes mentioned in report
Group Objective Facilities
(country)

UKST (UK Schmidt Telescope) survey 1.2 metre Schmidt
site: Siding Spring, Australia; All-sky survey plate archive in Edinburgh record earlier NEO
Anglo Australian Observatory sightings; UKST used for Anglo-Australian
Near-Earth Asteroid Survey in 1990s
www. aao. gov. au

AAT (Anglo-Australian Telescope) follow up 3.9 metre telescope
site: Siding Spring, Australia; spectroscopy www. aao. gov. au
Anglo Australian Observatory (Australia, UK)

WHT (William Herschel Telescope) follow up 4.2 metre telescope
site: La Palma, Canary Islands spectroscopy www. ing. iac. es
(UK, Europe)

INT (Isaac Newton Telescope) follow up 2.5 metre telescope
site: La Palma, Canary Islands spectroscopy www. ing. iac. es
(UK, Europe)

JKT (Jacobus Kapteyn Telescope) follow-up 1 metre telescope
site: La Palma, Canary Islands (UK, Europe) www. ing. iac. es

VISTA (Visible and Infrared survey 4 metre primary feeding two alternate wide field cameras
Survey Telescope for Astronomy) follow up First surveys to be completed within 12 years.
UK owned spectroscopy about 25 per cent of time available by peer reviewed
site: ESO's Paranal, Chile (UK) application
www-star. qmw. ac. uk/~ jpe/ vista

6.5 metre, NSF survey telescope survey
(in proposal phase) (USA) www. nsf. gov/ mps/ ast/ strategicplan/ instr. htm

NEO Taskforce Report 46
46Page 4748
46
Annex D
missions
Space-based SPACE-BASED
MISSIONS
D-1: Flyby or rendezvous with asteroid or comet
Mission Objective Encounters and website
(1= primary, etc.)

ICE previously called International Sun comet Giacobini-Zinner: pass through tail,
International Cometary Earth Explorer, ISEE-3. 1985
Explorer NASA 1. science of Sun; comet Halley: distant flyby, March 1986
launched 1978 2. to pass through tail of a comet and stardust. jpl. nasa. gov/ comets/ ice. html
measure its plasma and magnetic features

VEGA-1 and 2 1. probe surface of Venus; comet Halley: close approaches by Vega 1
Russian Space Agency 2. fly both spacecraft near comet Halley and Vega 2, March 1986
launched 1984 and return images www. iki. rssi. ru/ pe. html

GIOTTO 1. study Halley's comet by remote imaging comet Halley: close approach, March 1986
ESA and analysing dust in coma. Closest comet Grigg-Skjellerup: close approach
launched 1985 approach less than 600 kilometres; 1992
2. flyby comet Grigg-Skjellerup sci. esa. int/ home/ giotto/ index. cfm

SAKIGAKE and SUISEI 1. engineering tests; www. isas. ac. jp/ e/ enterp/ missions/ index. html
(2 missions) 2. fly by comet Halley to observe
ISAS, Japan interactions with solar wind
launched 1985

GALILEO 1. rendezvous with Jupiter and its moons, asteroid Gaspra: flyby, 1991;
NASA 1995; asteroid Ida: flyby, 1993;
launched 1989 2. fly by two asteroids observed Comet Shoemaker-Levy 9's
impacts on Jupiter, 1994
www. jpl. nasa. gov/ galileo

Clementine 1. map Moon; mapped Moon 1994
DOD/ NASA nsdc. gsfc. nasa. gov/ planetary/ clementine. html
launched 1994 2. visit Earth-crossing asteroid 1620
Geographos (but booster failed)
[Clementine 2 planned but on hold]

NEAR (Near Earth 1. rendezvous with asteroid Eros; determine asteroid Mathilde: flyby, 1997;
Asteroid Rendezvous) physical and geological properties, and asteroid Eros: flyby, early 1999;
NASA measure elemental and mineralogical asteroid Eros: rendezvous, February 2000
launched 1996 composition near. jhuapl. edu

DEEP SPACE 1 1. demonstrate new technologies; asteroid Braille: flyby, July 28 1999
NASA 2. determine physical properties and Comet 19 Borelly; September 20 2001
launched 1998 measure elemental, mineralogical nmp. jpl. nasa. gov/ ds1
composition of asteroid Braille;
3. extended mission to fly by a comet 47
47Page 4849
47
D-1: Flyby or rendezvous with asteroid or comet (continued)
Mission Objective Encounters and website
(1= primary, etc.)

STARDUST 1. fly probe to within 100 kilometre comet Wild-2: encounter, 2004;
NASA of comet Wild-2's nucleus; June 2004; Sample return, 2006
launched Feb 1999 2. interstellar dust collection en route stardust. jpl. nasa. gov
(2000 and 2002); nucleus imaging,
compositional analysis of particulates,
capture dust particles from coma and
return for analysis

CONTOUR 1. images and comparative spectral maps comet 2 Encke: flyby, 2003;
(Comet Nucleus Tour) of at least three comet nuclei; analyse comet Schwassmann-Wachmann-3:
NASA collected dust samples flyby, 2006;
for launch 2002 comet d'Arrest: flyby, 2008
www. contour2002. org

MUSES-C 1. rendezvous with the potentially asteroid 1998 SF36: rendezvous, 2005
(Mu Space Engineering hazardous asteroid 1998 SF36; deliver www. muses-c. isas. ac. jp
Spacecraft C) ISAS, Japan nano-rover to surface for in-situ imaging, www. isas. ac. jp/ e/ enterp/ missions/ index. html
for launch 2002 collect samples of asteroid; return to Earth
for analysis

NEAP 1. asteroid Nereus; asteroid Nereus
(Near-Earth Asteroid 2. first non-governmental deep space www. spacedev. com/
Prospector) mission
Space Dev Corporation
Possible launch 2001

ROSETTA 1. rendezvous with comet Wirtanen; asteroid Otawara: flyby, 2006;
ESA 11 months of near comet operations; asteroid Siwa: flyby, 2008;
for launch 2003 deliver surface science package to perform comet Wirtanen, rendezvous, 2011
in-situ analysis; sci. esa. int/ home/ rosetta/ index. cfm
2. visit two asteroids on the 8-year journey

DEEP IMPACT 1. internal structure of a comet; Comet Tempel 1: collision encounter, 2005
NASA impact comet with 500 kilogramme copper www. ss. astro. umd. edu/ deepimpact
for launch 2004 projectile; observe debris with spacecraft
camera and spectrometer (and from Earth)

PLUTO-KUIPER EXPRESS 1a. study Pluto and its moon, Charon; Pluto encounter: 2012 to 2020;
NASA 1b. radio science experiment; solar then through EdgeworthÐ Kuiper belt of
for launch 2004 occultation spectrometer and various comets
imagers; www. jpl. nasa. gov/ ice_ fire
2. one or more EdgeworthÐ Kuiper Belt
object flyby

BEPI-COLOMBO 1. study planet Mercury;
ESA planned for launch 2. possible NEO search en-route with sci. esa. int/ home/ bepicolombo/ index. cfm
in or after 2009 imaging cameras

DEEP SPACE 4 1a. test 20 new technologies;
NASA 1b. land on nucleus of active comet;
(to be confirmed) possible sample return

NEO Taskforce Report 48
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Annex D Space-based missions
D-2: Missions with space telescopes
Mission Objective Encounters and website
(1= primary)

HST space telescope (aperture 2.4 metres);
Hubble Space Telescope optical and ultra violet wavelengths www. stsci. edu
NASA/ ESA
launched 1990

SOHO 1. study Sun's internal structure (keeping > 100 comets discovered, mostly Sun-grazers
ESA/ NASA in orbit 1.5 million kilometre sun-ward sohowww. nascom. nasa. gov
launched 1995 of Earth for uninterrupted view of Sun),
various imagers;
2. inadvertently detects many comets

SIRTF 1. infra-red space telescope
Space based Infrared (aperture 0.85 metres) sirtf. jpl. nasa. gov
Telescope Facility may detect many asteroids based on
NASA experience from previous missions
for launch 2001

SWIFT 1. study gamma-ray bursts; asteroids will be detected as 'noise' to
NASA burst -alert telescope; X-ray telescope; the primary data
for launch 2003 ultraviolet/ optical telescope swift. sonoma. edu

NGST large space telescope (aperture ~8 metres) www. ngst. stsci. edu
Next Generation Space (primarily infrared)
Telescope proposals being studied
NASA, ESA, Canada
proposed launch 2007

GAIA 1. measure positions of distant stars sci. esa. int/ home/ gaia/ index. cfm
ESA (1-metre class telescopes);
planned for launch in or 2. predicted also to discover NEOs down
after 2009 to about 500 metres. 49
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G l o s s a ry
albedo: a measure of an object's reflecting power;
the ratio of the amount of light scattered by a body
to the incident light.

amor: an asteroid with an orbit always exterior to
the Earth's, but interior to that of Mars.

aphelion: the point at which an object in orbit
around the Sun is furthest from it.

apollo: an asteroid with an orbit that lies mostly but
not entirely outside that of the Earth; its orbit may
cross that of Earth.

asteroid: a minor planet; a body of rock, carbon, or
metal orbiting the Sun. Most asteroids occupy the
Main Belt between the orbits of Mars and Jupiter.
The largest asteroid is Ceres, diameter 950
kilometres, and the size of asteroids ranges down to
countless numbers of boulders.

astronomical unit, or AU: the average distance
between the Earth and the Sun; about 150 million
kilometres.

aten: an asteroid with an orbit that is mostly interior
to that of the Earth; its orbit may cross that of Earth.

comet: a body of dust and ice in orbit about the
Sun. As it approaches the Sun it may develop a
"fuzzy" head and a tail from the gas and dust ejected
from the nucleus.

CCD: a "charge-coupled device"; an electronic
detector sensitive to visible or infrared light, giving a
signal that can generate a digital image as in a TV
camera. CCDs require powerful computers to
analyse and display the data.

Earth crossing asteroid [or comet]: an asteroid
[or comet] whose orbit crosses that of the Earth if
viewed from the pole of the Earth's orbit; the
asteroid [or comet] may pass above or below the
Earth's orbit.

EdgeworthÐ Kuiper Belt: a region beyond the
orbit of Neptune extending to around 1,000 AU
from the Sun and containing perhaps a billion
objects; the source of short-period comets.

electromagnetic spectrum: the range of all
wavelengths emitted or absorbed by matter, including
not only visible light, but infrared and radio at longer

wavelengths and ultraviolet, X-rays and gamma rays
at shorter wavelengths; analysis of the spectrum is the
main way that astronomers gain insight into the
nature of astronomical bodies.

giant planets: the four outer planets in the solar
system: Jupiter, Saturn, Uranus and Neptune. These
planets are very massive, of great size, yet of low
density compared to the inner or terrestrial planets
Mercury, Venus, Earth and Mars. The giant planets
have no solid surface, being composed mainly of
hydrogen, while the terrestrial planets have rocky
surfaces.

infrared radiation: light at wavelengths beyond the
red part of the spectrum, to which our eyes do not
respond. Much infrared radiation falling on the Earth
is stopped in the atmosphere, so infrared telescopes
must be in orbit or on the tops of high mountains.

K/ T boundary: the Cretaceous-Tertiary boundary,
that is the boundary between groups of geological
strata, signifying a global climatic change some 65
million years ago. The K/ T event is whatever caused
this global change, and is identified with the asteroid
impact that caused the Chicxulub crater.

light year: the distance travelled by light in free
space in one year; about 100 billion kilometres, or
about 60 thousand AU. The nearest star to the Sun is
about four light years distant.

long-period comet: a comet with an orbital
period longer than 200 years; such comets are
thought to originate in the Oort Cloud, and can
approach the Sun from any direction.

lunar distance: the average distance from
Earth to Moon: 384,400 kilometres,
0.00256955 Astronomical Units (AU) or about
1.3 light seconds.

magnitude: a measure of the brightness of
astronomical objects; the smaller the number the
brighter the object. A difference of 5 magnitudes
corresponds to a change in brightness of 100 times.

meteor: the bright streak of light Ð a "falling star"Ð
that occurs when a solid particle from space (a
meteoroid) enters the atmosphere and is heated by
friction. 50
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NEO Taskforce Report
meteorite: a solid body that partly survives the
passage through the Earth's atmosphere, and reaches
the Earth's surface.

near Earth asteroid: an asteroid whose distance
from the Sun at perihelion is less than 1.3 AU.

near Earth comet: a comet whose distance from
the Sun at perihelion is less than 1.3 AU.

Near Earth Object (NEO): a near Earth asteroid
or a near Earth comet.

Oort Cloud: a sphere around the Sun, extending to
about two light years in radius, filled with a huge
number (more than a thousand billion) of cometary
nuclei that are the remnants of the formation of the
solar system. Passing stars are thought to perturb
objects from the Cloud, and cause the long-period
comets.

perihelion: the point at which an object in orbit
around the Sun is closest to it.

potentially hazardous asteroid: an asteroid of at
least 150 metres diameter, with an orbit that is
within 0.05 AU of the Earth's orbit.

radar: active sensing of an object using a beam of
radio waves directed at the object; the detection of
the reflected radiation from an asteroid or planet can
give information about position, velocity, rotation,
and morphology.

short-period comet: a previously detected comet,
with period less than 200 years; such comets tend to
approach in the plane that contains the planets, are
thought to originate in the Kuiper Belt, and their
orbits are subject to perturbation by the planets.

spectroscopy: the analysis of radiation, and
inference of its source, by splitting the radiation up
into its constituent wavelengths.

tsunami: a deep water wave generated in the ocean
at the site of an earthquake, underwater landslip, or
asteroid impact; a tsunami amplifies and breaks when
it runs into shallows; incorrectly known as a tidal
wave.

visible light: that part of the electromagnetic
spectrum to which our eyes respond. 51
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51
In the chapters of this report references are only given for each
Table and Graph. For the craters in Annex B-1, references are
given at the end of this Bibliography. Annexes C and D
themselves include names of relevant websites. Otherwise,
reference should be made to the books, papers and web sites
listed below.

Books Bailey ME, Clube SVM & Napier WM, The origin of comets,
Pergamon Press, 1990,
ISBN 0-08-034858-0

Gehrels T (Ed), Hazards due to Comets and Asteroids, University
of Arizona Press, 1994, ISBN 0-8165-1505-0 This covers all
aspects of NEOs, comprehensively.

Lewis JS, Comet and Asteroid Impact Hazards on a Populated
Earth, Academic Press (includes software disk allowing random
simulations of impactor flux to Earth and consequent deaths
occurring). 2000.
ISBN 0-12-44760-1

Lewis JS, Rain of Iron and Ice, Reading, Mass, Addison-Wesley,
1996

Spencer JR & Mitton J, The great comet crash, Cambridge
University Press 1995, ISBN 0-521-48274-7

Steel D, Rogue Asteroids and Doomsday Comets, John Wiley and
Sons Inc, 1995, ISBN 0-471-30824-2; 1997, ISBN 0-471-
19338-0

Thomas PJ (Ed), Chyba CF & McKay CP, Comets and the
Origin and Evolution of Life, Springer-Verlag, 1997

Papers and articles Ball, DJ & Floyd, PJ (1998) Societal Risks; Research Report,
available from Risk Assessment Policy Unit, Rose Court, 2
Southwark Bridge, London SE1 9HS

Binzel RP, et al (1999) From the Pragmatic to the Fundamental:
The Scientific Case for Near-Earth Object Surveys, Report
prepared for Astronomy and Astrophysics Survey Committee of
National of the National Academy of Sciences, 10 May 1999

Binzel RP, (2000) The Torino Impact Scale, Planetary and Space
Science, 48, 297

Canavan, G H (1994), What can we do about it? AAAS Meeting,
San Francisco, February 1994

Canavan, G H (1995), Cost and Benefits of NEO Defences,
Planetary Defence Workshop, 1995, see also T Gehrels' book,
above

Chapman & Morrison (1994), Impacts on the Earth by asteroids
and comets: assessing the hazard, Nature, 367, 33

Clube SVM, Hoyle F, Napier WM, & Wickramasinghe NC
(1996), Giant Comets, Evolution and Civilisations, Astrophysics
& Space Science, 245, 42

Council of Europe, study (1996) Report on detection of asteroids
etc, Council of Europe: Doc. 7480, 9 February 1996 Council of
Europe: reference motion 1080

European Space Agency's Operations Centre (ESOC) (1997),
Study of a global network for research on NEOs, ESOC Contract
No. 12314/ 97, European Space Agency,
www. esa. int/ gsp/ (Applications then Page reference 97/ A10)

ESOC study (2000); Spaceguard Integrated System for Potentially
Hazardous Object Survey, Carusi et al, ESOC Contract No.
13265/ 98 with report ref D/ IM, SGF/ Pr# 2/ Doc-05, 28 April
2000. www. esa. int/ gsp/ (Applications then Page reference
98/ A15)

Gehrels T (1996) Collisions with Comets and Asteroids, Scientific
American, 274, No 3, p34

Grintzer C, (1998) The NEO Impact Hazard and options for
mitigation, EUROSPACE Technische Entwicklung GmbH,
Potsdam, Germany.

Harris, Alan W (1998a), Evaluation of ground-based optical
surveys for NEOs, Planet & Space Sci. 46, 283

Harris, Alan W (1998b), Searching for NEAs from Earth or
Space, Highlights of Astronomy, 11A, 257 (Ed: J Andersen for
IAU).

Health and Safety Executive (1999): Reducing Risks, Protecting
People, Discussion Document. Available from Jean Le Guen,
Risk Assessment Policy Unit, Rose Court, 2 Southwark Bridge,
London SE1 9HS

Holloway NJ (1997) Tolerability of Risk from NEO impacts,
Spaceguard meeting at Royal Greenwich Observatory, 10 July
1997

Jewitt, D (2000), Eyes Wide Shut, Nature 403, 145
Johnson-Freese J & Knox J (2000) Preventing Armageddon: Hype
or Reality, JBIS, 53, 173

Lissauer JJ (1999) How common are habitable planets? Nature,
402, p C11, Supp, 2.12.99

Morrison D & Chapman C (1995) The Biospheric hazard of
large impacts, Proceedings of Planetary Defence Workshop, 1995

POST Report 81, Safety in Numbers, Parliamentary Office of
Science and Technology, UK, June 1996

POST Report 126, Near Earth Objects, Parliamentary Office of
Science and Technology, UK, April 1999

Rabinowitz D, Helin E, Lawrence K & Pravdo S (2000)
Reduced estimate of the number of kilometre-sized near-Earth
asteroids, Nature, 403, 165

Solem JC (2000) Deflection and Disruption of Asteroids on
Collision Course with Earth, JBIS, 53, 180

Steel, D et al (1997), Anglo-Australian Near-Earth Asteroid
Survey: Valedictory report, Aust. J. Astr. 7 (2): 67

B i bl i og raphy (a n d we b s i t e s ) 52
52Page 5354
52
Bibliography (and websites)
Urias JM et al (1996) Planetary Defence: Catastrophic Health
Insurance for Planet Earth Research Paper presented to "USAF
2025",
www. fas. org/ spp/ military/ docops/ usaf/ 2025/ v3c16/ v3c16-
1. htm# Contents

van den Bergh, S (1994) Astronomical Catastrophes in Earth
History, Publications of the Astronomical Society of the Pacific,
106, July 1994

Ward S & Asphaug E (2000a) Asteroid Impact Tsunami Ð a
Probabilistic Hazard Assessment, submitted to Icarus

Ward S & Asphaug E (2000b) Impact Tsunami Ð Eltinan,
submitted to Deep Sea Research Ð Oceanic Impacts, 7 June 2000

Yeomans, D (2000) Small bodies of the Solar System,
Nature, 404, 829

US Congressional Hearings and Reports for Congress
Rather JDG, Rahe JH & Canavan G, Summary report of the
Near Earth Object Interception Workshop, sponsored by NASA
headquarters and hosted by the Los Alamos National Laboratory,
August 31, 1992

Proceedings of the Near-Earth Object Interception Workshop (eds.
Canavan GH, Solem JC & Rather JDG), Los Alamos National
Laboratory, New Mexico, USA, LA-12476-C (1993)

Morrison D (chair) (1992), The Spaceguard Survey, Report of
NASA International Near-Earth-Object Detection Workshop,
January 1992 (Jet Propulsion Laboratory and California Institute
of Technology) prepared for NASA Office of Space Science and
Technology

Shoemaker E (Chair) et al (1995), Report of Near-Earth Objects
Survey Working Group, Office of Space Science, NASA

UN Publications General Assembly Resolutions and International Treaties Pertaining
to the Peaceful Uses of Outer Space, United Nations Office for
Outer Space Affairs, www. oosa. unvienna. org/ treat/ treat. html

Near-Earth Objects Ð The United Nations International
Conference, Proceedings, J Remo (Ed), New York Academy of
Sciences, ANYAA9 822 1-632, 1997

Report of the Third United Nations Conference on the Exploration
and Peaceful Uses of Outer Space, United Nations Publication
A/ CONF. 184/ 6,Vienna, July 1999, Resolution I. 1. c. i, iii and iv

NEO Search Groups and other useful NEO websites,

a selection NASA/ Jet Propulsion Lab: Solar Systems Dynamics Site:
ssd. jpl. nasa. gov

Near Earth Object Program: neo. jpl. nasa. gov
Near Earth Asteroid Tracking:
huey. jpl. nasa. gov/~ spravdo/ neat. html

NASA/ Ames Research Centre: space. arc. nasa. gov
astrobiology. arc. nasa. gov

Asteroid Fact Sheet, NASA/ Goddard Pages
nssdc. gsfc. nasa. gov/ planetary/ factsheet/ asteroidfact. html

Minor Planet Center:
cfa-www. harvard. edu/ iau/ mpc. html

Minor Planet Ephemeris Service,
cfa-www. harvard. edu/ iau/ MPEph/ MPEph. html:

NEO Confirmation Page :
cfa-www. harvard. edu/ iau/ NEO/ ToConfirm. html:

LINEAR: www. ll. mit. edu/ LINEAR/
LINEAR: Project's sky coverage plots,
www. ll. mit. edu/ LINEAR/ skyplots. html

NEAT: neat. jpl. nasa. gov
Spacewatch Project: www. lpl. arizona. edu/ spacewatch/
Catalina Sky Survey: www. lpl. arizona. edu/ css/
LONEOS: www. lowell. edu/ users/ elgb/ loneos_ disc. html
asteroid. lowell. edu/

The Planetary Society: planetary. org/
International Astronomical Union (IAU): www. iau. org
European Asteroid Research Node (EARN):
www. astro. uu. se/ planet/ earn/

Uppsala observatory: www. astro. uu. se
Armagh Observatory: www. arm. ac. uk
Society for Interdisciplinary Studies
www. knowledge. co. uk/ xxx/ cat/ sis/

Spaceguard, UK: ds. dial. pipex. com/ spaceguard/
Spaceguard Foundation: spaceguard. ias. rm. cnr. it/ SGF/
Spaceguard Central Node,
spaceguard. ias. rm. cnr. it/ index. html

Near Earth Object Dynamics Site, NEODyS:
newton. dm. unipi. it/ cgi-bin/ neodys/ neoibo

Riskpage website, Pisa: newton. dm. unipi. it/ cgi-bin/
neodys/ neoibo? riskpage: 0; main

Spaceguard, Australia: www1. tpgi. com. au/ users/ tps-seti/
spacegd. html

Spaceguard, Canada: www. spaceguard. ca/?
Klet Observatory: www. klet. cz/ foll. html 53
53Page 5455
Space Protection of the Earth, Third International Conference,
11Ð 15 September, 2000, Evpatoriya, Crimea, Ukraine:
www. snezhinsk. ru/ spe2000/

References to major impacts listed in Annex B-1
[1, 4, 7, 12] Impact Craters on Earth, NASA pages
observe. ivv. nasa. gov/ nasa/ exhibits/ craters/ impact_ master. html

[2, 5, 6, 9, 13, 14] Terrestrial Impact Craters, Views of the Solar
System, CJ Hamilton
www. solarviews. com/ eng/ tercrate. htm

[5] Aorounga Craters
www. jpl. nasa. gov/ radar/ sircxsar/ chad2. html

[3] Killer Crater Found, Discovery. com news pages, Larry
O'Hanlon,
www. discovery. com/ news/ briefs/ 20000419/ geology_ crater. html

[8] Collisions with Comets and Asteroids, T Gehrels, Scientific
American, Vol 274, No 3, March 1996, p34; more on Chicxulub:
planetscapes. com/ solar/ raw/ earth/ chicxulb. gif;
www. jpl. nasa. gov/ radar/ sircxsar/ yucatan. html

[10] Chesapeake Bay: marine. usgs. gov/ fact-sheets/ fs49-98/
[11] Roter Kamm, Namibia:
southport. jpl. nasa. gov/ pio/ srl1/ sirc/ srl1-roterkamm. gif

[16] Rain of Iron and Ice, Lewis, JS, Helix Books ISBN: 0-201-
48950-3

[17] Wabar Craters,
www. sciam. com/ 1998/ 1198issue/ 1198wynn. html

[18] Tunguska Homepage, University of Bologna pages, Guiseppe
Longo www-th. bo. infn. it/ tunguska/

[19, 20,] Spaceguard UK Report,
ds. dial. pipex. com/ town/ terrace/ fr77/ more. htm

[21] Comet Shoemaker-Levy 9 Collision with Jupiter, NASA
Goddard pages, JH King
nssdc. gsfc. nasa. gov/ planetary/ comet. html

[22] Eltanin R Grieve in Ann NY Acad Sci, vol 822, p. 338,
1997; Kyte et al New evidence on the size and possible effects of a
late Pliocene oceanic impact, Science, 241, 63Ð 65, 1988. Papers by
Ward S & Asphaug, see Papers and Articles, above

53

Bibliography (and websites) 54
54Page 5556
54
Moon impact craters and Earth.
Image courtesy of NASA.
Title page

Orbits of all near Earth asteroids.
Image courtesy of Scott Manley (Armagh
Observatory) and Duncan Steel (University of
Salford).
Page 9

Barringer Crater, Arizona.
Image courtesy of NASA.
Page 10

Asteroid Eros from orbiting spacecraft.
Image courtesy of NEAR/ NASA.
Page 11

Orbits of Aten, Apollo and Amor.
Courtesy of David Asher.
Page 12

Asteroid belt within Jupiter's orbit.
Image courtesy of NASA/ JPL.
Page 12

Comet Hale-Bopp above Stonehenge.
Paul Sutherland, Galaxy Picture Library.
Page 13

Orbits of Halley's comet and Hale-Bopp.
Courtesy of David Asher.
Page 13

Comet Shoemaker-Levy 9 hitting Jupiter, 1994.
Image courtesy of NASA.
Page 15

Asteroid and comet impact craters on far side of
Moon.
Image courtesy of NASA.
Page 17, Inside front and back covers

Eltanin impact.
Courtesy of Steven Ward and Eric Asphaug,
University of California, Santa Cruz.
Page 18

Clearwater Lakes.
Image courtesy of NASA.
Page 19

Observation of near earth object.
Image courtesy of James V. Scotti (observer),
©( 1997) Arizona Board of Regents.
Page 23

1 metre telescope, of LINEAR.
Reprinted with permission of MIT Lincoln
Laboratory, Lexington, Massachusetts.
Page 26

1.2 metre United Kingdom Schmidt Telescope.
© 1982, UK ATC, Royal Observatory, Edinburgh
Page 27

NASA's Deep Impact mission.
Image courtesy of Ball Aerospace & Technologies
Corp.
Page 29

Acknow l e d ge m e n t s f o r I l l u s t rat i o n s 55
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For further information visit:
http:// www. nearearthobjects. co. uk

Information Unit
British National Space Centre
151 Buckingham Palace Road
London
SW1W 9SS

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