CCNet, 27/2003 -  10 March 2003

"Europe's great comet-chasing mission is back on. The Rosetta probe,
which has been more than 10 years in development, will now head for
67P/Churyumov-Gerasimenko in February, 2004. The remarkable mission, which
has so far cost £600m, will pursue the comet at breakneck speed and
then attempt to put a lander on its surface."
--Jonathan Amos, BBC New Online, 7 March 2003

"The odds that a collision with a tiny meteor triggered the shuttle
Columbia catastrophe are one in 330, Canadian experts have calculated for
NASA. These findings, based on a unique Canadian radar installation,
are being incorporated into the investigation by the U.S. space agency
into what caused the break-up of the shuttle and loss of all seven crew
last month."
--The Toronto Star, 9 March 2003

    Russian Information Agency Novosti, 9 March 2003

    The Toronto Star, 9 March 2003

    BBC New Online, 7 March 2003

    Vishnu Reddy <>

    Alan Boyle's Cosmic Log, 7 March 2003

    Sandy Starr <>

    Jens Kieffer-Olsen <>

    The Scotsman, 10 March 2003


>From Russian Information Agency Novosti, 9 March 2003

IRKUTSK, March 9, 2003. /from RIA Novosti correspondent Alexander Batalin/ -
Irkutsk scientists are preparing for an expedition to the place of the fall
of a large meteorite in the taiga within the basin of the Vitim River,
Eastern Siberia.

Senior researcher with the solar and earth physics institute at the Siberian
branch of the Russian Academy of Sciences Sergei Yazev says that the
expedition will take place in March, before the start of the Siberian spring
(late April). It is important for scientists to gather the samples of small
dispersion (meteorite) powder expected to remain in the snow because it may
be washed away by melted snow water.

The scientists intend to employ a helicopter and snow tracked vehicles to
look for the exact place of the meteorite's fall within the boundaries of
the Botaibinsky and the Mansko-Chuisky districts of the Irkutsk region.

According to the scientist, the specialists estimate the weight of the Vitim
meteorite at 160 tons upon its entry into the atmosphere while only 60 tons
could reach the Earth. This exceeds the size of the Sikhote-Alin bolid
(large meteorite), one of the largest in the 20th century.

Another summer expedition will be needed to specify these data. Along with
Irkutsk scientists, specialists from Moscow will also participate in it.



>From The Toronto Star, 9 March 2003


LONDON, Ont.-The odds that a collision with a tiny meteor triggered the
shuttle Columbia catastrophe are one in 330, Canadian experts have
calculated for NASA.

These findings, based on a unique Canadian radar installation, are being
incorporated into the investigation by the U.S. space agency into what
caused the break-up of the shuttle and loss of all seven crew last month.

"The risk of Columbia being hit or critically damaged isn't much different
than other shuttle flights," said Peter Brown, an astronomy professor at the
University of Western Ontario, and world-recognized expert on meteors.

At NASA's request, Brown and colleagues at Western made the risk calculation
by using counts of the actual number of tiny meteors - called meteoroids -
that would have been in the path of Columbia during its 16-day orbit of

A $1 million special radar installation, operated by the university,
continuously tracks the path above Earth of thousands of meteoroids, some no
thicker than a human hair.

The Columbia was the first shuttle mission when the radar was in full
operation, scanning a 300-kilometre swatch above southern Ontario.

Brown said that a meteoroid no wider than a tenth of a millimetre could
cause serious damage to the shuttle because it would hit at as much as 50
times the speed of sound.

NASA is looking at meteoroid impact as a possible explanation for the
shattering of one of the ceramic heat tiles that protected the shuttle from
blowtorch heat as Columbia re-entered the Earth's atmosphere on Feb 1.

The loss of just one tile could produce a zipper effect, NASA engineers
feared, with superheated air blasting into the initial gap to pry loose a
string of tiles. The heat of re-entry would burn through the shuttle's thin
aluminum skin and attack fuel and hydraulic lines.

The Western meteor-tracking radar, paid for by NASA, is the only one of its
kind in the northern hemisphere. The only other similar station, in
Australia, surveys a narrower swath of sky.

Called the Canadian Meteor Orbit Radar (pronounced "see-more"), the
installation's spindly antennas stretch across four hectares at a pig farm
about 100 kilometres from this city in southwestern Ontario.

Brown said the preliminary calculation from the Canadian observations were
relayed to NASA officials last week.

The Western researchers are carrying out further analysis on the size, speed
and orbit of meteoroids that Columbia would have encountered.

"These things are moving faster than the shuttle so they can catch up with
it from behind. But there are more impacts from the front, on the shuttle's
leading edges, where the particles and the spacecraft are coming together at
20 to 30 kilometres a second. That's more than twice the speed of a bullet,"
said Brown.

Copyright 2003, The Toronto Star


>From BBC New Online, 7 March 2003

By Jonathan Amos
BBC News Online science staff 

Europe's great comet-chasing mission is back on. The Rosetta probe, which
has been more than 10 years in development, will now head for
67P/Churyumov-Gerasimenko in February, 2004.

The remarkable mission, which has so far cost £600m, will pursue the comet
at breakneck speed and then attempt to put a lander on its surface.

The first attempt to launch Rosetta in January this year - to Comet Wirtanen
- had to be called off when concerns were raised about the reliability of
its rocket.

Europe's Ariane 5 vehicle is currently grounded following the loss of a
launcher shortly after blast-off late last year.

Long mission

Scientists confess they know relatively little about Churyumov-Gerasimenko
and are therefore busy studying the object to learn more about its size,
shape and behaviour.

Barring any surprising discoveries, the choice of Churyumov-Gerasimenko will
be confirmed by the European Space Agency's Science Policy Committee in two
month's time.

If any adjustments need to be made to Rosetta, they will have to be minor.
There is not enough time between now and the launch window next year in
which to make radical changes to the probe.

"It's great to have a new target," Dr Chris Lee, an Imperial College London
researcher working on Rosetta, told BBC News Online.

"Because it is such a long mission, there was a fear that if we waited
several years before launching, people would start to drift away from the
project and the expertise would be lost."

Bigger pull

Just like its first mission plan, Rosetta will get to Churyumov-Gerasimenko
via a series of complex space manoeuvres.

These will go out to Mars and back, producing a slingshot that will build
Rosetta's speed up to the point where it can catch the comet out near
Jupiter and then follow the body in towards the Sun.

The timescales involved are similar, too, with the rendezvous possible in

The larger size of the comet - it is three or more kilometres in diameter -
compared with Wirtanen could pose some problems for the lander part of the

Researchers are concerned that Churyumov-Gerasimenko's gravitational
attraction will pull the lander in at a much higher velocity than the craft
was designed for.

The landing team are now looking at the possibility of redesigning its legs
to help cushion the impact.

Accident investigation

"There really is very little time to change anything on the mission," said
Dr Lee. "If you make changes, they have to be re-qualified; you have to do
mock-ups and testing."

The decision to postpone Rosetta had come as a bitter blow to the scientists
and engineers who had worked on the project for a decade or more.

The mission's problems began in December last year when Europe's new super
rocket, the Ariane 5-ESCA, exploded over the Atlantic on its maiden flight.

Although Rosetta was scheduled to fly on a standard version of the Ariane 5,
the post accident investigation ordered a thorough review of systems on all

The delay while this was carried out pushed Rosetta beyond the launch window
necessary to get it into position to catch Wirtanen.

Copyright 2003, BBC


>From Vishnu Reddy <>

Hi all,

Here is the summary of the activities by Spaceguard India during the first
two months of 2003. We hope you enjoy reading about our work and we welcome
you comments are suggestions.

clear skies
Vishnu Vardhan Reddy
Spaceguard India

Activities of Spaceguard India

Everyday our planet is bombarded by tonnes of meteors from outer space. At
times, some asteroids and comets, disturbed by gravitational pull of
planets, get pushed into odd orbits and pose a threat to the earth. These
asteroids and comets, collectively called as Near-Earth Objects, pose a
grave threat to mankind.

Already, many professionals and hundreds of amateur astronomers around the
world are actively participating in tracking these objects. It is
unfortunate that with a population of over a billion people, India has
remained in the background and has contributed little to
NEO research.

In an effort to popularise asteroid research in a small way among amateur
astronomers and the public, Spaceguard India was formed this year. As part
of this effort, Spaceguard India organised a series of workshops and
lectures for amateur astronomers and students in different parts of India
early this year. These workshops were held in collaboration with local
amateur astronomy clubs, planetaria and science colleges.

January 2003
Introductory Workshop on Asteroids-1
The first workshop in the series was held in the western city of Ahmedabad
in collaboration with the local astronomy group, 1 AU. The workshop was held
at Vann Chetana, a local forest department auditorium, on Saturday, 25th
January, 2003. Over 25 participants attended the half-a-day workshop. Apart
from amateur astronomers, researcher and students from the Physical Research
Laboratory also attended the workshop. The lectures were followed by an open
discussion session in which participants expressed their views on amateur
astronomy research in India.

An introductory session on CCD imaging was also organised after the workshop
and participants imaged some objects with the CCD camera till early next
morning. Apart from the workshop, an interactive session with astronomy
students at PRL was also organised. Participants were also given a CD-ROM
with sample CCD images and freeware for image processing and doing
astrometry. A soft copy of 60-page booklet about NEO research was also

Introductory Workshop on Asteroids-2
The second workshop was held in Thane, a satellite city of Mumbai, on
Wednesday, 29th January, 2003. The local organiser was the physics
department of B.N. Bandodkar College of Science. The workshop also saw the
formal launching of Spaceguard India. A press conference was held on that
occasion which was covered by leading national dailies and television

Nearly 40 participants attended the workshop, mostly students and amateur
astronomers. Apart from open discussion, a practical demonstration of
various of techniques used in asteroid hunting were shown to the
participants. A CD-ROM with the proceedings of the workshops was also given.

The practical CCD observation session was held at B.N. Bandodkar College of
Science on the 30th night. Apart from the workshop participants, more than
100 amateur astronomers and member of the public took part in the observing
session. A few engineering students showed keen interest in building a
cookbook CCD camera.

A public lecture on Near-Earth Asteroids was organised in collaboration with
Hope, Here on Project Environment, a non-governmental organisation, in
Thane. Over 100 people attended the talk, which was followed by a question
and answer session.

February 2003
Introductory Workshop on Asteroids-3
The last workshop in the series was held in the capital city of New Delhi on
Saturday, 8th February, 2003. The workshop was conducted in collaboration
with the Nehru Planetarium and the Amateur Astronomers' Association, Delhi.
Over 50 participants attended the half-a-day workshop. Apart from local
physics students and amateur astronomers, a few outstation participants also
attended the workshop. Each participant was given hands on experience in
doing asteroid astrometry using Astrometrica. Due to bad weather, CCD
session could not be held after the workshop.

Public Talk on Asteroid Impacts and night sky observation
A public night sky observation was organised by Spaceguard India at the
Indian Institute of Technology, Delhi on Friday, 21st February, 2003. The
observation was part of IIT's Tryst - its technical festival. More than 500
students attended the observation, which went on till early next morning. A
sunspot observation was also conducted next morning for students.
This was followed by a public talk on Asteroid Impacts at IIT, which was
attended by students and staff members.

Talk 1:Introduction to asteroids, comets and other minor bodies in the Solar
Talk 2: Scope for amateur research on asteroids: Visual observing,
Photography, Asteroid hunting, Asteroid astrometry, Asteroid photometry.

Talk 3: How to discover an asteroid?

Talk 4:Demonstration of various methods used in asteroid hunting including
blinking of CCD images and asteroid astrometry.


>From Alan Boyle's Cosmic Log, 7 March 2003

The moon has figured in war planning since ancient times, and it's no
different in the 21st century. The phases of the moon, as well as earthly
political realities, would point toward an assault in the latter part of
March, with the conditions becoming increasingly favorable as the calendar
nears April.

U.S. military planners would prefer to avoid the full moon on March 18 -
which just happens to be the day after the revised deadline for Iraqi

"It's certainly not optimum," said retired Rear Adm. Stephen Baker, who was
involved in enforcing the sanctions against Iraq in the 1990s and is now a
senior fellow at the Washington-based Center for Defense Information. "On a
clear full-moon night in the environment of Iraq, you could possibly
visually acquire aircraft."

In addition to giving Iraqi aircraft-spotters an advantage, a cloudless,
moonlit night would actually be a handicap for U.S. soldiers equipped with
night-vision equipment, Baker said.

"If you think about it, with night-vision goggles, a full moon is almost too
bright," he said. "Everyone's got night-vision goggles nowadays. With the
third-generation night-vision goggles that we all have, they're light
enhancers, so we don't need the moon.

"We certainly prefer owning the night and having Iraq blind, if you will,"
Baker said.

Rather than fighting against the moon's glare, the U.S. military would want
to maximize its advantage over Iraqi defenders on a dark night. After March
18, the waning moon would rise progressively later and later, leading up to
the new moon on April 1. Even commodity traders have figured out the "new
moon" war factor - and it could well play a role in financial markets as the
month wears on.

The phase of the moon won't be the prime factor behind war planning, of
course; but if the Battle of Baghdad is to begin in the next month,
astronomy would argue for later rather than sooner.

"If there's a choice of one or two or three days, predicated on other
factors like the weather ... it's a planning and an operational factor, but
it's not a show-stopper," Baker said.

There have been some occasions in military history when a full moon, rather
than a new moon, was preferable for an attacking force. For example, the
Japanese started launching planes for their 1941 Pearl Harbor attack during
the full moon so that their carrier pilots could see more clearly.

The Allies' invasion of Normandy in 1944 was even more finely tuned, so that
a late-rising moon would provide cover for the approach of airborne troops
but light the way once they reached their targets. Three days in early June
were thought to satisfy those conditions and have propitious tides as well.
Eisenhower went with the middle of the three days, June 6, even though the
weather was a bit iffy.

Weather could play a role this time as well: For example, if there's a high
overcast in Iraqi skies, that would cancel out much of the concern about the
lighting conditions at night, Baker said. But even the weather may not be as
critical a factor as it has been in earlier conflicts.

In the past, cloudy weather has posed problems for determining the effects
of air strikes - the so-called bomb damage assessments, or BDAs. But Baker
doesn't expect that to be so much of a problem for Gulf War II, in part
because of all the advances in aerial drone capability.

"With our infrared capability, and the fact that we're going to have
Predators and Global Hawk as well as all the sensors and satellites that we
have, I don't know if it's going to be all that much of a degradation," he

Since Gulf War I, the U.S. military has also come a long way in the use of
"smart weapons" such as JDAM bombs, which are guided to their targets by
Global Positioning System readings. If they work as advertised, which is
sometimes a point of debate, that also would minimize concerns about adverse

Our "Building Toward War" interactive provides additional perspective on
today's weapon systems, and you can also check out the "Virtual Soldier" at
the military Web site for Fort Lewis in Washington state.

Copyright 2003, MSNBC


>From Sandy Starr <>

Thursday 6 March 2003

Why are we so obsessed with risk, and what are the consequences of this
obsession? From global warming to mobile phones, from crime to child safety,
from the business world to the military, precaution and pre-emption have
become the buzzwords of our time.

On FRIDAY 9 MAY 2003, a London conference entitled 'PANIC ATTACK:
INTERROGATING OUR OBSESSION WITH RISK', produced by the online publication
spiked ( in association with the online publication
bring together an international audience to assess the spread of risk
aversion into ever-more spheres of life.

Speakers include:

- MICK HUME (editor, spiked; columnist, The Times)
- GEOFF MULGAN (UK government Performance and Innovation Unit)
- PROFESSOR CARL DJERASSI (father of the modern contraceptive Pill)
- PROFESSOR FRANK FUREDI (author, 'Culture of Fear')
- PROFESSOR BJØRN LOMBORG (author, 'The Skeptical Environmentalist')
- PROFESSOR SIR COLIN BERRY (experimental pathologist)
- JIM GLASSMAN (host, Tech Central Station)
- DR MICHAEL FITZPATRICK (health columnist, spiked; author, 'The Tyranny of
- DR PETER MARSH (director, Social Issues Research Centre)
- SALLIE BALINUAS (enviro-sci host, Tech Central Station)
- JEYA HENRY (professor of human nutrition, Oxford Brookes University)


Friday 9 May 2003, at:

The Royal Institution
21 Albemarle Street
London W1S 4BS

Speaker, session and booking details for the conference are available online

For further details, contact:
SANDY STARR at spiked
Tel: +44 (0) 20 7269 9234
Fax: +44 (0) 20 7269 9235



>From Jens Kieffer-Olsen <>

Dear Benny Peiser,

On Monday, March 03, 2003 you wrote:

> By contemplating what may happen in the event of a small
> impact, we need to recognize the psychological and social
> implications of traumatic events and the emotional and
> irrational reactions they can activate. The social effects
> of an impact are all too often ignored or underestimated,
> but they could be extremely grave. Such effects perhaps
> could be even more disruptive than the physical damage
> and economic costs.

I believe you are doing a particularly sterling job by emphasizing the
social effect of NEO impacts. Articles on CCNet have touched on various
aspects of this consequence, but so far none has attempted a summing up.
That of course is because the major fallout is either material, policial, or
economical depending on the area hit and the severity of casualties.  In any
case, the material side of a disaster is often the only one being addressed
outside of CCNet.

Peisergrams don't easily lend themselves to tabular presentations due to
most fonts being proportional, but let me outline a skeleton approach:

 A.  Tunguska-size objects ( ~100m ) striking
       1.  Thinly populated areas
             a.  Material impact limited
             b.  Political impact a 'memento mori'
             c.  Economical impact restricted to insurance companies
       2.   Populated areas
             a.  Material impact similar to 9/11
             b.  Policial impact similar to 9/11
             c.  Economical impact may require Marshall-aid to mend
       3.   Metropolitan areas
             a.  Material impact similar to war-time carpet bombing
             b.  Political impact could tilt regional power balance
             c.  Economical impact could be a world-wide depression

The key points above are 1.b, 2.c, and 3.a
B.  Country-size killers ( ~300m ) striking
        1.  Thinly populated areas
              a.  Material impact vast ecological disaster
              b.  Policial impact a rush toward a credible Space Guard
              c.  Economical impact serious for countries affected         2.   Populated areas
              a.  Material impact annihilation of entire provinces
              b.  Policial impact affected by pseudo-religious 'explanations'
              c.  Economical impact will put international solidarity to the test
        3.   Metropolitan areas
              a.  Material impact similar to effect of nuclear attack
              b.  Political impact an international take-over if small country hit
              c.  Economical impact world-wide chaos

The key points here seem to be 1.b, 2.a and 3.c

C.    Global killers ( ~1km ) striking any area
               a.  Material impact may be more serious farther away
               b.  Policial impact world-wide chaos
               c.  Economical impact indistinguishable from war
The key point here is of course C.b

To sum up I conclude that the fallout from a small impact will be political
and on a positive note, if it happens in a remote area, otherwise the
aftermath will be licking human and material wounds.

As the size of the impactor increases, the economical consequences will
prevail with indirect casualties a result of chaos, but at the same time
political and/or religious 'fundamentalism' could change the course of

Global events almost certainly will spell a 'new world order', either
through a direct US take-over, or - if destruction has focused on North
America - by the emergence of some other
superpower. - No wonder that American concerns center on large asteroids!

Yours sincerely
Jens Kieffer-Olsen, M.Sc.(Elec.Eng.)
Slagelse, Denmark


>From The Scotsman, 10 March 2003

"THE moment of maximum human danger always sees the best jokes. This from
America: news comes that Paris is about to be hit by a giant asteroid in 12
hours. The US emergency services phone the White House to ask what should be
done. The president goes into conference. It's a tough call - should he
watch the event live on CNN, or tape it to watch at his leisure?..."

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>From AstroBiology Magazine, 10 March 2003

Summary: In this encore to the Great Impact Debate series, the debate
participants respond to questions posed by our readers. Such questions
include: "Are nuclear detonations, such as those depicted in the movie
'Armageddon', the best way to divert asteroids?" and "Can a passing asteroid
dramatically increase the Earth's temperature?"


Clark Chapman - scientist at the Southwest Research Institute's Department
of Space Studies, in Boulder, Colorado. Member of the MSI/NIS
(imaging/spectrometer) team of the Near Earth Asteroid Rendezvous (NEAR)
mission to Eros. 

Alan Harris - senior research scientist at the Space Science Institute, an
affiliate of the University of Colorado at Boulder.
Benny Peiser - social anthropologist at Liverpool John Moores University in
the UK. He has written extensively about the influence of NEO impacts on
human and societal evolution.
Don Yeomans - (debate moderator) - Senior Research Scientist at NASA's Jet
Propulsion Laboratory in Pasadena, California, and manager of NASA's
Near-Earth Object Program Office. 

I remember hearing about an asteroid that passed close to Earth, but we
didn't even know it was there until it had already passed us. How could an
asteroid just appear out of nowhere like that if we're always scanning the
sky for them?

Don Yeomans: I believe you are referring to asteroid 2002 EM7, an object
that passed 1.2 lunar distances of Earth on March 8, 2002, but was not
discovered until four days later.

In this particular case, this rather small, 50-meter sized object passed
Earth coming from the direction of the sun, so it was in the daylight sky,
and hence unobservable with ground-based telescopes.

Objects of this size pass unnoticed within a lunar distance of Earth every
few months. Many are not discovered because they are small and faint.
Current survey telescopes often cannot pick them up until they approach the
Earth, so the time window for discovery is relatively short.

The asteroid 2002 EM7 was discovered when it became observable in the
nighttime sky. While close to the Earth, such objects have a distinctive
apparent motion against the stellar background, and it is this motion that
allows their discovery by wide-field survey telescopes. Once discovered,
these objects are normally observed for a long time - long enough that an
accurate orbit can be determined and predictions can be made about their
future motions in space. Then we can determine if such objects will come
close to Earth again.

Alan Harris: Such asteroids pass near the Earth many times before they
impact. The objective of the Spaceguard Survey is to discover asteroids as
they pass by the Earth on one of those prior occasions, which is exactly
what happened with 2002 EM7. Whether the asteroid was discovered while
approaching or receding is not a major issue.

In movies like "Armageddon" and "Deep Impact," nuclear detonations are used
to try to divert near-Earth objects. But I've heard this really is not a
good option, because it would break the asteroid into many pieces and
increase our odds of being hit. What is your opinion?

Clark Chapman: The advantage of using nuclear weapons to destroy asteroids
is that they are our most powerful devices by far. But the disadvantages are
many. In particular, the more we learn about asteroids and comets, the more
we realize that they are incredibly fragile. Most asteroids larger than a
few hundred meters across are now thought to be "rubble piles" --
collections of rocks, boulders, and "mountains" simply resting against each
other, loosely held together by the tenuous gravitational field of the

Any sudden force applied to such an object would likely tear it apart into a
swarm of objects. The total impacting energy of the swarm would be the same
as the original asteroid, but spread out across the Earth's surface. In any
case, once you disrupt a comet or asteroid into many different chunks,
you've lost all ability to affect what happens next. In short, it is a very
bad idea.

How would a comet impact differ from an asteroid impact? Or would there not
be much difference among objects of the same size and velocity?

Alan Harris: The main difference applies to objects just barely big enough
to penetrate the Earth's atmosphere, like the Tunguska event. We can
conclude the Tunguska cosmic body was a "hard stone" asteroidal object,
because if it had been soft and fluffy it would have exploded at a much
higher altitude than it did. Likewise, an iron body would have hit the
ground and produced a crater about the size of Meteor Crater in Arizona.

But for larger objects, the nature of the impactor hardly matters. A 1
kilometer-diameter object will punch right through the atmosphere regardless
of its velocity or composition. So if it is that large, there is not much
difference in effect between iron, rock, or a snowball of the same mass.

Suggested strategies to divert asteroids include an electromagnetic machine
that hurls dirt from the surface, an orbiting parabolic mirror to heat up
the surface and create a plume of vaporized material, or the low-tech
strategy to 'paint-it-black,' where the asteroid is coated so solar heating
would divert the asteroid. (Or alternatively, to strip a thin layer from the
surface -- the newly exposed colors would change the asteroid's thermal
properties enough to move it.) What do you think of these options, and what
would be your favored mitigation strategy if we only had three to five years
of advance warning?

Clark Chapman: The three approaches suggested in the question are
potentially viable. I see problems with the practicality of the
electromagnetic "mass driver" concept, but it is possible that a scheme
could be developed with more research. Three to five years warning is rather
short, though, so there would be little time to develop any technologies
that don't already exist.

I am very dubious about the "paint it black" concept, especially in the
context of a short warning time. The so-called Yarkovsky Effect, in which a
spinning body is slowly accelerated due to asymmetric re-radiation of
sunlight impinging on the body, is very weak and probably would be effective
only over a much longer duration. And having just gone through a terrible
saga last year getting my house painted, I'm skeptical about the
practicality of "painting" or "stripping" the surface of an asteroid!

The best technique might depend upon the size and nature of the threatening
body. I like the concept being explored by the B612 Project: attach a
low-thrust rocket (a long-acting, nuclear-powered plasma engine) to the
asteroid, de-spin it, and then move it away from its Earth-impact
trajectory. But further development and integration of the engineering
concepts are needed.

Could we reduce the danger from planet-killer sized asteroids by locating
all the troublesome objects and mining them out of existence? We would get
valuable materials and also save the planet.

Alan Harris: There are two problems with this concept. First, "all the
troublesome objects" at present is zero, and is likely to remain so. We
don't expect to find any asteroids on a collision course with the Earth. If
we did find one, "mining it out of existence" would be a vastly greater
enterprise than simply deflecting it off of a collision course.

There is a common misconception of the utility of space resources. With
present technology, it makes no sense to go into space for resources to
bring back to Earth. The only sensible utility of mining asteroids is for
resources to be used in space -- that is, to reduce the amount of mass that
must be thrown up into space against the Earth's gravity. We might
contemplate mining the offending asteroid to gain fuel to deflect it, or for
mass to run a mass driver, but not to bring stuff back home.

How many times in recorded history has a significant asteroid or comet
impact occurred? You mentioned the event in China where 10,000 people may
have been killed by asteroids. Is that the most deadly asteroid event that
has occurred for humans?

Benny Peiser: We have no idea how many significant impacts have occurred
during the last 10,000 years. While we have a number of historical records
that appear to refer to cosmic impacts, many of these accounts are too
ambiguous to give us any reliable information. This predicament is also true
for the various reports regarding the alleged impact disaster in China
during the 15th century.

Clark Chapman: A paper was published about half-a-dozen years ago that
interpreted ancient Chinese records in terms of meteoroid impacts. I found
essentially all of the instances in that paper to be *in*credible. A case of
stones raining down on an army violated one of the most characteristic
aspects of meteoroid falls: all the stones were interpreted to have been
about the same size. Instead, real debris from outer space -- whether broken
up in outer space or in an atmospheric explosion -- forms a "power-law size
distribution." There are a few big objects, and increasing numbers of small
objects at ever-smaller sizes.

Eyewitness reports in modern society are notoriously unreliable, and reports
from different cultures in ages long past are even more so. Presumably these
historical accounts refer to something, but I doubt that most (or any) of
them have much to do with impacts.

Benny Peiser: Unless you can verify the existence of an unambiguously dated
impact crater, historical records and eyewitness accounts are regarded as
insufficient evidence for an impact. We even find it difficult to believe
the descriptions of experienced astronomers, such Leon Stuart, who claimed
to have observed -- and indeed photographed -- a lunar impact in 1953.

This is a real dilemma since only around 5 percent of terrestrial impacts
produce a hypervelocity impact crater. For every crater-producing
multi-megaton impact, we can expect about 10 atmospheric or oceanic impacts
that fail to produce a "smoking gun." In other words, the vast majority of
small asteroids striking the Earth explode in the atmosphere. In rare cases,
as happened in Tunguska, atmospheric impacts can cause considerable
destruction on the Earth's surface without leaving any compelling
fingerprints (like an impact crater).

It is striking, nevertheless, that significantly more terrestrial impact
craters exist that date to the Holocene (the last 10,000 years) than we have
historical impact reports for. It seems the vast majority of historical
impacts went unnoticed. Another possibility is that impact reports were
censored by religious authorities who were concerned about the demoralizing
implications of these "divine interventions."

I read a story about an asteroid that is expected to pass close to Earth
sometime around the year 2016, and the temperature of the Earth would be
raised to 50 degrees Celsius (122 F) at the moment it passes by. Is that

Alan Harris: No. The topic of cosmic impacts brings out a lot of crackpot
claims, and this appears to be one of them. Even an asteroid "the size of
Texas" (as breathlessly declared in the movie "Armageddon") would have no
discernable effect passing close to the Earth -- as long as it didn't hit.

A proposal recently submitted to the European Space Agency has a fleet of
five mini-probes targeting an asteroid considered potentially dangerous.
Once in space, the probes would use ion propulsion engines that provide
thrust by shooting out a stream of electrically charged particles. How well
do you think this would work?

Don Yeomans: The European Space Agency has received several recent proposals
to utilize spacecraft to either discover near-Earth objects or study their
compositions and structures. None of these proposals would actually try to
use the very low thrust of ion propulsion engines to attempt an asteroid
deflection. One of these proposals, called SIMONE, would use five low-cost
spacecraft to fly by, or rendezvous with, a number of near-Earth objects to
gain an understanding of their physical nature. This information would be
invaluable should we one day have to deflect an Earth-threatening object.

The method employed in a future asteroid deflection attempt would depend
upon a detailed knowledge of the composition, mass, rotation, and structure
of the threatening near-Earth object. Although probably not appropriate for
deflecting a near-Earth object, low-thrust, ion-drive spacecraft are very
efficient in terms of propulsion. They are also very reliable. The Deep
Space 1 ion-drive spacecraft has been operating successfully in space since
October of 1998.

Could you describe what the public reaction to the 1908 Tunguska impact was
like at the time? Do you think the public today would respond differently?

Benny Peiser: The atmospheric impact over the Tunguska region in Siberia was
witnessed by many thousands of people and felt over an area of more than
1,000 miles in radius. Many native Tungus hunters were fairly close to
ground zero, and some of them witnessed the large-scale slaughter of their
deer herds as a result of the blast. Apparently, one or two hunters were
killed by the explosion. Reminiscent of religious leaders who blame natural
disasters on a vengeful deity, Tungus shamans told their people that
disobedience had brought divine calamity upon themselves.

Further away from the epicenter, the disaster also was witnessed with
trepidation. Just days after the impact, many Russian newspapers reported
the huge explosion. A newspaper from Irkutsk, for example, described how
peasants in the village of Nizhne-Karelinsk (200 miles from ground zero)
"saw a body shining very brightly with a bluish white light. When the
shining body approached the ground it seemed to be pulverized, and in its
place a huge cloud of black smoke was formed and a loud crash -- not like
thunder, but as if from the fall of large stones or from gunfire -- was
heard. All the buildings shook and at the same time, a forked tongue of
flame broke through the cloud. Everyone thought that the end of the world
was approaching."

Despite many similar reports and eyewitness accounts, newspapers and
scientists discarded the whole incident, claiming that such bizarre stories
were unsound and unreliable. As a result of this general disbelief, it took
some 20 years before the first scientific excursion reached ground zero to
investigate the causes of the catastrophe.

And what about today? It is unlikely that we will encounter another Tunguska
event in the near future. Impacts in the 10-megaton range probably happen
only once every 500 to 1,000 years. But for argument's sake, let us
contemplate how the public might respond if another Tunguska-type impact
happened tomorrow.

For a start, the reaction of the public fundamentally will depend on the
location, extent, and destruction of the impact. In all likelihood, another
Tunguska event would occur over an unpopulated or scarcely inhabited region
of the world. However, in the unlikely event of fatalities, the global
uproar could be substantial. In such a case, 9/11 would look like an
insignificant security failure. The blame game would be brutal, and I would
certainly not like to be in the shoes of those who had advised the
government that small impacts were negligible.

CCCMENU CCC for 2002