Meeting report
T
he Geological Society rooms were brimming on 14 December 2001, not only
with Fellows but also numerous guests.
The latter represented the British Interplanetary
Society, the Planetary Society and the mass
media, plus the European Space Agency and the
United Nations Office for Outer Space Affairs.
Obviously something unusual was afoot.
The government and public support science
because they anticipate that something positive
and useful will derive from such research. This
may be a novel invention or new knowledge;
thus economic gains, enhanced quality of life,
and national prestige.
Science also delivers positives through double
negatives. Forensic science leads to a positive
by helping reduce crime, while medical
research produces positives by alleviating disease: both double negatives. Studies of nearEarth objects (NEOs) can do likewise.
By identifying the next potential NEO impact
we can ameliorate its effects, or maybe obviate
it altogether. But lots of warning time is needed and that is where astronomy comes in. We
must scour the skies, catalogue all Earthapproaching asteroids above a certain size and
see whether one has our number on it. We
must do this soon. The dinosaurs could not see
their doom coming, but we can.
Multifarious aspects
The meeting began with Duncan Steel (Salford
University) describing reasons for investigating
NEOs. Asteroids and comets are of interest to
us in their own right. Each represents a little
world worthy of exploration.
Over the next decade space probes will visit a
clutch of NEOs. If we are to decipher the
cratered surfaces of planets and moons, we
must understand the projectiles shaping them.
Impacts on the Moon and Mars have delivered
us free samples – lunar and martian meteorites
– and so may be involved in panspermia. NEOs
have been central in the Earth’s evolution, both
geologically and biologically. To understand
debris disks around distant stars, what we see
orbiting our own star must first be explained.
Finally, when humankind starts to colonize
space, the best source of raw materials will be
NEOs, composed of metals, rock, organic
chemicals and water. NEOs, then, provide
many opportunities for all UK astronomy and
space science, the general theme of the meeting.
Telescopic views
The first five papers addressed remote observations, each in a different way. Alan Fitzsimmons (Queen’s University Belfast) reviewed
present UK ground-based capabilities for NEO
study. Although with the joining of ESO the
suite of UK telescopes will change, current
instrumental assets could make vital contributions to NEO monitoring. For example, at pre1.14
1: Spatial density of known asteroids in the inner solar system. Although most are in the main belt,
there are many Earth-approaching asteroids (by Scott Manley from Target Earth by Duncan Steel).
Bringing NEOs
into focus
Duncan Steel and Mark Bailey report on the well-attended December 2001
G Discussion Meeting whose subject was near-Earth objects.
sent the sizes of NEOs found by US search
teams can only be estimated crudely from their
brightnesses, but individual albedos and hence
sizes could be determined using UKIRT.
NEO search systems differ from conventional telescopes because the targets traverse the
sky quickly, typically at one degree per day.
Rapid coverage of wide areas to faint limiting
magnitudes is needed, but long integration
times gain nothing. Peter Wheatley (Leicester
University) described the Wide-field Automated Survey Programme (WASP). This comprises
four off-the-shelf camera lenses imaging a tendegree field onto CCD detectors, reaching
magnitude 16 with 30-second exposures. The
anticipated data rate is huge, several terabytes
per year; many small NEOs passing close by
the Earth should be found.
Telescopic study was one of several aspects of
NEO research at the Open University summarized by John Zarnecki. Others include investigations of lunar crater morphologies rendering
impactor directions (detailed in a poster by
David Wallis), a proposed fireball camera network in Western Australia to identify meteorite-dropping events, and the ATLAS proposal. The latter, involving several UK groups,
aims to discover and explore NEOs using combined ground- and spaced-based techniques, as
outlined in a poster by Paulo D’Arrigo (Astri-
um Ltd) and others. Zarnecki also described a
satellite proposal entitled SIMONE, involving
researchers from QinetiQ; the target is a primitive NEO (a carbonaceous asteroid).
Sarah Dunkin (RAL) took NEO searches offplanet. The BepiColombo orbiter, arriving at
Mercury in 2012, should carry a 20 cm aperture camera for an asteroid search. Those bodies spending their lives mostly inside our orbit,
the Atens and the suspected apoheles, are difficult to spot. From Mercury we can obtain a
better survey of that NEO population.
Wyn Evans (Oxford University) also examined a space-based search system. The GAIA
mission, for launch in 2010, will conduct a
solar system census, mapping about a thousand
comets and a million asteroids, plus a billion
galactic stars. Because GAIA can look near-sunward, it will also find apoheles, plus the Earth
Trojans which, if they exist, would be the most
accessible objects in space. On the other hand,
GAIA cannot go very faint and so will detect
few asteroids smaller than 1 km in size.
Taking a closer look
From far away, NEO data collection is limited.
To know precisely what we are dealing with we
must get in close. Are NEOs like meteorites, or
something different? Are they mostly monoliths, or rubble piles? Are some asteroids
February 2002 Vol 43
Meeting report
2: The Aorounga crater chain in Chad, on the edge of the Sahara desert, formed by an asteroid or comet
that broke apart shortly before impact (a Space Shuttle radar image; Adriana Ocampo, NASA/JPL).
extinct or dormant comets, or all orphans from
the main belt? To answer such questions we
must conduct a reconnaissance, sending spacecraft to a range of NEOs.
Phil Palmer (Surrey University) described small
satellite missions to NEOs, each costing less
than £15 m including launch. The benchmark
system has a 120 kg wet weight, 20 kg payload,
and solar thermal propulsion with hydrazine
expellant. Short-duration missions of 200–300
days were examined. Potential targets are plentiful, because many NEOs are now known.
Apostolos Christou (Armagh Observatory)
continued the same theme. He showed there to
be hundreds of NEOs with required delta-vees
below those necessary for Venus or Mars missions, some down to 0.2 km/sec. Flight times are
as low as 50 days, with about one launch opportunity per week. Lunar gravitational assists
would reduce the required thrusts, meaning
lower propellant masses and larger payloads.
Several rendezvous (as opposed to fly-by) missions, allowing extended close-up study, were
identified with delta-vees down to 1.4 km/sec.
Past impacts on Earth can tell us much. Iain
Gilmour (Open University) discussed geochemical investigations of terrestrial impact sites
and described the European Science Foundation’s IMPACT programme. This umbrella
involves ways in which our planet (and its
inhabitants) has responded to cataclysmic
impacts; scientists from the biological, geological and other disciplines have been involved,
quite apart from astronomers. Activities focus
on specific workshops held about twice a year
(pssri.open.ac.uk/ESF/).
Additional posters were presented by Catherine Dandy (QUB) and co-workers on the
colours of NEOs; Roger Dymock on UK amateur astronomers’ observational capabilities;
February 2002 Vol 43
Ivan Grey (Kent University) on laboratory
impact experiments; and Duncan Steel (Salford
University) on the Anglo-Australian NearEarth Asteroid Survey.
Responding to the risk
How significant is the NEO impact hazard?
How does it compare with other low-probability, large-consequence risks that people (and
hence governments) take seriously? Here we are
talking about meltdowns of nuclear power
plants like Chernobyl, extreme storms and
tsunamis, phenomenal earthquakes and the like.
Nigel Holloway (a member of Spaceguard
UK), who has expertise in major risk assessments, discussed these questions and showed
that while there are greater individual hazards
(you are more likely to die in a car crash),
NEO impacts rank surprisingly high. The longterm averaged death rate from impacts for the
whole world is about 6000 per year, rather
more than jetliner crashes kill. This greatly
exceeds the expected rates for nuclear reactor
failures, both in terms of individual death
probabilities and also deaths per event, yet we
spend billions on reactor safety and essentially
nothing on identifying dangerous NEOs. Since
global nuclear arsenals were cut back, NEO
impacts remain the only agent capable of
killing billions in a single catastrophe (apart
from, say, a very unlikely nearby supernova).
Benny Peiser (Liverpool JMU) described the
history of asteroid and comet scares in the mass
media. This is not a new phenomenon. In 1910
widespread panic stemmed from warnings that
the Earth would pass through Comet Halley’s
tail, the gullible believing they would be poisoned. More recently impacts have become a
perennial media favourite, not all stories being
solidly based either in the information supplied
to journalists, or the use made of it.
The final major contribution came from
Colin Hicks (Director General, British National Space Centre), who addressed the subject of
government policy and future plans for NEOs.
He began by noting that “there is no doubt
whatsoever that NEOs are dangerous”, and
continued by detailing the recent history of
action by HM Government, including the Task
Force report published late in 2000 and developments thereafter. On the day preceding the
meeting a question was asked in the House of
Commons regarding the implementation of the
NEO Task Force recommendations, the reply
being that news of the next steps would be
made public shortly. The UK has, however,
come forward to lead a United Nations group
looking at international co-ordination of NEO
studies, and in the same respect is playing a
leading role in putting this subject on the agenda within the OECD’s Global Science Forum.
Concluding remarks then followed from
Mark Bailey (Armagh Observatory), before the
meeting adjourned so as to join the monthly
Astronomy and Geophysics Meeting at the Scientific Societies’ Lecture Theatre in Savile Row.
International speakers
To conclude the day’s discussions on NEOs we
were privileged to host two international speakers who gave their talks at the main meeting.
Hans Haubold (UN Office for Outer Space
Affairs, Vienna) spoke on United Nations Initiatives on NEOs, indicating that this subject
has engaged the UN for some years. There was
a specific NEO conference at the UN Headquarters in New York in 1995; the UNISPACE
III conference in 1999 considered the NEO
problem; and in March 2001 the UN co-sponsored a workshop in Seville on the impact hazard. In the future Haubold looked forward to
continued rapid developments, especially with
the UK having agreed to take a leading role.
Marcello Coradini (Coordinator of Solar System Missions, European Space Agency) discussed ESA’s contribution to the understanding
of NEOs and their related problems. As noted
at the start of this report, NEOs catch the headlines largely because of the impact hazard, but
they also represent potential benefits, plus they
deserve scientific study in their own right. ESA
is involved centrally in this work, ranging from
the NEO camera planned for BepiColombo
and the potential of GAIA for surveying asteroids and comets, through to the Rosetta probe
to Comet Wirtanen, due for launch in 2003.
NEOs are an international problem; ESA is taking a pan-European approach to addressing
what needs to be done. ●
Duncan Steel, Joule Physics Laboratory, University
of Salford; Mark Bailey, Director, Armagh Observatory, College Hill, Armagh.
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