Meeting report
A
stronomers representing space
agencies and other groups with
interests in the international
Spaceguard programme met in Turin
from 1–4 June 1999 for the meeting
“International Monitoring Programs
for Asteroid and Comet Threat
(IMPACT)”. Plenary sessions reviewed
current survey programmes and associated scientific and policy issues thrown
up by the recent greatly enhanced discovery rate of Near-Earth Objects
(NEOs); sub-groups hammered out recommendations and procedures for
future implementation. The agreed resolutions will be taken forward with
governments and funding agencies, and
international bodies such as the International Astronomical Union.
Background
Deep
impact
Mark Bailey reports from IMPACT, Turin, 1–4 June.
telescope, operating at the same site,
and is expected to produce a second
step-increase in the rate of discovery.
Lost and found
One of the main themes of the meeting
concerned the question of how to handle the vastly increased number of
asteroid detections, and how to ensure
that the asteroids, once found, are not
subsequently lost due to lack of suitable
follow-up. The MPC, originally set up
to coordinate a moderate rate of discovery of comets and minor planets,
needs additional resources to cope with
the extra demands of an order of magnitude increase in data throughput. A
further factor is the increasing demands
of users of the MPC service, who sometimes require essentially instantaneous
access to new discoveries, rapid computation of orbital data and projections,
and information on where other survey
telescopes are looking, both to maximize the overall survey efficiency and
the chance that an asteroid, once
detected, will not be lost.
Increasingly, it is clear that wide-field
survey programmes able to discover
many so-called “small” solar system
objects should support the desired central facilities, such as the Spaceguard
Central Node and the Minor Planet
Center. A proper survey should also
incorporate the relatively low cost of
follow-up facilities to ensure that initial
detections are not lost.
The IMPACT workshop to review
progress towards establishing an international programme to detect – and if
necessary deflect – any incoming asteroid or comet with the potential to
destroy civilization or threaten life on
Earth, was not the first such meeting. It
followed a meeting on the Mediterranean island of Vulcano in September
1995.
The IMPACT meeting, sponsored by
bodies including the International
Astronomical Union (IAU), the Plane- Mjølnir – Thor’s Hammer – an impact crater 24 miles across in the
tary Society, the Spaceguard Founda- Barentz Sea, shown in a false colour image from seismic data. (F
tion, the Italian Space Agency (ASI), Tsikalas, S T Gudlaugsson, J I Faleide, O Eldholm, Geology, Univ. of Oslo.)
and both NASA and ESA, included representatives from virtually all the orgaWhat are NEOs?
nizations currently carrying out major
work in this area. Six of the seven prinThe second broad area of discussion
cipal observational groups were reprefocused on the programmes necessary
sented, as were all the teams presently
to achieve complete physical characterinvolved in handling the vast increase
ization of the NEO ensemble, both
in orbital data and other information
comets and asteroids. Only by this
for astronomers worldwide.
means can a full understanding of the
The rapid progress in this area is
origin of NEOs be achieved (e.g. the
best illustrated by the success of
respective proportions originating via
the Massachussetts Institute of Techcollisions in the main asteroid belt or
nology/Lincoln Laboratory programme
through the evolution and possible
LINEAR (Lincoln Near Earth Asteroid
break-up of comets). Such information
Research), at the experimental test site
would also be necessary in order to
on the White Sands Missile Range in
deflect such objects prior to possible
Socorro, New Mexico. The Lincoln
impact with the Earth, should our gensurvey, largely funded by the United
eration be both unlucky enough to be
States Air Force, uses a wide-field, A relic of collision on Mimas, photographed by Voyager 1 in 1980 (NASA). alive when a major impact is due and
rapid read-out CCD on a military
lucky enough to discover the projectile
discovered more than 200 of the 700 or so
GEODSS (Ground-based Electro-Optical Deep
before it discovers us.
known NEOs, and has produced – in that time
Space Surveillance) 1 m telescope, capable of
These astronomical programmes require
alone – more than a five-fold increase in the
reaching a limiting magnitude of ~22 on a 2
spectrophotometric observations of asteroids
workload of the IAU Minor Planet Center
square degree field of view in less than 100 secand cometary nuclei with the objective of iden(MPC), representing more than a million astroonds integration time. The system has been
tifying bulk properties of the solid body such
metric observations. The programme will
operating with the wide-field CCD since
as mineralogical composition (e.g. in comparishortly be joined by a second GEODSS
March 1998, in which time it has already
son with interplanetary dust particles,
August 1999 Vol 40
4.25
Meeting report
meteorites or main-belt asteroids), shape, spin
axis, rate of rotation, density, and whether the
structure is monolithic or, possibly more likely,
rubble-pile. These types of observations provide ground truth for the size distribution of
NEOs, their relationship to the planetary
building blocks called planetesimals, and their
respective interrelationships with other members of the Sun’s extended family of small bodies. Such information is also essential if any
NEO is to be deflected.
Access to a wide range of astronomical telescopes in the 2–10 m class will be required over
the next decade to carry out these visual/
infrared programmes, as too will data from
planned space missions over the next few
years. As was pointed out by Don Yeomans
(Director of the NASA/JPL NEO Program
Office), solar system astronomy is now entering a new golden age, with spacecraft going to
13 separate comet or asteroid targets in as
many years. Within this time-frame it is likely
that our knowledge of such small bodies will
go through a revolution as profound as that of
the first phase of solar system exploration,
which resulted, in the late 1960s, in recognition of the extraterrestrial impact hazard in the
first place.
The announcement dilemma
The third, and possibly the most contentious,
focus of the meeting attempted to deal with the
responsibility of astronomers, as professional
scientists and citizens, regarding the collision
hazard. For example, what procedures should
be in place prior to the announcement of a possible impact (e.g. enhanced peer-review), and
then who should be informed, how quickly,
and at what stage should the information be
placed in the public domain and the media
involved? It is obvious that as the present survey programmes get fully into their stride, the
so-called “announcement dilemma” will
become an increasing problem.
Several objects have non-zero probabilities of
impact with the Earth within the next 50–100
years. The values (all low) are likely to be
revised downwards in the light of further
observations, but the number of such cases is
bound to increase.
The difficulty is that whereas premature
announcement might lead to a culture of false
alarms and the accusation of “crying wolf”
(not to mention possible panic amongst vulnerable members of the public), the lack of an
early announcement might lead to a situation
where the warning of a real impact was not
made early enough for effective mitigation.
The media, of course, loves this. Headlines
can almost always be guaranteed announcing
the (possible) end of the world, while on the
back of this genuine public interest, a serious
programme of public understanding of science
4.26
– spanning the whole range of Spaceguardrelated topics – could be developed.
A recent example shows how difficult it is to
control the monster. Earlier this year, everyone
agreed that the asteroid 1999AN10 could not
possibly hit the Earth in 2027, despite the likelihood of an exceptionally close approach.
(Caveats, for example, included whether the
object might be a comet and could suddenly
start outgassing, or might hit an interplanetary
boulder that changed its path, or any number
of possible low-probability scenarios.) The
splash in the UK newspaper The Sunday People, however, reported: “At 7.42am on August
7, 2027 the world will come to an end ... that’s
if the boffins have got it wrong by 9 minutes!”
“People do not understand how
to respond to the aired
possibility of low-probability,
high-consequence events”
Scientists are caught – almost literally –
between a rock and a hard place. The
announcements have to be made, else they are
accused of censorship or – worse – a cover up,
leading to loss of trust in so-called experts. But
the issue is also potentially serious, involving
issues of national concern (which could diverge
for different nations), even the future of civilization. Such discussions should not occur
entirely in the rarefied atmosphere generated by
self-selected experts.
An impact hazard index?
One problem, succinctly expressed by David
Morrison (NASA Ames, and Chair of the IAU
Working Group on NEOs), is that “people just
don’t understand probability”. In particular,
people do not understand how to respond to
the aired possibility of low-probability, highconsequence events, and it was therefore suggested that the information should be presented in a simpler way.
One proposal, presented by Rick Binzel
(MIT), was to use an impact hazard index, in
which events occurring with a probability
comparable to the annual background rate for
a similar-size object would receive a hazard
index of 0 or 1, implying that they are “down
in the noise” and therefore not worth getting
concerned about. Higher impact probabilities
for the same size object would receive a higher
index, on a scale 2–10, with 10 denoting the
virtually certain impact of the canonical 10 km
diameter dinosaur-killer.
A possible difficulty with this approach is that
it demotes the background impact rate to a level
of insignificance, when in fact it is the significance of background impacts, in comparison
with other possible environmental disasters,
that makes the asteroid impact hazard unique.
A second possible difficulty is that in practice
most discussions are likely to revolve around
whether a particular object is a “one” or a
“two”, making largely redundant the precise
and detailed definition of an impact hazard
scale extending, for public consumption, over
the full range 0–10. Although there was general agreement that a way has to be found to
communicate results to the public in an accurate and effective way, it would appear that
Binzel’s proposed “Turin Impact Scale” is at
once too simple-minded and too complicated.
An alternative solution, namely better education of the general public in the finer points of
impact probabilities at the ~10–5 per annum
level (i.e. comparable to the annual probability
of the Earth being struck by a kilometre-sized
body with attendant global consequences
involving billions of deaths), has many attractions, not least its application to other spheres
of public policy. For example, even lowprobability events killing “only” a few hundred people at the ~10–5 per annum level, are
already assessed – and mitigated – by government agencies across a wide range of health
and environmental areas, because they are
deemed intolerable. At the other extreme, governments are occasionally forced into making
unplanned expenditure and policy shifts, simply because the public has failed to appreciate
that a much lower annual risk of disaster (e.g.
at the 10–9 level) is normally regarded as tolerable. Examples such as BSE or GM foods are
no doubt debatable, but a vigorous programme of public understanding of science in
this area could be beneficial.
Conclusions
The workshop was notable for the spirited,
sometimes heated debates on these issues, and
some memorable contributions from the floor.
The participants agreed several resolutions for
consideration by government departments and
funding agencies. In particular, given that a
vigorous start to the Spaceguard programme
has now been made by one nation, namely the
USA, contributions by other nations with relevant expertise, especially those in Europe or
with access to the southern sky, would be particularly welcome.
In fact, the meeting recognized that only in
this way will a genuine international programme be generated, allowing the full objectives of the Spaceguard survey, namely to identify and characterize any large asteroid or
comet due to impact the Earth within the next
century, to be achieved within the next 20
years. European astronomers have an important role to play. ●
Mark E Bailey, Armagh Observatory.
August 1999 Vol 40