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CCNet 55/2003 - 10 July 2003
----------------------------


"Massive tsunamis, miles of raging forest fires, a stratosphere clogged
with enough debris to obscure the sun -- even a relatively small
asteroid striking Earth would wreak enough havoc to end civilization.
"It's not whether it's going to happen," said Bruce Weaver, director of
Monterey Institute for Research in Astronomy (MIRA). "The question is
how long it will be (until one hits)." Fortunately, the answer is likely
to be in the million-year range."
    --Kaija-Leena Romero, The Californian, 2 July 2003


"We cannot rely on statistics alone to protect us from catastrophe; such a strategy is like refusing to buy fire insurance because blazes are infrequent. Our country simply cannot afford to wait for the first modern occurrence of a devastating NEO impact before taking steps to adequately address this threat."
    --"Open Letter to Congress on Near Earth Objects"



(1) CONCERNED CITIZENS ASK FOR CONGRESSIONAL ACTION ON NEAR EARTH OBJECTS

(2) SPACE OBJECTS A THREAT

(3) OUR IRRATIONAL FEAR

(4) IMPACT HAZARD SUMMARY BY ANDREA MILANI

(5) SIBERIAN (BODIABO) BOLIDE OF 24 SEP 2002: CONTRADICTORY INFORMATION

(6) DOUBTS GROWING ABOUT RUSSIAN REPORTS ON 2002 ATMOSPHERIC IMPACT IN SIBERIA

(7) SPACE SOLAR POWER: THE FUTURE ENERGY RESOURCE?

(8) MISLEADING NATURE HEADLINE ("GALACTIC DUST COOLING EARTH?")


================
(1) CONCERNED CITIZENS ASK FOR CONGRESSIONAL ACTION ON NEAR EARTH OBJECTS

Space.com, 9 July 2003
http://space.com/scienceastronomy/neo_letter_030709.html

Concerned Citizens Ask for Congressional Action on Near Earth Objects
By Leonard David

A distinguished group of Americans joined together to send a unique request to Congressional leaders Wednesday -- a request that preparations be made to deal with the prospect of Earth being slammed by an asteroid or comet.

In an "Open Letter to Congress on Near Earth Objects," the communication underscores the danger our planet faces from near Earth objects, also termed NEO's.

The letter has been sent to President Bush and his cabinet, the Secretary General of the United Nations and to leaders around the globe.

Included among those that urged action on the NEO issue were: Apollo 17 Astronaut, Harrison Schmitt; Neil Tyson, Director of the Hayden Planetarium; Freeman Dyson, Professor Emeritus of Princeton University; Lucy Ann McFadden, NEO scientist at the University of Maryland; New York University professor and author, William Burrows; John Lewis, a scientist at the University of Arizona, Tucson; and Thomas Jones, former astronaut and veteran of four shuttle missions. 

Potentially devastating threat

"We write to you today as concerned citizens, convinced that the time has come for our nation to address comprehensively the impact threat from asteroids and comets," the letter begins.

The overall aim of the Open Letter is start a process to educate national leadership about the real threat posed by worrisome comets and asteroids that can approach Earth:

"A growing body of scientific evidence shows that some of these celestial bodies, also known as Near Earth Objects (NEOs), pose a potentially devastating threat of collision with Earth, capable of causing widespread destruction and loss of life. The largest such impacts can not only threaten the survival of our nation, but even that of civilization itself."

Three step effort

The letter urges U.S. lawmakers to take a series of three steps, thereby shaping a coordinated program to deal with the impact threat:

Step 1: NEO Detection - Expand and enhance this nation's capability to detect and to determine the orbits and physical characteristics of NEOs.

Step 2: NEO Exploration - Expand robotic exploration of asteroids and Earth-approaching comets and direct that U.S. astronauts again leave low-Earth orbit ... this time to further explore certain NEOs in deep space for information required to develop an effective capability to deflect an NEO should we learn that one threatens life on Earth.

Step 3: NEO Contingency Planning - Initiate comprehensive contingency planning for deflecting any NEO found to pose a potential threat to Earth. In parallel, plan to meet the disaster relief needs created by an impending or actual NEO impact. U.S. government/private sector planning should invite international cooperation in addressing the problems of NEO detection, potential hazards and actual impacts. This step also advocates establishment of an Interagency NEO Task Force to address the NEO Impact Threat. This Task Force should be composed of senior representatives from appropriate government agencies.

Insurance policy

Resources committed to the NEO work have been very modest, an enclosure to the Open Letter declares, "and not commensurate with the potential threat." What is warranted is additional investment in search programs, deemed by the letter's supporters as both "appropriate and prudent."

A dramatic improvement in the rate at which asteroids and comets are discovered would likely result if the United States were to increase the current level of funding, now at about $3.5 million per year, to at least $20 million annually, the letter's enclosure explains.

The Open Letter concludes: "For the first time in human history, we have the potential to protect ourselves from a catastrophe of truly cosmic proportions."

"We cannot rely on statistics alone to protect us from catastrophe; such a strategy is like refusing to buy fire insurance because blazes are infrequent. Our country simply cannot afford to wait for the first modern occurrence of a devastating NEO impact before taking steps to adequately address this threat."

Prudent approach

A leader in scripting the NEO Open letter is former shuttle astronaut, Thomas Jones. He is a veteran space traveler of shuttle missions, STS-59, 68, 80, and 98.

Contacted by SPACE.com, Jones said he is hopeful that the Open Letter stirs Congress to take action. But he is also realistic.

"It may very well take an impact to shake things up and make the government act," Jones said. "But since it's a basic responsibility of government to provide for the common defense, and since that mission is spread over many agencies, we thought that Congress is the right body to address the hazard, and to direct a joint approach."

If Congress takes no action, Jones said that he and the other supporters hope the President will act in response.

"It seems no one agency desires to take the lead on this, but since many have roles to play, from Homeland Security to Defense to NASA, our hope is that Congress can direct a concerted plan of action," Jones told SPACE.com.

"We already devote taxpayer funds to disaster preparedness in advance of other natural hazards, and so we call for a similar, prudent approach to studying and countering the impact hazard," Jones concluded.

To read the Open Letter in its entirety: www.CongressNEOaction.org

Copyright 2003, Space.com

================
(2) SPACE OBJECTS A THREAT

The Californian, 2 July 2003
http://www.californianonline.com/news/stories/20030702/localnews/580059.html

By Kaija-Leena Romero

Massive tsunamis, miles of raging forest fires, a stratosphere clogged
with enough debris to obscure the sun -- even a relatively small
asteroid striking Earth would wreak enough havoc to end civilization.

"It's not whether it's going to happen," said Bruce Weaver, director of
Monterey Institute for Research in Astronomy (MIRA). "The question is
how long it will be (until one hits)."

Fortunately, the answer is likely to be in the million-year range. With
a grant from NASA, however, MIRA hopes to find out more about objects
hurtling through space that are potentially dangerous to Earth.

Most of the asteroids roaming outer space have been swept into various
orbits over the past 5 billion years or so, Weaver said, but there are
still thousands out there that move into our own galaxy.

Fortunately, most asteroids in our solar system orbit between Mars and
Jupiter. Those that come within the orbit of the Earth or which
planetary movements could bring into the Earth's orbit are considered
"near-Earth objects."

Research on asteroids close to the Earth used to be almost impossible.
The small, fairly dark chunks of rock or nickel moving at 10 to 20 times
the speed of a bullet didn't lend themselves to observation.

If the scientist observing an asteroid didn't determine its orbit almost
immediately, the size of the asteroid could not be determined.

Often, as in the case of an asteroid passing between Earth and the moon
a few years ago, the observations were in retrospect. Scientists didn't
realize that the asteroid would pass so close to Earth until after it
happened.

Scientist Russell Walker, however, when working with images from an Air
Force infrared-seeking satellite, found that pictures of the Milky Way
would often accidentally include images of asteroids that allowed
astronomers to indirectly determine their size.

When compared with previous observations about their orbits, researchers
had a much better idea of which asteroids were the most dangerous to
Earth.

The grant from NASA will allow MIRA to continue its work reviewing the
infrared images, and much farther down the line, when many more
asteroids are cataloged, Weaver said, possibly even divert asteroids
from a collision course with the Earth. The grant is particularly
important to MIRA as the Institute is not funded by a university or a
single source. It runs on a combination of grants, gifts, and occasional
contracts, such as the NASA grant. Founded 30 years ago in Monterey,
MIRA now has both a main office in Marina and a research observatory on
Chews Ridge in Los Padres National Forest.

Copyright ©2003 The Californian
 
=================
(3) OUR IRRATIONAL FEAR

Psychology Today, 3 July 2003
http://www.psychologytoday.com/htdocs/prod/PTOArticle/PTO-20030703-000002.asp

By Richard Lovett

Summary: Why we worry too much about man-made catastrophe. The answer
may lie in how our brains are wired, allowing us to respond to danger
before we've even had time to think about it.

Each year Earth is pelted by space debris, from tiny grains to car-sized
boulders, their impact equivalent to a kiloton of TNT. Every 1,000 years
or so, a bigger rock smacks our planet with the force of a hydrogen
bomb.

So why aren't we quaking in our boots? David Ropeik, director of risk
communication at the Harvard Center for Risk Analysis, believes it's
because asteroids are natural; we're far more terrified of man-made
risks such as terrorism or bioengineered foods. Also, we've never
watched an asteroid impact on TV, so we don't really believe it could
happen.

Ropeik is intrigued by why people are disproportionately afraid of some
things but can ignore others. The answer may lie in how our brains are
wired, allowing us to respond to danger before we've even had time to
think about it. At the 2003 meeting of the American Association for the
Advancement of Science, he noted that if our ancestors hadn't been
designed this way, they wouldn't have survived.

Experience and culture also teach us what to fear. We're born with some
basic phobias, but we must learn that DDT and terrorists are dangerous.
Ropeik says we're more afraid of catastrophic events such as airplane
crashes than of everyday risks like cancer. It's partly a matter of
media coverage that makes the danger appear greater than it is; and
partly because the more grisly the prospect, the more it frightens us.
The result is a certain degree of illogical behavior.

From a statistical perspective, says Clark Chapman, Ph.D., an asteroid
researcher at the Southwest Research Institute, in San Antonio, Texas,
it was "very strange" that the deaths of a few people from anthrax
dominated the news in late 2001, while the risks of influenza, which
killed 30,000, "were just buried." That distortion, adds Geoff Sommer, a
graduate student at the think tank Rand Corporation, is the essence of
terrorism. It works as a "weapon of mass distraction," siphoning
attention from other arenas.

As for those not-so-scary asteroids: one did hit Siberia in 1908,
leveling hundreds of square miles of forest. The National Aeronautics
and Space Administration is now mapping the orbits of 2,000 large rocks
likely to hit our planet in the future.
 
Copyright 2003, Psychology Today

================
(4) IMPACT HAZARD SUMMARY BY ANDREA MILANI

Science, 20 June 2003

Asteroid and comet impacts on the Earth did happen many times in the
past. Raise your eyes to the Moon: what you see is a surface
saturated by craters.  The largest lunar impacts, however, happened
before 3,800 million years ago. Over a time scale comparable to human
life the largest impact was at Tunguska, Siberia, in 1908, by an
asteroid <70 meters in diameter. A recent reassessment of the
Tunguska-class impacts suggests that the average frequency for
impacts of this size is only one in about 1,000 years (1).

The rate of impacts is a function of the impactor size. Large
impacts, forming craters tens of kilometers in diameter, are very
rare events over the time scale of human life and civilization,
frequent events over geological times. The most energetic impacts
could have triggered some of the transitions between geological eras.
65 million years ago an impact by a ~10 kilometer diameter asteroid
generated a ~100 million Megaton explosion and excavated the 180
kilometer wide Chicxulub crater in Mexico. Its ash layer covers the
entire surface of the Earth and marks the transition between the
Cretaceous and the Tertiary eras, across which most dinosaurs became extinct.
The mechanisms of the extinctions are not established, but the
association with the crater cannot be a coincidence.

For a given impact energy the physical effects can be modeled with
the methods developed for nuclear weapons. These effects are local:
the Tunguska impact flattened a few thousands square kilometers of
desert taiga. The loss of life due to a Tunguska-class impact is
unlikely to exceed that of other natural disasters (2).  For a much
larger impact the most damaging effects could be the global ones. An
explosion of thousands of Megatons could change atmospheric chemistry
and world climate, could damage the biosphere and affect mankind
through global failure of food crops. This chain of consequences is
hard to model in a quantitative, predictive way.

What, then, is the frequency of impacts that could kill one billion
people, or even result in extinction of the human species? The
uncertainties exceed one order of magnitude. A Chicxulub-class
impact, expected only once in 100 million years, may result in
extinction of mankind. An impact of ~1,000 Megatons, expected to
occur every ~60,000 years (3), should not have global effects,
although the local effects might include Tsunami waves affecting an
entire ocean basin. Somewhere in between, at few kilometers in
diameter and at once every few million years, lies the frequency of
the unknown critical sized impactors for global effects.

The Spaceguard goal

The cause of the impact risk is the population of Earth-crossing
asteroids and comets. Most asteroids orbit around the Sun between
Mars and Jupiter, while most comets have orbits beyond Neptune. As a
result of planetary, stellar, or non gravitational perturbations, a
small fraction of both classes ends up in unstable orbits and close
approaches to our planet become possible.  To compile a catalog of
all these Near Earth Objects (NEO) is the first goal; to scan the
entire sky became possible with the development of CCD cameras and of
the necessary software (4). This made feasible the so called
"Spaceguard goal": to discover 90% of all the NEO with diameter 1
kilometer or larger.

The choice of targeting the surveys to objects above 1 km is optimal,
provided that this coincides with the critical size for global
effects. This can be shown by a probabilistic computation of the
expected damage, in human lives lost per year (5). The onset of
global effects is believed to increase the number of casualties by as
much as an order of magnitude. If this is true, then the expected
casualty rate is approximately the number of casualties just above
the global effect threshold times the frequency of such an impact
(6). Thus, if the casualties are 1 billion and this happens once in a
million years, the expected damage is ~1,000 deaths per year (7).
The contribution of the more frequent Tunguska-class impacts is
minor: the expected damage is a few tens of thousands casualties
divided 1,000 years, or a few tens per year.  Thus to target for
discovery the objects just above the global effects threshold is the
most "cost effective" way to decrease the risk.

This "insurance approach" to the problem of impact risk appears
questionable to many, including myself. Two other rational arguments
can be used. We could agree on a level of damage we consider
unacceptable: an impact by a 1 km asteroid, with energy comparable to
a global thermonuclear war, could be considered unacceptable even if
it might not trigger global effects.  The other argument is the
technological limit: there is no point in setting a goal we cannot
achieve in the foreseeable future. At the beginning of the 90's both
arguments supported the Spaceguard goal, that could be achieved in
few decades, by using telescopes of limited size (8). In conclusion,
there was no mathematical theorem proving that the Spaceguard goal
was optimal, but it was a reasonable approximation.  Being a simply
stated and achievable goal, it has contributed significantly in
spreading the discussion outside of the scientific community.

In 1998 NASA, upon request from the US Congress, accepted the task of
achieving the Spaceguard goal in 10 years.  With support from NASA
(also from scientific institutions and the US military) there has
been a very encouraging progress in the NEO searches. From 1998
essentially all the observable sky became covered to a depth
corresponding to apparent magnitude 18.5. As a result, the number of
NEO discovered has grown very rapidly: now (9) we know 569 Near Earth
Asteroids (NEA) with absolute magnitude brighter than 17.65,
corresponding to 1 km diameter for average albedo (10). The number of
NEA with 1 km diameter and larger is now estimated at about 1000,
with a comparatively small uncertainty (3). Thus NASA has been able
to claim that the Spaceguard goal is now more than half achieved, but
the number of NEA of a given size remaining to be discovered
decreases exponentially. The current survey simulations predict that
a significant upgrade in the survey telescopes is required to achieve
the goal by 2008; this upgrade is taking place.

The Spaceguard goal does not completely account for the risk of
impacts by comets. Short periodic comets can be detected with the
same techniques used for NEA, but a long periodic comet can have a
close approach to our planet only a few months after becoming
observable. The probability of an impact by a single long periodic
comet is very small (~1/1,000,000,000 per perihelion passage). To
assess the risk of impacts with a given energy by long periodic
comets we would need to have much more information on the mass of
these objects. A very rough estimate indicates that the risk from
long periodic comets is at least one order of magnitude less than
that from NEA, for the same impact energy range. Still, this implies
that it may not be possible to go much beyond the 90% Spaceguard goal
for risk reduction without taking into account long periodic comets.

Is observation enough?

Can we assume that, as soon as a NEO is observed, its contribution to
the total impact risk becomes zero? To detect the asteroid/comet
signal in a CCD frame is not enough to discover a NEO. A number of
observations are needed to compute an orbit: e.g., Apollo was
detected in 1930, but discovered, with a computed NEO orbit, only in
1932.  Main belt asteroids are detected by the hundreds for each NEO
detection, but the current survey systems aiming to discover NEO
cannot follow up all the detections. Unfortunately, it is not always
easy to discriminate a NEO from the main belt detections. An object
moving at a fast angular rate must be a NEO, a slower moving one is
most likely main belt.  But a fraction of NEO are detected while
moving at main belt rates. Thus the requirement of following up only
the NEO is inconsistent.

The progress in NEO discovery has been slowed down by the failure to
appreciate that all the asteroid/comet data are also data on NEO. The
only way to be sure that a given detection is not a NEO is to
identify it with a main belt asteroid with a known orbit. Because the
asteroid identification problem is a mathematically difficult one
(11), all the detection data, from all surveys, should be available
for competitive research of asteroid identifications. In the past
this did not happen, also because of obsolete "discovery credit
rules" discouraging publication of data until a full discovery could
be announced.  There are now encouraging indications that the
observers have understood that to extract as much information as
possible from the raw data is in the best interest of the scientific
community.

Virtual and real impactors

Even after a NEO has been observed long enough to compute an orbit,
its future position belongs to an "uncertainty region" that grows
with time. At some time in the future such region could touch the
Earth. Is it possible to establish whether a NEO, with a given set of
observations, can or cannot impact the Earth in the next, say, 100
years?  This issue was raised forcefully in March 1998, when an
ambiguously worded statement about the NEA 1997 XF11 issued by the
Minor Planet Center resulted in a media storm.  Scientists in this
field have learned that making a public announcement on a possible
impact is a difficult task. But the main issue was not a PR problem.
As of 1998 nobody knew how to solve the mathematical problem of
detecting possible future impacts.

Although the orbit of an asteroid is perfectly deterministic, we need
to describe its future position in a probabilistic way, to quantify
our ignorance of where the object really is. We can describe this as
a swarm of virtual asteroids (VA): only one of them is the real one,
but we do not know which one.  If one of the VA has a very close
approach to the Earth at some time in the future, in such a way that
a minute modification of the orbit, still compatible with the
observations, results in an impact, then there is a Virtual Impactor
(VI). Each VI is associated with a non-zero probability of impact. If
we only want to detect the VI with large probability, then only a few
VA orbits must be computed. If the risk is one of a catastrophic
impact we are interested in knowing about minute probabilities
(1/1,000,000 and less). In this case a brute force approach would
require to compute millions of VA orbits, and this task is beyond the
current generation of computers (12). This problem can be overcome if
a set of VA are assembled into a geometric object, such as a string.
With this approach (13), VI for the asteroid 1999 AN10 could be
detected at a probability level of one in a billion, using only ~1000
VA.

Since 1999, the impact monitoring robot CLOMON at the University of
Pisa has used this approach to monitor each newly discovered
asteroid, scanning the possible evolution of the orbit for the next
80 years to look for VI to probability levels 1/1,000,000 and below.
In 2002 the second generation monitoring system Sentry (14) went on
line at Jet Propulsion Lab, California, and CLOMON2 replaced the
first robot in Pisa (15). By comparing the output of the two systems,
we have reached very high levels of reliability.

If no VI are found, the asteroid is safe. If VI are found, the two
robots send alarm messages to the human operators. The observers,
coordinated by the Spaceguard Central Node (SCN) (16), then keep
track of the object until new observations, decreasing our ignorance
of the future orbit, force the probability of the impact down to
negligible values. This procedure has now been used dozens of times,
and all VIs, including those of the 2 km-diameter 2002 NT7, have been
eliminated by observation within a day to several months.

Beyond Spaceguard

In an increasingly connected world, the sudden death of many people
is considered less acceptable, thus actions to prevent it should meet
with increasing support. As new technology for CCD chips and arrays,
faster computers and telescopes in the 4-m to 6-m class become
available, a more ambitious goal than Spaceguard should be formulated.

A post-Spaceguard goal could be to discover 90% of the NEO down to
300 meters in diameter and to increase the completeness for those
with diameter >1 km to, say, 97%, with provisions for a better
understanding of the risk due to long periodic comets. Such a goal,
to be achieved within the next 10 to 20 years, is realistic. The
issue is who should provide the resources for achieving it.

It might be argued that the discovery of NEO is not pure scientific
research, but rather a civil defense task. As such, it could be
responsibility of other agencies, both civil and military, different
from the ones funding science. In the USA, the US Space Command has
expressed interest, whereas NASA does not seem keen to take
responsibility beyond the Spaceguard goal.  Other countries have
funded theoretical research (such as the one done in Italy), some
interesting initiatives such as the Bisei center in Japan, and some
public relations exercises (such as the one going on in the UK); but
overall, support for NEO searches has been negligible. If this does
not change the international community, in particular the scientific
one, might not play a major role in handling the NEO impact risk.

The more an issue is critical for the safety of mankind, the less it
should be entrusted to a bureaucratic and secretive organization.
Would you like to know that maybe an asteroid is on collision course
toward the Earth, but some organization is taking care of it without
public discussion? Our experience with the asteroid observational
data confirms that the involvement of military organizations implies
enormous difficulties in implementing the open data policy that, as
outlined above, is necessary. On the contrary, the scientists are
committed to publish the results of their research, because
scientific knowledge remaining secret has no long term value and
generates no credit.  The NEO impact risk assessment should therefore
remain the responsibility of the international scientific community
(17).

If the basic technology required is available, such a task is within
the level of effort and resources normally available for scientific
research.  However, NEO searches are seen by many astronomers as less
fundamental than other scientific goals, such as elucidating the
origin and large scale structure of the universe. This way of
thinking neglects two important points. First, the relevance of a
scientific discovery for humankind depends also on its practical
implications: knowledge about what could destroy us should have some
priority. Science should pursue knowledge for the sake of knowledge,
but this does not imply that knowledge without practical application
is "more fundamental" (17).

Second, no planetary system can form without comets and asteroids.
There is indirect observational evidence that such small bodies
exist, for example as the steady state source of the transient dust
belts around many stars. Spectroscopic data have shown that comets
and asteroids impact the star Beta Pictoris (18) in the same way as
our Sun (19). Small bodies thus exist around other stars and have
similar dynamical behavior. Their collisions with each other and with
planets are a universal phenomenon, and should be included in all
astrophysical and exobiological models of the evolution of
extra-solar planetary systems.

In my opinion, the scientific community should take upon itself the
duty to investigate the NEO population at the level of knowledge
necessary to identify all possible impactors, down to the size
compatible with available technology and with the public perception
of acceptable risk. In the next decades, this should go well beyond
the Spaceguard goal, with the help of sky surveys by large telescopes
such as LSST and Pan-STARRS (17).

Worst-case scenario

Observations and computations to date have not discovered a likely
impactor. It is unlikely that a serious threat is discovered in our
lifetime (20). But what should be done if such an impactor is
identified? We cannot justify the effort to discover it unless we can
safeguard of our planet even in this worst case.

The effort necessary to deflect an asteroid to avoid a collision goes
well beyond the level of resources available to the scientific
community and cannot be prepared before the need arises.  On the
contrary, the know how necessary for such a task should be gathered
in advance. The space agencies, such as NASA and ESA, have the
necessary capabilities and are interested in including this goal in
their mission.

This year NASA has convened a workshop to identify the scientific and
technological knowledge which would be necessary for an asteroid
deflection (21). One such requirement is to understand the internal
structure of an asteroid, otherwise an attempt at deflection may
result in disruption, with loss of control on the pieces. The
European Space Agency (ESA) has funded several studies of innovative
NEO missions. One of them, called Don Quijote, would involve two
spacecrafts. The Hidalgo probe should impact a small asteroid (~500
meter in diameter) at a relative velocity >10 km/s, while the Sancho
spacecraft orbits the same asteroid. This allows to study the
internal structure of the asteroid by seismology and to test a
non-nuclear deflection technique, by measuring the amount of
deflection achieved. If this mission is found to be technically and
economically feasible, the knowledge necessary to face the worst case
will become available. (22)

Notes & References

(1) Harris, A. Bull. Amer. Astron. Soc. 34, 020 (2002)

(2) Even now the average density of the human population on the
surface of the Earth is only ~12 per square kilometer. Tunguska-class
impacts on major cities are less likely than impacts by significantly
larger bodies.

(3) Morbidelli et al., Icarus, 158, 329 (2002)

(4) Carusi, A. et al., in Hazards due to comets and asteroids,
T. Gehrels et al. eds, (Univ Arizona press, Tucson, 1994), pp 127-148.

(5) It is obtained formally by an integral of the product of the
yearly probability for an asteroid of a given size times the estimated
casualties from such an impact.

(6) Morrison, D. et al., in Hazards due to comets and asteroids,
T. Gehrels et al. eds., (Univ. Arizona Press, Tucson, 1994) pp. 59-92;
Chapman, C.R. and Morrison, D., Nature, 367, 33 (1994).

(7) The size distribution of the NEO is steep, with objects 10 times
larger a few hundred times less numerous, thus Chicxulub-class
impacts, being much rarer, contribute little to the total risk.

(8) Not more than 2 meters in diameter; such telescopes have limited use
for competitive research in other fields of astronomy and are
available.

(9) NEODYS, January 2003; available at http://newton.dm.unipi.it/neodys/

(10) Chesley, S.R. et al., Icarus, 159, 423 (2002).

(11) Milani,A., Icarus, 137, 269, (1999).

(12) Milani, A. et al., in Asteroids III, R. Binzel et
al. eds. (Univ. Arizona Press, Tucson, 2003).

(13) Milani,A. et al, Astron. Astrphys., 346, L65. (1999).

(14) Sentry http://neo.jpl.nasa.gov/risk/

(15) The output of CLOMON2 is included in the same web site as NEODyS,
see (3).

(16) SCN http://spaceguard.ias.rm.cnr.it/spaceguard/

(17) While in the rest of the paper I am summarizing the scientific
consensus, in these paragraphs I am  expressing a very personal
opinion.

(18) Beust, H., et al.,  Astron. Astrophys. 310, 181, (1996).

(19) Farinella, P. et al., Nature, 371, 314 (1994).

(20) E.g., there is a probability of 1 in 630 that a 1000 megaton
impact will occur in the next 100 years.

(21) NASA Mitigation Workshop, extended abstracts volume:
http://www.noao.edu/meetings/mitigation/eav.html

(22) The author has been assisted, in preparing this article, by Nanni
Riccobono (Tumbling Stone) and Julia Fahrenkamp-Uppenbrink (Science).

=============================
(5) SIBERIAN (BODIABO) BOLIDE OF 24 SEP 2002: CONTRADICTORY INFORMATION

David Morrison <david.morrison@nasa.gov>

by David Morrison with news clips assembled by Benny Peiser for CCNet

On September 24 of last year a very bright fireball or bolide was
witnessed over the same general part of Siberia that was hit by the
Tunguska asteroidal projectile in 1908. Many who saw it reported that
it hit the ground, but this is a common fallacy associated with most
eyewitness account of fireballs. About a month later the US
Department of Defense released the following information: "US
satellites detected the impact of a bolide near Bodiabo in Siberia at
16:48:56 UTC on 24 September 2002. The object was simultaneously
detected by both visible wavelength and IR sensors. The object was
first detected at 57.91 North Latitude, 112.90 East Longitude at an
altitude of approximately 62 km.  It was tracked to 58.21 N, 113.46 E
at an altitude of approximately 30 km. The observed visible
wavelength peak intensity  was 2.4 X 10^11 Watts/ster. The total
radiated energy was 8.6 X 10^11 Joules (6000K black body)."

For comparison, this radiant energy release is about the same as that
of the Tagish Lake bolide in the Yukon on 18 January 2000, and is
about a factor of 5 larger than that of the Park Forest (Chicago)
bolide of 27 March 2003. Peter Brown estimates the total yield of
both Bodiabo and Tagish Lake at about 2 kilotons -- a factor of
roughly 10,000 less than Tunguska, which released an energy of
approximately 15 megatons. Note that both Tagish Lake and Park Forest
yielded many small meteorites. Finding these meteorites was greatly
helped by the circumstances of the target: Tagish Lake stones fell on
snow, and Park Forest stones fell in a populated region where many
hit roofs or fell on paved streets and parking lots.

It was surprising, therefore, to read the following three stories in
June

METEORITE CRASH SITE FOUND IN SIBERIA
IRKUTSK. June 6 (Interfax) - The crash site of a gigantic meteorite,
Vitim, that hit Earth in September has been discovered in the Irkutsk
region. An expedition from the Kosmopoisk scientific organization
found an area of about 100 square kilometers covered with burnt trees
and pieces of the meteorite 60 kilometers from the village of Mama. .
. . The expedition members said that this is the second largest
meteorite, after the famous Tunguska meteorite, to fall on Russian
territory.

LARGE METEORITE FRAGMENTS FOUND IN SIBERIA
MOSCOW, JUNE 6 (RIA NOVOSTI CORRESPONDENT EDUARD PUZYREV) -
Prospectors from the Kosmopoisk expedition have spotted a
100,000-square-kilometer part of the taiga with burnt and fallen
trees. It is found 60 kilometers from the Mama village near the Vitim
river, said the academy. When the meteorite was falling, people in
many places near the Bodaibo and Mama villages felt earth tremors as
in an earthquake. They also "heard roar and splashes of light above
the taiga forest far away."

METEORITE CRASH SITE LOCATED IN SIBERIA
MOSCOW (AP) -- Researchers from the Kosmopoisk, or Space Search,
research group told Rossiya state television Thursday that they
believe a burned-out tract of taiga about 1,100 kilometers (700
miles) north of the city of Irkutsk is the spot where one or more
meteorites fell on September 25. Vadim Chernobrov, Kosmopoisk's
coordinator, said the meteorite crash was "comparable to the force of
a medium atomic bomb." Chernobrov said that after examining the site,
the research team believes two meteorites actually fell, not just
one, as previously thought.

----------------------------------------------------------

How should these stories be interpreted? With skepticism, I believe.
A meteoritic explosion of 2 kilotons energy taking place at an
altitude of 30 km is unlikely to have generated a serious shock wave
or induced seismic signals. It is extremely unlikely to have started
a forest fire; it is a good rule of thumb that meteorites land cool
and don't start fires. Finding meteorite fragments in a forested
wilderness would also be fortuitous, to say the least. One can only
wonder what was really found and to what degree the news reports
reflect actual information collected by Russian scientists.

+++++++++++++++++++++++++++++++++++++++++++

NEO News is an informal compilation of news and opinion dealing with
Near Earth Objects (NEOs) and their impacts. These opinions are the
responsibility of the individual authors and do not represent the
positions of NASA, the International Astronomical Union, or any other
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dmorrison@arc.nasa.gov. For additional information, please see the
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please include this disclaimer.

============
(6) DOUBTS GROWING ABOUT RUSSIAN REPORTS ON 2002 ATMOSPHERIC IMPACT IN SIBERIA

From: Benny Peiser
Sent: 03 July 2003 09:48
To: 'Stuart Goldman'
Subject: RE: CCNet: SIBERIAN IMPACT FLATTENS 40 SQ MILES OF FOREST

Dear Stuart

I'm afraid I haven't got any new information on the Bodaybo event. I
did find out, however, that Vadim Chernobrov, who is the main spokesperson
of the reported expedition to the impact site is an UFO enthusiast. This
makes his account of the alleged expedition to the site a bit more
suspicious:
http://www.virtuallystrange.net/ufo/updates/1998/oct/m16-018.shtml

Nevertheless, there have been earlier reports of people who claimed to
have seen the physical effects of the atmospheric impact. On 4 October
2002, Interfax reported:

"Polyakov said there were more than 100 eyewitnesses and that
scientists trusted them. He said instruments rarely recorded meteorite
falls and so eyewitnesses were practically the only source of information
on such events for scientists. He cited hunters as saying the supposed
meteorite had left a large crater surrounded by burned forest."
http://www.interfax.ru/show_one_news.html?lang=EN&tz=0&tz_format=MSK&id_news=5598245

I guess the best way to find out is to get in touch with the Russian
research scientists who actually visitied the site.

Hope this is helpful.

Best regards
Benny

-----Original Message-----
From: Stuart Goldman [mailto:sgoldman@SkyandTelescope.com]
Sent: 02 July 2003 19:47
To: B.J.Peiser@livjm.ac.uk
Subject: Re: CCNet: SIBERIAN IMPACT FLATTENS 40 SQ MILES OF FOREST


(1) METEORITE CRASH SITE FOUND IN SIBERIA

Dear Dr. Peiser,

I've been trying to track down information about the September Bodaybo
bolide and several weeks ago I had communicated with Peter Brown and
Mikhail Nazarov about what they knew about the event. Their conclusions
were that, yes, there was a bolide, but the data (and lack thereof)
suggested that it wasn't terribly destructive. Instead of Tunguska, it
was more akin to the meteorite-scattering bolide over Chicago in March.
However, the Russian TV report adds more fuel to the fire by suggesting
that there's a vast area of scorched forest and felled trees. This might
be supportive of a larger blast, if the trees reveal flash burns on one
side, fell in a radial direction, etc. In my mind, it's still in
the "maybe" category.

Have you received any additional detail about this event since your
last CCNet posting on June 19th? The article I've written is now at the
printer, but we have a little less than a day that we can alter it if
there's something significant to note.

Thank you very much.

Sincerely,
Stuart Goldman

+-------------------------------------------------+
   Stuart Goldman      sgoldman@SkyandTelescope.com
   Associate Editor    http://SkyandTelescope.com/
   Sky & Telescope
   49 Bay State Rd.      Phone - 617-864-7360 x141
   Cambridge, MA 02138     Fax - 617-576-0336
   USA

==============
(7) SPACE SOLAR POWER: THE FUTURE ENERGY RESOURCE?

SciScoop, 7 July 2003
http://www.sciscoop.com/story/2003/7/7/22911/60842

At this year's International Space Development Conference, Saturday, May
24, was the main day for the Moon track, which I had coordinated
(representing the Moon Society). The morning sessions covered use of
lunar resources for space solar power systems, with the morning plenary
talk given by David Criswell of the University of Houston. Criswell's
proposal has been around in one form or another for about 20 years now,
but received significant publicity last year after the California energy
crisis and his publication of a summary of the proposal in the April/May
2002 issue of The Industrial Physicist. Criswell also contributed to an
article published in Science magazine last November, which concluded
that the only reasonable options to provide power to the Earth through
the next century are fusion and space-based solar power.
 
The starting point for Criswell's argument is world energy needs, here
on Earth - unless most of the world is to stay "dirt poor", we're going
to need something like 20 TW electric by the middle of this century;
2000 TW-yrs of electric energy per century for the foreseeable future.
Where can this possibly come from?

Criswell discussed the various currently viable alternative energy
options, none of which comes close even with massive environmental
damage. And then there's the lunar solar power plan. Through utilization
of space resources, the power plots would grow almost exponentially - a
first demo would deposit production machinery to produce solar power
plots from lunar materials; second phase would deposit manufacturing
equipment on the moon to produce 90% of the production machinery needed
from lunar materials.

All this seems to be feasible now, based on research dollars already
spent: $1 billion on the lunar material returned by Apollo, $50 million
spent on space solar power studies, $2 million spent on utilization of
lunar material for space solar power purposes; the main assumptions are
a reasonable reduction in launch costs ($500 - $1000/kg) and that we can
actually achieve 90% bootstrapping and tele-operation for most of the
work.

With these assumptions Criswell showed some cost estimates that came to
a total of $7 trillion for the 20 TW system; this included delivery of
about 63,000 tons of material to the lunar surface, and a gradual
buildup of the lunar infrastructure. About 400 people would be needed on
the Moon, another 60 in lunar and Earth orbit, to support the system.
For power sold at 1 cent per kWh, by my calculations that's about $1.75
trillion/year revenue; Criswell quoted $80 trillion, but I believe that
was the total for the first century of operation, including ramp-up.

There are additional uses for the lunar solar power system: power beams
can be used to deflect asteroids and comets, and they can power space
missions well beyond the Moon-Earth distance. Cis-lunar resources will
provide around $3 Trillion/year revenue in lunar and space industries,
he estimated.

Current spending on Earth for oil and gas exploration is about $130
Billion/year -- shouldn't large private energy companies be interested?
But the scale of this project seems to be too large an investment for
business - if it's to happen, the US government has to step up and fund
it. If the support was there, work on the lunar solar power system could
be started with about 8 years to the first facilities on moon, and
electrical power returned to Earth about 12 years from the start.

Following Criswell's talk we had a panel discussion on development of
space solar power. Seth Potter of Boeing focused on large-scale space
construction techniques, which will be needed soon for construction of
large space telescopes and facilities planned for the Earth-Moon L1 and
Earth-Sun L2 locations. I then spoke on options for powering the first
lunar base - minimizing mass while providing continuous power through
the lunar night-span suggests a constellation of solar power satellites
for a near-side base up to about GW power levels, and then an L1 power
satellite for higher power. John Strickland then talked about the
transition points in developing solar power satellites, based on launch
cost from Earth - at $2 million/tonne ($1000/lb - transition pt 1)
Earth-launched SPS's are competitive with terrestrial solar; at
$200,000/tonne ($100/lb - transition pt 2) they become competitive with
fossil fuels. Use of lunar resources can move transition point 2 to 1 or
earlier. Strickland then talked a bit about the difficulties of getting
the various players who should be involved, on board. Why can't
environmentalists, for example, be a major source of support?

The panel then convened and took questions from one another, and from
the audience. David Criswell playfully suggested that the only way to
get NASA and industry serious about real innovations in space transport
and resource utilization was to start by moving NASA HQ and oil company
CEO's to the Moon! There are many players who could have an interest -
the manufacturing automation that space industry will require should be
of general interest; power consumers should care; investors and mutual
funds, environmentally friendly places with energy problems like the
state of California, or the European Union, etc. But US government
involvement seems really needed as primary risk taker.

From the audience there was a comment that the lunar solar power scheme
was "too grandiose", which led to its lack of support. What is really
needed are smaller steps; smaller infrastructure development, near-Earth
capability; small steps are more palatable. There followed a general
discussion of the balance between incrementalism and large focused
development (Criswell contrasted the "large focused development" of
Apollo with the incrementalism of post-Apollo NASA). That was one issue
we ended up having two sides agreeing to disagree about!

After hearing the talks and discussing further with some of the
attendees, I came away even more impressed with the huge solar power
resource we have just sitting out there in the space between Earth and
Moon; vastly more energy than we could ever hope to get from fossil or
fission fuels. And with about as low an environmental impact as you
could possibly hope for. But I also came away somewhat depressed at the
way this whole area has been ignored since the 1970's.

A 1979 DOE/NASA "reference" study of solar power satellites concluded
that, while feasible, a minimum $250 billion investment was needed
before the first power could be returned to Earth. Funding dried up
almost completely after that. A "Fresh Look" study in the 1990's showed
that alternate designs could bring the cost to first power down under
$10 billion; neither study assumed any use of lunar resources, but given
an existing lunar industrial base (building the base might well go over
that $10 billion), use of lunar materials can bring down the costs per
GW delivered even further. The "Fresh look" prompted a bit more funding,
but a National Academy review noted that the funding levels were far
from sufficient to meet the R&D needs identified; since then, far from
getting more money to do what's needed, the program within NASA seems to
have been cut for FY 2002 and 2003. Unfortunately, as John Strickland
indicated, a lot of these projects are viewed as impractical until we
can get launch costs much lower than they now are, but there's a bit of
a catch-22 there, since the primary reason launch costs are still so
high is the very limited market for launch... At least the space
elevator would suddenly make all this very practical.
 
==============LETTERS==============

(8) MISLEADING NATURE HEADLINE ("GALACTIC DUST COOLING EARTH?")

Duncan Steel <D.I.Steel@salford.ac.uk>

Dear Benny,

I was excited by the NATURE story headline:

>(1) GALACTIC DUST COOLING EARTH?

because I imagined this had something to do with dust-loading of
the atmosphere reflecting away sunlight (as Bill Napier postulated
for comet-derived dust in a paper in the Monthly Notices of the RAS
last year). I am also an author of the paper that first identified
an influx of interstellar (i.e. galactic) dust to the atmosphere:
A.D. Taylor, W.J. Baggaley & D.I. Steel, 'Discovery of interstellar dust
entering the Earth's atmosphere,' Nature, 380, 323-325 (1996).

However, the first words of the report:

>The impact of cosmic rays on our climate might outweigh that of the
greenhouse gas carbon dioxide, a controversial new report suggests1.

makes it clear that no dust is involved here. Cosmic rays are not
'dust'. They are high-energy elementary particles (e.g. protons,
electrons) and single atomic nuclei, plus gamma rays (i.e. photons),
but not large aggregates such as could be termed 'dust'.

Regards,

Duncan Steel

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