PLEASE NOTE:

• Information circulated on the cambridge-conference network is for
  scholarly use only. The attached text may not be reproduced
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*

CCNet, 26/2003 -  7 March 2003
------------------------------

"For the past few weeks, impact aficionados have been abuzz over the
apparent confirmation that a house-size object struck the Moon on November
15, 1953. The bright flare captured that evening by Leon H. Stuart's
backyard telescope matches the position of a small, fresh- looking
crater recorded by a spacecraft three decades later. But a little more
historical digging would have shown that there was no mystery to begin
with. John E. Westfall has discovered that the bright blip seen by
Clementine also appears in a series of telescopic plates taken decades
before Stuart snapped his controversial exposure."
--J. Kelly Beatty, Sky & Telescope, 5 March 2003


(1) LUNAR FLASH DOESN'T PAN OUT
    Sky & Telescope, 5 March 2003

(2) MEANWHILE AT THE NYT: "NEW EVIDENCE SUPPORTS MOON BLAST"
    The New York Times, 4 March 2003

(3) SIMULATIONS OF COLLISIONS SHED LIGHT ON INTERNAL STRUCTURE OF ASTEROIDS
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(4) NEW MOONS FOR JUPITER
    BBC News Online, 6 March 2003

(5) NEWTON WAS NOT A PROPHET OF DOOM
    The Daily Telegraph, 4 March 2003

(6) FIREBALL OVER CENTRAL CANADA
    CNews, 5 March 2003

(7) HANDLE WITH CARE: METEORITES STRIKE YATINUWARA AND WENNAPPUWA
    Sunday Observer (Cylon ), 2 March 2003

(8) MEETING ON ASTEROIDS AND COMETS IN EUROPE
    Stephen Laurie <stephen@laurieco.com>

(9) TECHNIQUES FOR ESTIMATING THE RISK OF SMALL AND MEDIUM IMPACTS: HOW
ACCURATE ARE THEY?
    E.P. Grondine <epgrondine@hotmail.com>

(10) AND FINALLY: THE END MIGHT BE NIGH IN 20 BILLION YEARS
     Space.com, 6 March 2003


=============
(1) LUNAR FLASH DOESN'T PAN OUT

>From Sky & Telescope, 5 March 2003
http://skyandtelescope.com/news/current/article_890_1.asp>

By J. Kelly Beatty

March 5, 2003 | For the past few weeks, impact aficionados have been abuzz
over the apparent confirmation that a house-size object struck the Moon on
November 15, 1953. The bright flare captured that evening by Leon H.
Stuart's backyard telescope matches the position of a small, fresh-looking
crater recorded by a spacecraft three decades later. Bonnie J. Buratti (Jet
Propulsion Laboratory) and Lane Johnson, a student at Pomona College,
unearthed this 1½-kilometer-wide "smoking gun" in data from the Clementine
orbiter, whose high-definition cameras mapped the entire Moon in 1994.

Although the annals of amateur astronomy chronicle hundreds of such
transient lunar phenomena, almost all considered suspect by professionals,
Stuart's event stands apart because it was both seen and photographed. That
fact, together with the Clementine evidence, allowed Buratti and Johnson to
make a convincing case in January's issue of the scientific journal Icarus.
A press release even trumpeted "NASA Solves Half-Century Old Moon Mystery."

But a little more historical digging would have shown that there was no
mystery to begin with. John E. Westfall (Association of Lunar and Planetary
Observers) has discovered that the bright blip seen by Clementine also
appears in a series of telescopic plates taken decades before Stuart snapped
his controversial exposure. In particular, Westfall notes, the feature is
"pretty obvious" in photographs made with Mount Wilson's 100-inch Hooker
telescope in 1919. It also turned up on plates taken in 1937 with the
36-inch refractor at Lick Observatory and in others acquired with Catalina
Observatory's 61-inch reflector in 1966.

"It's kind of disappointing," Buratti said when told of Westfall's
revelation. "But it's more important to find that out." In researching their
paper, she and Johnson had examined a few telescopic images for a small
crater at the impact's presumed coordinates but found nothing. A search of
Lunar Orbiter frames, taken during the 1960s, also turned up empty. They
concluded that the candidate crater must be too small (roughly 0.8 arcsecond
across) to be resolved by ground-based efforts.

Even before Westfall came forward, doubts had been growing about the
Stuart-Clementine connection. For one thing, Stuart reported that the bright
flare lasted at least 8 seconds, an implausibly long fireball for so small a
crater. "We now know that an event of that scale should last no longer than
a second, but [Stuart] didn't," comments impact specialist Alan W. Harris
(Space Science Institute).

A respected radiologist in Tulsa, Oklahoma, Leon H. Stuart enjoyed observing
with his home-built 8-inch f/8 Newtonian telescope. At its upper end is the
plate camera used to record his controversial lunar flare on the evening of
November 15, 1953. Courtesy Jerry Stuart.
 
Other concerns were raised about the freshness of Buratti and Johnson's
candidate crater. Solar-wind bombardment causes lunar material to darken and
redden over time, but researchers believe such "space weathering" takes
place slowly over millions of years. Thus, if 20-meter-wide objects slam
into the Moon frequently (often enough to make Stuart's sighting
statistically plausible), then the lunar landscape should be peppered with
100,000 bright, fresh-looking splashes - and it isn't. "You can't have it
both ways," notes Harris.

Finally, the positional match wasn't as good as Buratti and Johnson first
thought. Careful measurement of Stuart's image by Sky & Telescope editors
Dennis di Cicco and Gary Seronik, as well as by Westfall, shows that the
flare is centered a full 1°, or 30 km, from the Clementine candidate.

So, if it wasn't a flashy impact, what did Leon Stuart see and photograph a
half century ago? Some have suggested that it was a "point meteor," headed
directly at the camera, but that is ruled out by the flare's duration.
Moreover, the spot on the photographic plate is perfectly round, arguing
against a stray reflection or emulsion defect. In 1967 Stuart's original
underwent a battery of tests at the University of Arizona's Lunar and
Planetary Laboratory. But today the whereabouts of the original plate are
unknown, and without it the true mystery of "Stuart's event" may never be
solved.

Copyright 2003 Sky Publishing Corp.

=============
(2) MEANWHILE AT THE NYT: "NEW EVIDENCE SUPPORTS MOON BLAST"

>From The New York Times, 4 March 2003
http://www.nytimes.com/2003/03/04/science/space/04MOON.html

By HENRY FOUNTAIN

Humans have gazed at the Moon in wonder since ancient times, but what Dr.
Leon Stuart observed one night in 1953 was more wonderful than what anyone
had seen before or since.

Looking through his eight-inch telescope at his home near Tulsa, Okla., Dr.
Stuart, a radiologist by profession but an astronomer by avocation, saw and
photographed a bright flash on the Moon's surface.

Dr. Stuart was certain that he had witnessed a small asteroid hitting the
Moon, the flash being the fireball from the event. An amateur astronomy
journal published his photograph and report, and it has remained a curiosity
over the years. While some scientists thought his explanation plausible,
others were convinced that he saw an optical aberration or a much closer
object, like a meteorite in Earth's atmosphere (or, embarrassingly, an
airplane passing overhead).

Now new research shows that Dr. Stuart's flash on the Moon was no flash in
the pan. An astronomer at NASA's Jet Propulsion Laboratory, poring over
high-resolution lunar photographs, has found a fresh crater in the precise
area where Dr. Stuart saw his flash....

===============
(3) SIMULATIONS OF COLLISIONS SHED LIGHT ON INTERNAL STRUCTURE OF ASTEROIDS

>From Andrew Yee <ayee@nova.astro.utoronto.ca>

Centre National de la Recherche Scientifique
Paris, France

Researcher contact:
Patrick Michel
Observatoire de la Côte d'Azur
e-mail: michel@obs-nice.fr
Tel: +33 4 92 00 30 55

Contact INSU:
Philippe Chauvin
e-mail: philippe.chauvin@cnrs-dir.fr
Tel: +33 1 44 96 43 36

Press contact:
Martine Hasler
Tel: +33 1 44 96 46 35
e-mail: martine.hasler@cnrs-dir.fr

February 6, 2003

Simulations of collisions shed light on the internal structure of asteroids

An international team of researchers led by Patrick Michel (Observatoire de
la Côte d'Azur - CNRS, Nice) have carried out simulations of asteroid
collisions. For the first time, such simulations have made it possible to
provide information about the internal structure of asteroids and, in
particular, have shown that the parent bodies from which asteroid families
have originated must have been fragmented (and non-monolithic) bodies or
stacked rocks. The formation of an asteroid family results from the break-up
of such a body, which creates hundreds of thousands of fragments, certain of
which could become dangerous asteroids and meteorites. These findings also
show that the impact energy during a collision is highly dependent upon the
internal structure of the target; this information is very useful for the
development of a strategy of defense against the threat of an impact with
the Earth. The researchers' results are published in the February 6, 2003,
issue of Nature and are featured on the journal's cover.

In the asteroid belt, which is located between Mars and Jupiter, asteroid
families are concentrated groups of small bodies that share the same
spectral properties. More than 20 families have been identified, each family
believed to be fragments resulting from the break-up
of a large parent body in a regime where gravity, more than the material
strength of the rock, is the key factor (*). The actual size and velocity
distributions of the family members provide the main constraint for testing
our understanding of the break-up process in this gravitational context. A
new asteroid family, which bears the name of its largest member, Karin, was
recently identified and studied. It is the youngest family discovered to
date, and appears to have resulted from a collision around 5 million years
ago. This family provides a unique opportunity to study a collisional
outcome that is relatively unaffected by phenomena such as collisional
erosion and the dynamic diffusion of fragments, which, over time, alter the
properties resulting directly from the collision.

Patrick Michel of the Cassini Laboratory (Observatoire de la Côte d'Azur -
CNRS) and two of his colleagues from the Universities of Bern (Switzerland)
and Maryland (USA), have developed numerical simulations of collisions with
the aim of determining the classes of events that make it possible to
reproduce the main characteristics of the Karin family. As the results
depend to a large degree on the internal structure of the parent body, they
were able to show that this family must have resulted from the break-up of a
body that was originally full of fracture and/or empty zones, rather than a
purely monolithic body. Their findings moreover indicate that all the
members of this family are aggregates formed by the gravitational
re-accumulation of smaller fragments, and that certain of them could have
been ejected on trajectories that cross the Earth's trajectory. Since those
families that are already known and the oldest families share similar
properties, the authors suggest that they are likely to have had a similar
history.

This information concerning the internal structure of large asteroids also
has consequences for the impact energy that would destroy them. This is
useful not only to estimate the lifetime of these objects in the asteroid
belt, but also in order to develop strategies that aim to redirect such a
potentially dangerous asteroid.

Reference:
P. Michel, W. Benz & D.C. Richardson, Disruption of fragmented parent bodies
as the origin of asteroid families, Nature Vol. 421, 608-611, 2003.

For more information about asteroid collisions, see: Press release dated
November 22, 2001
http://www.cnrs.fr/cw/en/pres/compress/collisionsAsteroides.htm

=============
(4) NEW MOONS FOR JUPITER

>From BBC News Online, 6 March 2003
http://news.bbc.co.uk/1/hi/sci/tech/2825507.stm

By Dr David Whitehouse
BBC News Online science editor 

Astronomers have announced the discovery of yet another new batch of moons
in the Solar System - this time around Jupiter.
 
The new satellites bring Jupiter's tally to 47 compared with 30 for Saturn,
the planet with the second most number of moons.

Jupiter's new satellites were discovered in early February 2003 by Scott
Sheppard and David Jewitt of the University of Hawaii, US, working with Jan
Kleyna of Cambridge University, UK.

They were found using the world's two largest digital cameras at the Subaru
Telescope (8.3-metre diameter) and the Canada-France-Hawaii (3.6-metre
diameter) telescopes on Mauna Kea in Hawaii.

The satellites were formally announced to the astronomical community on 4
March.
 
The new moons are all small; two to four kilometres in size, and orbit
Jupiter at great distances from the planet.

Two of the seven new satellites (S/2003 J1 and S/2003 J6) have an orbit
around Jupiter that is in the same direction as Jupiter's spin).

The other five have distant so-called retrograde orbits like the majority of
the known irregular satellites of Jupiter.

Copyright 2003, BBC

============
(5) NEWTON WAS NOT A PROPHET OF DOOM

The Daily Telegraph, 4 March 2003
http://www.telegraph.co.uk/opinion/main.jhtml?view=HOME&grid=P18&menuId=-1&menuItemId=-1&_requestid=242444

Sir - I regret that your report (Feb 22) on Isaac Newton's beliefs failed to
put them into any historical context.

What is noteworthy about recent research is not that Newton was an
"apocalyptic" thinker: all Protestant scholars in 17th-century Britain held
such views. The apocalyptic consensus is not difficult to understand, given
that any departure from the literal reading of the Book of Revelation was
considered heresy.

Edmond Halley, who was confronted with this accusation in 1691, presented
papers to the Royal Society on "the necessity of the world's coming to an
end", to prove "that I am not guilty of asserting the eternity of the
world".

In Newton's days nearly everyone believed in heavenly retribution and the
catastrophic end of the world. The Church worked hard to scare an
insubordinate flock, while political radicals prophesied cometary disaster
and social upheaval.

Newton, in contrast, kept publicly quiet on the subject for most of his
life. He endeavoured to discredit both camps by debunking their shared
belief in impending doomsday.

In the unpublished manuscripts referred to, Newton did ponder the end of the
world "in the year of the Lord 2060", but stressed: "I mention this period
not to assert it, but only to show that there is little reason to expect it
earlier, and thereby to put a stop to the rash conjectures of interpreters
who are frequently assigning the time of the end, and thereby bringing the
sacred prophecies into discredit as often as their conjectures do not come
to pass. It is not for us to know the times and seasons which God hath put
in his own breast."

By pushing back a tentative date for the apocalypse by more than 500 years
(if not advocating an indefinite point in time), Newton assailed both an
over-zealous orthodoxy and political radicals whose fanaticism had led to a
century of mayhem and who threatened the stability of British society. Far
from being a prophet of doom, Newton calculatingly established the
foundations of the scientific age that turned terrifying comets into
predictable objects and wild fear-mongering into dispassionate risk
analysis.

Dr Benny Peiser
Liverpool John Moores University

============
(6) FIREBALL OVER CENTRAL CANADA

>From CNews, 5 March 2003
http://www.canoe.ca/NationalTicker/CANOE-wire.Green-Fireball.html

Ontario, Quebec police get calls of "green things" in sky; likely a fireball

TORONTO (CP) -- A green blaze that streaked through the skies over Central
Canada on Wednesday night, promoting curious and concerned calls to police,
was likely a fireball.

Richard Huziak, a member of the Royal Astronomical Society, said it sounded
like people were treated to a bright meteor or fireball.

"It sounds like basically some sort of major natural fireball. It's not
unusual to have fireballs," Huziak said Wednesday night.

Green is the most prominent colour of the fireballs, which are brighter than
any celestial object other than the moon and sun, according to the
Meteorites and Impacts Advisory Committee, a branch of the Canadian Space
Agency.

The fireballs are often the size of a small car, Huziak said.

Because of their relatively large size, sometimes they can burn brightly
enough to even turn off streetlights as they pass, he added.

Quebec provincial police got phone calls Wednesday night describing a bright
object that flew through the sky for two to three seconds before
disappearing in a final burst of light.

Reports of seeing "several green things in the sky" are intriguing because
it might mean multiple fireballs or that the fireball fragmented. But
multiple fireballs are unlikely.

"A few reports need to come in for this event to be characterized for
certain," he said. "Most people never see one in a whole lifetime."

Copyright 2003, CNews
 
===========
(7) HANDLE WITH CARE: METEORITES STRIKE YATINUWARA AND WENNAPPUWA

>From Sunday Observer (Cylon ), 2 March 2003
http://www.sundayobserver.lk/2003/03/02/new22.html

by ANTON NONIS

The 2.5 kilogram meteorite which struck Kalugalatenna estate in Muruthalawa,
Yatinuwara at approximately 11 pm on Wednesday has made many wonder whether
the predictions of Lalith Wijewardene, a gemmologist from Matara, have
finally come true. The strike in Yatinuwara was preceded by a strike in
Wennappuwa on February 8 but was smaller.

Three months ago Wijewardene predicted that a meteorite would strike a paddy
field or abandoned land at Nittambuwa in the Gampaha District. Although the
actual site was a few kilometres away in Wennappuwa, many say he can take
credit for predicting the event.

The February 8 meteorite strike was witnessed by Rosemary Jacinta, a
resident of the area. She had heard a sound similar to that of a leak in a
gas cylinder which had persisted for about a minute.

Colombo Campus Senior Physics lecturer Dr. Chandana Jayaratne told the
`Sunday Observer' that the object was clearly a meteorite and not any debris
from a satellite or the recently-destroyed American-Columbia spacecraft as
thought by some.

The object measured 2.5 centimetres in one direction and 1.6 cm in the other
and was of a stone-type substance.

Dr. Jayaratne has sent a portion of the meteorite to the National
Aeronautics and Space Administration NASA) for a thorough investigation. On
the following day the Air Force reported that one of its Kafir jets was hit
by an object while the aircraft was flying in the Wennappuwa area at a
height of 15,000 feet, damaging one of the plane's window pane. Some suspect
that the object could have been a meteorite striking the plane and are
wondering whether there was any link with the previous day's incident. The
pilot had not suffered injury.

According to Dr.Jayaratne, arrangements are being made to send a part of the
meteorite that struck Yatinuwara to NASA for examination.

Dr. Jayaratne said that meteorites may strike either singly or in packs.
These strikes may persist for more than a day at times which goes to explain
the hit on the Kafir jet on February 8.

Meanwhile, Wijewardene claims that his predictions of earthquakes have also
come true. These include Gujarat and Bangladesh in January, 2001, and
another in Iraq.

Wijewardene has also predicted an earthquake occurring in Sri Lanka this
year in the triangular area bordering Kotahena and Galle Face up to
Moratuwa. He says that the earthquake would be of considerable magnitude and
the tremor would be felt along the coastal belt in the triangle up to a
considerable distance.

However, geologists dismissing the predictions say that no earthquake has
ever been predicted. Nimal Ranasinghe of the directorate of Geological
Survey and Mines Bureau explained that Wijewardene's prediction was
surprising. "Predictions cannot be proved scientifically", he said. He also
dismissed the meteorite strike as a 'mere coincidence'.

Wijewardene is not able to explain how he made such predictions, He says it
could be an 'inborn talent' in him.

Copyright 2003, The Associated Newspapers of Ceylon Ltd.
 
===========
(8) MEETING ON ASTEROIDS AND COMETS IN EUROPE

>From Stephen Laurie <stephen@laurieco.com>

MACE 2003 - MEETING ON ASTEROIDS AND COMETS IN EUROPE
May  1-4   Costitx, Mallorca island, (Spain)
-Second Announcement and Call for Papers-
-------------------------------------------------------------

The "Meeting on Asteroids and Comets in Europe", MACE 2003, will be held
from May 1st to 4th at the Mallorca Observatory in Spain. If you are
planning to attend and have not yet "registered",
please do so now. For this, you just have to write an email to:
mace2003@oam.es with the following details

First name:
Last name:
Institution/Observatory:
E-mail:
Comments and suggestions:

Please be reminded that the deadline for abstract submission is April 1st.

For more details please visit:
http://www.oam.es/oam/mace/intro.htm

The goals of the meeting are:

- To improve the technology and techniques of observing.
- To search for goals of small observatories in the future.
- To continue and improve the relations and the established projects.
- To connect to other observers over borders and language barriers.

The scientific programme will include invited, contributed talks and
posters.  
The topics that will be covered at MACE 2003 include:
 
- Projects and scientific results on minor planets.
- Advances in telescope design.
- Observing methods and future projects for small observatories.
- Robotic and remote observation and tools for reduction data.
 
Also some observational and data reduction "live" sessions are planned. 

The Scientific and Local Organizing Committee has proposed the following
tentative programme:

PROGRAMME

>From evening of April 30, 2003 to May 1, at 12:00

Arrivals at Mallorca airport and free shuttle to the hotels in Port Alcudia.
Accomodation.

May 1, Thursday

13:00 - Welcome reception. Official opening.
13:30 - Welcome cocktail and lunch
15:00 - Invited talk
15:30 - Talks 1
17:00 - Cofee Break
17:30 - Talks 2
20:00 - Dinner - Video projection: MACE 2002 farewell dinner!
22:00 - Transport to hotels

 May 2, Friday

09:00 - Transport from hotels to meeting room
09:45 - Invited talk
10:15 - Talks 3
11:15 - Cofee break
11:45 - Talks 4
13:30 - Lunch
16:00 - Visit to the observatory of Mallorca and the Planetarium
16:30 - Audio-visual at the planetarium:  observing tools at the 
        Obs. of Mallorca
18:30 - Round table: observing and data processing tools
20:00 - Dinner
22:00 - Observing session
01:00 - Shuttle to hotels every hour

 May 3, Saturday

10:00 - Transport from hotels to the meeting room
10:45 - Invited talk
11:15 - Talks 5
13:30 - Lunch
16:00 - Excursion - Valldemossa and Serra de Tramuntana
21:00 - Closing Dinner
01:00 - Shuttle to hotels every hour

May 4, Sunday

Departures. Shuttles from hotels to the airport of Mallorca. Possibly half
day excursion to Palma, for participants departuring Sunday evening.

SCIENTIFIC ORGANIZING COMMITTEE

Luciano Bittesini   (Farra d'Isonzo Observatory) Italy
Korado Korlevic   (Visnjan Observatory) Croatia
Stephen Laurie   (Church Stretton Observatory) England
Jaime Nomen   (OAM-Mallorca & Ametlla de Mar Observatories) Spain
Petr Pravec   (Ondrejov Observatory) Czech R.
Herbert Raab   (Linz Observatory)  Austria
Jure Skvarc   (Crni vrh Observatory) Slovenia
Stefano Sposetti   (Gnosca Observatory) Switzerland
Reiner Stoss   (Starkenburg Observatory) Germany
Juraj Toth   (Modra Observatory) Slovakia

LOCAL ORGANIZING COMMITTEE

Oscar Arratia   (NEODyS team) Spain
Manolo Blasco   (OAM-Mallorca Observatory) Spain
Vadim Burwitz   (Max Planck institute & OAM-Mallorca Observatory)
Antonio Garcia   (OAM-Mallorca Observatory) Spain
Joan Guarro   (OAM-Mallorca & Piera Observatories) Spain
Jose-Luis Ortiz   (Instituto de astrofisica de Andalucia) Spain
Gabriel Pieras   (Consell of Mallorca) Spain
Juan Rodriguez   (OAM-Mallorca Observatory) Spain
Salvador Sanchez   (OAM-Mallorca Observatory) Spain
Genny Sansaturio   (NEODyS team) Spain

MEETING OFFICE

OAM-Observatorio Astronomico de Mallorca
Cami del Observatori s/n
Costitx, 07144 Mallorca
Spain
mace2003@oam.es

Tel:   34-689686557
        34-971876019
Fax:  34-971876022

MEETING VENUE

MACE 2003 will be held in the Civic Center  of the village of Costitx, very
close to the Observatorio Astronomico de Mallorca, however, some
observational sessions will take place at the
Observatory and the Planetarium.

============================
* LETTERS TO THE MODERATOR *
============================

(9) TECHNIQUES FOR ESTIMATING THE RISK OF SMALL AND MEDIUM IMPACTS: HOW
ACCURATE ARE THEY?

>From E.P. Grondine <epgrondine@hotmail.com>

Hello Benny -

As you might imagine, I have been following the recent discussion between
Don Yeomans, Clark Chapman, Allan Harris, Joe Veverka and yourself with some
interest. Reading the transcript, one of the things which really strikes me
is how often "estimates" of the risks to mankind from small and medium
impacts of both asteroids and comets are presented as being "facts", without
any discussion of exactly how those estimates were arrived at, or how
reliable those estimates are. Given the consequences of those estimates,
perhaps they should be discussed a little more fully, and thus this note.
What follows represents only my best understanding of the situation, and
given both my abilities and the width of the field, it is likely that it is
flawed. I offer it here only as a basis for further discussion.

ESTIMATES OF THE RISKS OF SMALL AND MEDIUM IMPACT BY CRATER COUNTING

There are several techniques for arriving at estimates of small and medium
impact, those types of impact most likely to occur within our lifetimes. The
first of these techniques, of course, is simply counting the craters on the
surfaces of some of the other bodies in our solar system. On some of those
bodies, unlike the case on our Earth, there are no geological processes
which rapidly remove the signs of small and medium impact.

I believe that the first time the crater counting method of estimation was
used was by Gene Shoemaker, who due to funding limitations based his
estimates on only a small part of the limited set of low resolution lunar
imagery which was available to him in the early 1960's. It is now 2003, and
it is amazing that Shoemaker's estimates are still being used some 40 years
later, when much higher resolution imagery of the surfaces of many more
bodies is currently available.

Another amazing thing about Shoemaker's estimates is that they have never
been adjusted, at least to my knowledge, to include any correction for our
Moon's near-by large gravitational companion, the Earth. As my knowledge
here is limited, perhaps the Italian astrodynamic team is much more familiar
with this problem than I am, and could share with Conference participants
any insights they might have on it.

Further, as was demonstrated most recently by the work on the lunar impact
of 1954, the resolution of the lunar imagery which Shoemaker used was so bad
that it was possible to miss 20 kiloton impacts. From this one can conclude
that any estimates as to the small and medium impact hazard which was
derived from the earlier low resolution imagery is of a pretty limited
value.

Of course, the new Mars imagery could provide a way around both the problem
of resolution and the problem of gravitational companion, but to my
knowledge the efforts here are limited due to lack of funding. I was
informed several years ago that there was a German team looking in great
detail at a limited set of Mars imagery, but I have heard no results from
them yet, and do not know if they are even still being funded. Scott
Hubbard, the recently appointed Director of NASA's Ames Research Center, is
fully aware of the impact hazard, and had given a high priority to the
development of a computer program for automated crater counting on surface
imagery from any body in our solar system, including Mars. Sadly, Scott's
talents have quite rightly been re-allocated to the investigation of the
failure of the space shuttle Columbia, and there are likely to be no quick
answers there.

Finally, not only do we have new imagery of the surface of Mars, but thanks
to the Galileo team's magnificent efforts, we now have detailed imagery of
the surfaces of the planet sized moons orbiting Jupiter. I spoke with the
Galileo team, and to my knowledge, funding to count the craters in this
imagery is essentially $0.00.

Let me emphasis again that this is only my understanding of the situation;
perhaps there is a Conference participant who is active in work in this area
and who may take a few minutes to share his knowledge of it with us.

ESTIMATES OF THE RISKS OF SMALL AND MEDIUM IMPACT BY GEOLOGY

Of course, not all of the craters on the Earth have been subducted back into
the Earth's magma, or had their features erased by normal weathering
processes. Given the value of the hydrocarbons which appear to pool in the
fractures caused by these impacts, and the value of the rare metals which
some of these impactors have delivered, there has been quite a bit of work
done on the identification of the large impact craters preserved here on the
Earth.

As the number of large craters which have been identified has grown, several
problems have emerged.  The first of these, which we know from the research
done at Tunguska, is that the effects of small and medium impacts are
relatively quickly weathered away. Added to this is the fact that funding
for the geological investigation of the remains of small to medium impacts
is non-existent for the most part.

Since direct geological investigation of small and medium craters is not
funded, the only technique for estimating the risks of small and medium
impact by geology is by finding the larger craters and then "inferring" by
one means or another the small and medium impact risks.  Here techniques are
just now being developed for differentiating between asteroid and comet
impact as the cause of each of these large craters, and again, based on my
conversation with Dr Becker and her team, the funding for this varies from
extremely limited to non-existent.

ESTIMATES OF THE RISKS OF SMALL AND MEDIUM IMPACT BY ASTRONOMY

Of course, no telescope is currently able to reliably "see" the types of
bodies which cause small to medium impacts, those bodies 300-400 meters or
less in diameter. Thus estimates as to the populations of those smaller
bodies are currently based on the observations of the larger bodies. Feeding
the results of these observations of larger bodies into one or another of
the available mathematical "sampling" techniques, estimates have been formed
as to the total populations of these larger objects; those total larger body
population "estimates" have then been used to "infer" by one mechanical
means or another the total populations of smaller and medium bodies.

Given the reflectivity and orbits of "dead" comet fragments, both of which
make them for the most part unobservable, these small and medium impact risk
estimates are usually based solely on the observations of the larger
asteroids alone. Thus it is quite common to hear asteroid astronomers state
the risks of small and medium impact as being solely those due to the impact
of asteroids, speaking as though comets, their fragments, and their impacts
do not exist. Unfortunately, from the direct observation of the impact of
Comet Shoemaker-Levy 9 on Jupiter, we know that statements of the total risk
which speak only of that arising from asteroids are rather completely
without merit.

ESTIMATES OF THE RISKS OF SMALL AND MEDIUM IMPACT BY OBSERVATION OF UPPER
ATMOSPHERE IMPACT

The detonations caused by the impacts of very small bodies with the upper
atmosphere are regularly observed by early warning satellites. As the bodies
observed here are much smaller than those which cause small to medium ground
impacts, once again one or another means of inference has to be applied to
that data to generate any estimates as to the populations and risks arising
from those slightly larger bodies.

While this data provides some constraints on the estimates of the risks of
small and medium impact which have been formed by other methods, it is
common to hear this data used to support estimates which differ by nearly an
order of magnitude. Given these statements claiming support, one can
reasonably conclude that the upper atmosphere detonation data must be of
limited value in forming a reliable estimate as to the risk of small and
medium impact.

Work on de-classifying this data is well underway, as is work on
differentiating that data by causitive body, in other words the detonations
are being sorted out by parent asteroid type or by dead comet fragment.

ESTIMATES OF THE RISKS OF SMALL AND MEDIUM IMPACT BY ANTHROPOLOGY

Another method of estimating the risks of small and medium impact is by
anthropological techniques, in other words by retrieving from the historical
records the direct observations by man of earlier small and medium impacts,
and then attempting to confirm or deny those reports through field work by
teams of geologists and archaeologists. In other cases ancient
archaeological remains have been found which appear to have been the result
of small and medium impacts, and then attempts have been made to find
mentions of those events in the surviving historical records.

Due to the stench which this work acquired as a result of Velikovsky's
nonsense (and in my opinion here one must agree with Morrison), most
professionals avoid this area of research like the plague. Usually they have
entered into it only when the data before them will admit of no other
explanation, and quite literally forces them into considering impact as the
cause of that data. The professionals realize that if they do complete work
in the area, they will then face the problem of review by peers who share
the same prejudices which they themselves used to hold, and worse, review by
supposed experts who often make statements such as "... People are not
killed individually, or by the hundreds or even the thousands, by impacts."
Finally, since funding for work of this type is exactly zero, the
professionals face the realization that any research which they may consider
doing will have to be financed by other means.

I want to digress briefly here into an immediate example of the problems
involved in estimate by anthropology. Consider the case of the crater
recently recognized in Italy, which Steel has reported on to Conference
participants. Improving the reliability of the radio-carbon dating of this
impact would require sending another team to the area to recover more
samples, and then radio-carbon dating the samples themselves, all at
considerable cost.

As for text records of this event, if anyone here recalls my survey of this
period, there was a passing mention made there of text records which may
have bearing on it:  "The Andersons refer the reader to Notker Balbalus's
identification of the city involved as Cita Nuova in Istria via a citation
to Gertrud Bruning, Adamnans Vita Columbae und ihre Abteilung, Zeitschrift
fur Celtische Philologie volume XI, Halle, 1917, page 290.  By the
Andersons' use of this device, one might assume that this lead would be a
dead end, but that would depend on whether Istria was within the borders of
Italy between 563-597 CE. Also, the possibility exists of an impact by a
separate fragment of a common parent body, an impact which Balbalus may have
noted."

Recovering these possible text records would require first locating
Bruning's article, and then Balbalus's identification, and then a close
examination down to the manuscripts level of the texts underlying both.
Because of the rarity of all of these texts, this work would require
extensive travel, which there is no money to pay for; and of course the
chances of a skilled classicist actually receiving a salary to carry out any
of this work are essentially nil.

I suppose one could also consider as a part of this method of risk
estimation some of the work being done on ice cores and tree rings, where
experts have tried to find historical texts which might explain the data
which they have recovered in their samples. Here there is very good news, as
new ice cores have been recovered, and work on their analysis is proceeding
right along. In particular, these ice cores may throw additional light on
the events ca. 536 CE. Tree ring data is also being further developed, and
work continues on improving its accuracy.

A summary of some of the work being done in the recovery of small and medium
impacts by anthropological techniques may be found at:
http://abob.libs.uga.edu/bobk/ccc/ce091702.html

It is interesting to note that nearly every researcher who is involved in
researching historical impact events is fairly alarmed by the results coming
in. One explanation for this alarm may be the rather straight forward one
which Rob Britt called to our attention, which is that impact events are not
theoretical for these researchers. Another explanation for their alarm may
be that the observed recent small and medium impact rates appear to be much
higher than those predicted by the other risk estimation means outlined
above. While a part of this divergence in risk estimates may be due to the
recent encounter of the Earth with the Comet Encke, it is by no means
certain that the planet Earth is not simply entering into a period of
increased cometary activity.

This anthropological work is often rightly described as being based on half
preserved records in half understood languages. Unfortunately, as in so many
other areas of NEO research, funding here for improvement is essentially
non-existent, and there is currently little hope of funding for field teams
to confirm or deny the readings of the historical texts. By way of example,
to my knowledge no geological teams have ever investigated the well attested
impacts which occurred in the last century at Rio Curacao in the jungle of
Brazil and in the Rupununi region of British Guyana. Given this state of
affairs, there is little chance of funding for dedicated teams to
investigate either the reported destruction of the Bazas area of France in
580 CE, or the apparent destruction by impact ca. 800 CE of Key Marco,
Florida.

A COMPARISON OF THE COST EFFECTIVENESS OF THE DIFFERING TECHNIQUES FOR
ESTIMATING THE RISK OF SMALL AND MEDIUM IMPACTS

While the anthropological effects of small and medium impacts are of the
greatest personal interest to me, and while I have no hard absolute dollar
numbers to use as a basis for comparison, my first seat of the pants guess
is that the most cost effective way for getting firm estimates of the risks
arising from small and medium asteroid and comet impacts is going to be by
counting the craters seen in the new imagery being returned from Mars by the
Global Surveyor and Observor spacecraft. In comparison with any of the other
methods of small and medium impact risk estimation which were described
above, the method of crater counting appears to have the dual advantages of
being relatively cheap, as well as being incredibly accurate.

Speaking for myself, and in this I am unanimous, to quote Mrs. Rumboldt,
while we are awaiting those new crater counts, I will object to any attempts
made by anyone to present their risk "estimates" as being "facts", instead
of clearly identifying those "estimates" as being estimates, whatever the
method of estimation they have used to derive them. At the same time, I will
also most certainly object to any attempt made by anyone to use the results
of any one particular estimation technique to stifle work along any of the
other line of risk estimation set out above.

THE EFFECTIVNESS OF MITIGATION TECHNIQUES AGAINST SMALL AND MEDIUM IMPACT

In discussions of mitigation techniques there is usually a focus on
mitigating larger impactors, and there is seldom any mention made of the
efficiency of these mitigation techniques against small to medium impactors.

It can reasonably be asserted that simply taking shelter could provide some
protection against the smallest impactors, and that coastal evacuation could
provide a great deal of protection against impact mega-tsunami. Taking
shelter would require at least 45 minutes of warning as to the exact
location where the impact would occur; evacuating a coastal area would take
at least 2 to 3 days.

My guess is that both of these will require telescopes of far greater
capabilities than those currently being proposed. The construction of such
telescopes may have the additional benefit of being able prevent small to
medium impacts from triggering an accidental nuclear weapons exchange.
Perhaps the MSX space based system which Pete Worden has been advocating may
provide sufficient warning time, but so far I see no funding is sight for
it.

Skilled engineers in Russia: http://abob.libs.uga.edu/bobk/ccc/cc020701.html
have detailed programs for either ameliorating or preventing impacts by the
use of nuclear charges. While the restraints on this method of mitigation
are currently being rigourously examined by many teams, including that of Dr
Holsapple at the University of Washington, at this point in time there is no
breakdown of the efficiency by impactor types (metal, stoney metal, stoney,
carbonaceous chondrite) of differing diameters (100, 200, 300, 400 meters).
 
In other words, we currently do not have even a rough idea as to the
effectiveness of using nuclear charges against small to medium impactors.

In the debate, I was delighted to see those who have concerns about the
safety of having nuclear charges on hand to deal with potential impactors
state those concerns explicitly. While hundred megaton charges of the type
needed to deal with impactors are of limited military use, here again, as in
so many other areas, no funds are being spent on diplomatic efforts to
develop ways to ensure that any such charges will be stored safely, and not
diverted to terrorist or military use.

In the US, Dr. Mazanek's team at NASA's Langley Research Center has
developed a plan for mitigation by laser ablation, a technique which should
be effective against potential impactors of all classes and sizes:
http://rasc.larc.nasa.gov/rasc_new/CAPS/CAPS_Concept_Summary.pdf
and
http://www.space.com/businesstechnology/technology/lunar_caps_011212-1.html

Given all of this work, there is simply no excuse for anyone in the NEO
community to continue to propagate the fatalistic falsehood that nothing can
be done to prevent any impacts, even given the severe restraints which
Holsapple and others are exploring. Thus in closing this quick overview of
the techniques for estimating the risks arising from the impacts of small to
medium asteroid and comets, I have a small favor to ask of some of you
concerning techniques for impact mitigation.

I would very much appreciate it if certain members of the NEO community
would stop repeating the falsehood that there is nothing we can do to
prevent impact events, whether they are small (city killers), medium (nation
killers), or large (dinosaur killers). Having examined in some depth the
work being done here, my conclusion is that at this point in time such
statements of futility amount to very nearly little more than lying to the
public about the methods available for dealing with a threat which is of
concern to them.

Well, Benny, that's it.  As always, I remain...

Yours in Science,
Ed

==============
(10) AND FINALLY: THE END MIGHT BE NIGH IN 20 BILLION YEARS

>From Space.com, 6 March 2003
http://www.space.com/scienceastronomy/big_rip_030306.html

The Big Rip: New Theory Ends Universe by Shredding Everything

By Robert Roy Britt

A rather harrowing new theory about the death of the universe paints a
picture of "phantom energy" ripping apart galaxies, stars, planets and
eventually every speck of matter in a fantastical end to time.

Scientifically it is just about the most repulsive notion ever conceived.

The speculative but serious cosmology is described as a "pretty fantastic
possibility" even by its lead author, Robert Caldwell of Dartmouth
University. It explains one possible outcome for solid astronomical
observations made in the late 1990s -- that the universe is expanding at an
ever-increasing pace, and that something unknown is vacuuming everything
outward. 

The question Caldwell and his colleagues posed is, what would happen if the
rate of acceleration increased?

Their answer is that the eventual, phenomenal pace would overwhelm the
normal, trusted effects of gravity right down to the local level. Even the
nuclear forces that bind things in the subatomic world will cease to be
effective.

"The expansion becomes so fast that it literally rips apart all bound
objects," Caldwell explained in a telephone interview. "It rips apart
clusters of galaxies. It rips apart stars. It rips apart planets and solar
systems. And it eventually rips apart all matter."

He calls it, as you might guess, the Big Rip.

The standard view

Driving the known acceleration of the universe's expansion is a mysterious
thing is called dark energy, thought of by scientists as anti-gravity
working over large distances.

Conventional wisdom holds that the acceleration will proceed at a constant
rate, akin to a car that moves 10 mph faster with each mile traveled. With
nothing to cap the acceleration, all galaxies will eventually recede from
one another at the speed of light, leaving each galaxy alone in a cold, dark
universe within 100 billion years. We would not be able to see any galaxies
outside our Milky Way, even with the most powerful telescopes.

That's the conventional view, remarkable as it sounds.

The Big Rip theory has dark energy's prowess increasing with time, until
it's an out-of-control phantom energy. Think of our car accelerating an
additional 10 mph every half mile, then every hundred yards, then every
foot.

Before long, the bumpers are bound to fly off. Sooner or later, our
hypothetical engine will come apart, regardless of how much we spend on
motor oil.

Countdown to demise

Other theorists who have reviewed the Big Rip theory are not yet sold on the
idea. Meanwhile, Caldwell's team has provided a precise countdown to total
demise. The projected end is, reassuringly, 20 billion years away. If our
species survives the next 19 billion years (and there are serious doubts
about this, given our Sun's projected fate) here are some signs that
scientists of the future will want to look for.

A billion years before the end, all galaxies will have receded so far and so
fast from our own as to be erased from the sky, as in no longer visible.

When the Milky Way begins to fly apart, there are 60 million years left.

Planets in our solar system will start to wing away from the Sun three
months before the end of time.

When Earth explodes, the end is momentarily near.

At this point, there is still a short interval before atoms and even their
nuclei break apart. "There's about 30 minutes left," Caldwell said, "But
it's not quality time."

And then what? Does the universe recycle itself? Is there something after
nothing?

"We're not sure what happens after that," Caldwell says. "On the face of it,
it would look like time ends."

The first explosion

Caldwell's study had humble beginnings. He and his colleagues, Marc
Kamionkowski and Nevin Weinberg at Caltech, were considering how a sphere of
matter collapses under its own weight to form a galaxy. In computer models,
they tweaked with the dark energy factor and found that too much of it would
actually prevent the sphere from collapsing. In extreme cases, the sphere
exploded.

"That was our hint that there was something really unusual going on,"
Caldwell said.

It wasn't long ago, just before the accelerated expansion was discovered,
that many cosmologists believed the universe might reverse course, that
normal gravity would win, and that everything would fall back in a Big
Crunch. More recently, solid observational data has all but assured the
infinite-expansion model and the cold, dark, never-ending end.

The Caldwell group decided there might be a third possibility, leading to
their new paper, which has been submitted to the Physical Review.

But there are many unknowns. It is not clear if the dark energy driving
expansion is a force not currently described by physics, or if it is merely
a different manifestation of gravity over huge distances. The repulsion
could be a response to dark matter, unseen stuff that is known to comprise
23 percent of the universe, based on firm observations.

Dark matter has unknown properties, and it may be related to dark energy,
Caldwell said. He notes that even Einstein considered that gravity might
work repulsively, in a manner consistent with his theory of general
relativity.

Dark energy, being quantified only recently, tends to be discussed as some
strange new force, in addition to the four fundamental forces: gravity,
electromagnetism, and the strong and weak nuclear forces that govern atoms.
But the repulsion is possibly just the way gravity behaves in the presence
of dark energy, Caldwell said. In that sense, it is not a new force.

Cautious reception

To turn dark energy into destructive phantom energy, Caldwell and his
colleagues had to play around with a thing called the cosmological constant,
a mathematical fix that Einstein applied to general relativity. Einstein
later called it his greatest mistake, when Edwin Hubble found in the 1920s
that the universe was expanding (seven decades later, that expansion would
be seen accelerating).

The cosmological constant has been recently revived. Attempts to describe
dark energy differ in how the density of dark energy varies with time. In
some models, the density decreases slowly. For the cosmological constant,
the density is a constant. For phantom energy, it must grow with time.

"We considered a more exotic form of dark energy which was more repulsive,"
as Caldwell explains is.

Abraham Loeb, a theoretician at the Harvard-Smithsonian Center for
Astrophysics, has quantified the lonely effects of a forever-expanding
universe. Loeb stands by that scenario, but he said Caldwell's idea is
nonetheless interesting to explore.

"I think it's a logical possibility," Loeb told SPACE.com. But he cautioned
that altering the cosmological constant goes against current consensus.

"If I had to place a bet, I would bet in favor of the standard cosmological
constant," Loeb said.

Sci-fi to reality

If Caldwell's team is right, cosmology would undergo a revolution. Sci-fi
ideas like wormholes and time travel might suddenly enter the realm of hard
science. All of this could sort itself out pretty soon, Caldwell believes.
Observations over the next few years may actually show whether his phantom
energy is possible.

"Who knows if it is right or wrong," Caldwell said of his theory. "I think
we'll find out pretty soon."

In fact, recent observations from NASA's WMAP space probe have pinned down
the physics of the universe with surprising accuracy. A little wiggle room
remains for the cosmological constant. Yet more WMAP data are expected over
the next four years. Other missions, including one called the Supernova
Acceleration Probe (SNAP), could provide answers, Caldwell said.

Even if the Big Rip is a big bust, there's no guarantee of a pleasant
ending.

Alternate final chapter

Paul Steinhardt, a Princeton University physicist, is, like Caldwell and
Loeb, no stranger to strange ideas. Steinhardt advocates a cyclical
universe, one that has no beginning or end but which instead is constantly
starting over again.

Steinhardt theorizes within the generally accepted standards of the
cosmological constant. He said the Big Rip is more exotic than most ideas
but still conceivable, a projected possible result that is "straightforward
and obvious for cosmologists."

Yet there is another entirely different possibility for the final moments of
time as we know it.

In a theory put forth two years ago by Steinhardt and his colleagues, our
universe is but a membrane, or brane, floating in a five-dimensional space.
It is destined to collide dramatically with another brane. The idea, labeled
the Ekpyrotic Universe, would replace portions of the Big Bang scenario
while sticking to the presently accepted estimates of acceleration.

"Lest you get too optimistic, galaxies are destroyed in a far more violent
way," Steinhardt said of the brane scenario. "They are vaporized at the next
'bang' -- the collision between branes ... so, you either rip them apart or
you vaporize them."

Copyright 2003, Space.com

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*

CCNet, 25/2003 -  7 March 2003
------------------------------


"Dust dumped over New Zealand by the central American impact said to
have killed the dinosaurs [amounts] to not much more than what you
would find in your house if you didn't clean for a weekend or two. The
[meteor] impact theory is largely driven by American imagination."
--Gordon Lister, Monash University, 5 March 2003


"What isn't settled is just what was going on 3.2 billion years ago
to cause three great impacts in just 20 million years. Were asteroid
impacts more common throughout the early history of the Earth or was
this just a spike of impacts?"
--Larry O'Hanlon, Discovery News, 4 March 2003



(1) HUGE ASTEROID IMPACTS PREDATE DINOS
    Discovery Channel, 4 March 2003

(2) THE OLDEST RECORD OF EARLY ARCHAEAN IMPACTS
    Geology: Vol. 31, No. 3, pp. 283-286

(3) NASA RELEASES IMAGE OF CHICXULUB CRATER CREATED BY MASSIVE SPACE ROCK
    Knight Ridder Newspapers, 6 March 2003

(4) SHADED RELIEF IMAGE OF MEXICO'S YUCATAN PENINSULA
    Planetary Photojournal, 6 March 2003

(5) IMPACT WORKSHOP
    Charles Cockell <csco@bas.ac.uk>

(6) AUSTRALASIAN MICROTEKTITES IN THE SOUTH CHINA SEA: IMPLICATIONS
REGARDING THE LOCATION AND
    SIZE OF THE SOURCE CRATER.
    B.P. Glass

(7) NUMERICAL MODELING OF MARINE IMPACTS
    J Ormo et al.

(8) THE SUDBURY STRUCTURE: A CIRCULAR IMPACT CRATER?
    WA Morris

(9) AND FINALLY: NUTTY PROFESSOR: "K/T IMPACT THEORY LARGELY DRIVEN BY
AMERICAN IMAGINATION"
    Sydney Morning Herald, 5 March 2003


==========
(1) HUGE ASTEROID IMPACTS PREDATE DINOS

>From Discovery Channel, 4 March 2003
http://c.moreover.com/click/here.pl?e62993760&e=6513     

By Larry O'Hanlon, Discovery News

March 4, 2003 - The three most terrible asteroid impacts in the Earth's
history are also the oldest, say geologists working on frozen blobs of
melted rock ejected from impacts more than 3.2 billion years ago.

Any craters from the impacts were erased long ago by Earth's everchanging
crust. What does remain, however, are deposits of rock spherules in South
Africa's Barberton Greenstone Belt region that were once a fiery rain of
molten material blasted from horrific impacts.

"The bottom line is that I think they were bigger than the K/T impact," said
geologist Frank Kyte of the University of California at Los Angeles,
referring to the impact of a ten-kilometer (seven-mile) wide asteroid that
killed the dinosaurs 65 million years ago.

Kyte and a number of other asteroid impact researchers published their
report in the March issue of the journal Geology.

Since they were discovered in 1986, the South African spherules have sparked
scientific debate over whether they were caused by impacts or some purely
earthbound process. The work by Kyte and his colleagues might finally settle
the debate because they have found in the spherules something only found in
extraterrestrial rocks - an unusual abundance of a rare type of chromium.

For reasons that are buried in the early history of the solar system,
meteorites tend to have more chromium-53 and chromium-54 than rocks from the
Earth, moon or Mars, which tend to have more chromium-52 (Martian meteorites
supplied the information about Mars).

Using a new and painstaking technique to analyze the South African
spherules, Kyte and his colleagues were able to determine that the rocks
contained amounts of chromium-53 and chromium-54 that pegged them as
relatives of a relatively rare kind of meteorite, a carbonaceous chondrite.

Factors they used to estimate the size of the asteroids that spawned the
spherules include the thickness of the spherule beds and the likely
assumption that the debris rained down over the entire Earth. All that seems
to indicate that the Archean asteroids ranged from one to seven times the
size of the K/T asteroid.

In other words, the discovery not only confirms the impact origins of the
rocks, but it suggests that the asteroids 3.2 billion years ago were a bit
different than those that are common today, said planetary scientist Alan
Hildebrand of the University of Calgary.

They are rough estimates, based on comparisons to similar beds from the much
better preserved K-T impact. Factors they used to estimate the size of the
asteroids include the thickness of the spherule beds and the likely
assumption that the debris rained down over the entire Earth. All that seems
to indicate that the Archean asteroids ranged from one to seven times the
size of the KT asteroid.

"In my opinion this is quite a significant result," said Hildebrand. "It
should settle the debate on origins."

What isn't settled is just what was going on 3.2 billion years ago to cause
three great impacts in just 20 million years. Were asteroid impacts more
common throughout the early history of the Earth or was this just a spike of
impacts?

Only the discovery of more such spherules of other ages will tell, said
Kyte.

Copyright © 2003 Discovery Communications Inc.

===========
(2) THE OLDEST RECORD OF EARLY ARCHAEAN IMPACTS

>From Geology: Vol. 31, No. 3, pp. 283-286
http://www.gsajournals.org/gsaonline/?request=get-document&issn=0091-7613&volume=031&issue=03&page=0283

Early Archean spherule beds: Chromium isotopes confirm origin through
multiple impacts of projectiles of carbonaceous chondrite type

Frank T. Kyte
Center for Astrobiology, Institute of Geophysics and Planetary Physics,
University of California, Los Angeles, California 90095-1567, USA

Alex Shukolyukov
Scripps Institution of Oceanography, University of California, San Diego, La
Jolla, California 92093-0212, USA

Günter W. Lugmair
Scripps Institution of Oceanography, University of California, San Diego, La
Jolla, California 92093-0212, USA, and Max-Planck Institute for Chemistry,
Cosmochemistry, P.O. 3060, 55020 Mainz, Germany

Donald R. Lowe
Department of Geological and Environmental Sciences, Stanford University,
Stanford, California 94305, USA

Gary R. Byerly
Department of Geology and Geophysics, Louisiana State University, Baton
Rouge, Louisiana 70803-4101, USA

Manuscript Received by the Society 23 May 2002
Revised Manuscript Received 22 October 2002
Manuscript Accepted 23 October 2002

ABSTRACT

Three Early Archean spherule beds from Barberton, South Africa, have
anomalous Cr isotope compositions in addition to large Ir anomalies,
confirming the presence of meteoritic material with a composition similar to
that in carbonaceous chondrites. The extraterrestrial components in beds S2,
S3, and S4 are estimated to be 1%, 50%-60%, and 15%-30%, respectively. These
beds are probably the distal, and possibly global, ejecta from major
large-body impacts. These impacts were probably much larger than the
Cretaceous-Tertiary event, and all occurred over an interval of 20 m.y.,
implying an impactor flux at 3.2 Ga that was more than an order of magnitude
greater than the present flux.

Keywords: Archean, impacts, spherules, iridium, 5352.

INTRODUCTION

The oldest record of major impact events on Earth may be a number of Early
Archean (3.5-3.2 Ga) spherule beds in the Barberton greenstone belt, South
Africa. Lowe and Byerly (1986) first proposed that single spherule beds
found in the Barberton greenstone belt, and in the Eastern Pilbara block,
Western Australia, were derived from quenched silicate droplets formed by
major impact events. Other workers (de Wit, 1986 ; French, 1987 ; Buick,
1987 ) argued that an impact origin was unlikely and proposed that the
spherules could be from erosion of volcanic materials. Further work by Lowe
et al. (1989) found that at least four spherule beds (labeled S1-S4) occur
in the Barberton greenstone belt and that some specimens are enriched in Ir
and other platinum group elements (PGEs). They cited seven specific criteria
that distinguish these beds from normal clastic sediments, including the
wide geographic distribution of two beds across a variety of depositional
environments, presence of relict quench textures and Ni-rich spinels within
the spherules, absence of juvenile volcaniclastic debris, and extreme
enrichment of Ir and other PGEs. Kyte et al. (1992) reported detailed
analyses of four PGEs (Ir, Os, Pt, Pd) and Au in bed S4 and found Os/Ir and
Pt/Ir ratios within 20% of chondritic abundances. Although Pd and Au in S4
were depleted relative to chondrites by 59% and 98%, respectively, this is
opposite to the effect expected by Au mineralization and was attributed to
regional hydrothermal alteration of originally chondritic material. Byerly
and Lowe (1994) showed that chemical compositions of Ni-rich spinels in
spherules are unique and distinct from those in komatiites and other
volcanic rocks. These spinels are now recognized to occur only in spherules
from bed S3 (Lowe et al., 2003 ). Some researchers, however, still argued
for a terrestrial origin, possibly related to volcanism and gold
mineralization (Koeberl and Reimold, 1995 ; Reimold et al., 2000 ). They
analyzed samples from the vicinity of gold mines in the northern Barberton
greenstone belt and found extreme enrichments of Ir, a result they found
difficult to reconcile with an impact origin.

Work on the 53Mn-53Cr isotope systematics in various solar system objects
(Lugmair and Shukolyukov, 1998 ) has provided a method for unequivocally
demonstrating an extraterrestrial component in impact ejecta with high
concentrations of meteoritic Cr. All meteorite classes studied so far have
excess 53Cr relative to terrestrial samples. This fact reflects an early
Mn/Cr fractionation and possibly heterogeneous distribution of the
now-extinct parent radionuclide 53Mn (half-life, t1/2 = 3.7 m.y.) in the
early solar system. The carbonaceous chondrites also have an excess of 54Cr,
due to a presolar component, in addition to excess 53Cr (Shukolyukov and
Lugmair, 2000 , 2001 ). Thus, precise measurements of Cr isotope abundances
can distinguish terrestrial from extraterrestrial materials and the
carbonaceous chondrites from other meteorite groups. This method provided
the first isotopic proof that the Cretaceous-Tertiary (K-T) boundary
contains meteoritic materials (Shukolyukov and Lugmair, 1998 ). We have
applied this method to several spherule bed samples. In our initial study
(Shukolyukov et al., 2000 ) we found anomalous Cr isotope abundances in bed
S4. We now report that three spherule beds-S2, S3, and S4-are all enriched
in extraterrestrial Cr.

FULL PAPER at
http://www.gsajournals.org/gsaonline/?request=get-document&issn=0091-7613&volume=031&issue=03&page=0283

=============
(3) NASA RELEASES IMAGE OF CHICXULUB CRATER CREATED BY MASSIVE SPACE ROCK

>From Knight Ridder Newspapers, 6 March 2003
http://www.siliconvalley.com/mld/siliconvalley/news/5332512.htm

By Robert S. Boyd
Knight Ridder Newspapers

WASHINGTON - A NASA space shuttle has taken the first aerial picture of the
crater left by the monster comet or asteroid that most scientists believe
doomed the dinosaurs to extinction 65 million years ago.

The image shows part of the outer rim of the 112-mile-wide Chicxulub
(pronounced CHICK-soo-lube) crater on the northwest corner of Mexico's
Yucatan Peninsula. It's a semicircular trough, 10 to 15 feet deep and 3
miles wide, the surface evidence of what was once a 3,000-foot-deep gouge in
the Earth.

"If you walked across it, you probably wouldn't notice it. That's where the
view from space becomes invaluable," said Michael Kobrick, project manager
for NASA's Shuttle Radar Topography Mission.

For 10 days in February 2000, the shuttle Endeavor used a radar instrument
to trace the ups and downs on 80 percent of the Earth's landmass. It brought
back 200 billion detailed, 3-D measurements, which have since been analyzed
and turned into a high-resolution map of North America that NASA released on
Thursday.

"There are spectacular features that pop out in these maps as never before,
and more subtle features, like Chicxulub, become apparent for the first
time," Kobrick said.

In the 1980s, scientists began to suspect that a huge space rock had smashed
into what is now the Caribbean Sea. By the 1990s, most were convinced that
this was the "smoking gun" responsible for the extinction of the dinosaurs
and 70 percent of the species then living on Earth.

Exactly what caused the mass extinction is not known. Likely explanations
include huge dust clouds that blocked the sun and crippled plant growth for
years; sulphur clouds that fell as worldwide acid rain and global firestorms
ignited by the red-hot debris kicked up by the collision.

It must have been "one of the Earth's worst days," said Alan Buis, spokesman
for NASA's Jet Propulsion Laboratory in Pasadena, Calif., which manages the
project.

---
For more information:
NASA images are available at
http://photojournal.jpl.nasa.gov/catalog/PIA03379

============
(4) SHADED RELIEF IMAGE OF MEXICO'S YUCATAN PENINSULA

>From Planetary Photojournal, 6 March 2003
http://photojournal.jpl.nasa.gov/catalog/PIA03379

PIA03379: Shaded Relief with Height as Color, Yucatan Peninsula, Mexico   

Target Name: Earth
Is a satellite of: Sol (our sun)
Mission: Shuttle Radar Topography Mission (SRTM)
Spacecraft: Space Shuttle
Instrument: C-Band Interferometric Radar
Product Size: 18001 samples x 11438 lines
Produced By: JPL
Full-Res TIFF: PIA03379.tif (617.7 megabytes) 

Original Caption Released with Image:

This shaded relief image of Mexico's Yucatan Peninsula show a subtle, but
unmistakable, indication of the Chicxulub impact crater. Most scientists now
agree that this impact was the cause of the Cretatious-Tertiary Extinction,
the event 65 million years ago that marked the sudden extinction of the
dinosaurs as well as the majority of life then on Earth.
Most of the peninsula is visible here, along with the island of Cozumel off
the east coast. The Yucatan is a plateau composed mostly of limestone and is
an area of very low relief with elevations varying by less than a few
hundred meters (about 500 feet.) In this computer-enhanced image the
topography has been greatly exaggerated to highlight a semicircular trough,
the darker green arcing line at the upper left corner of the peninsula. This
trough is only about 3 to 5 meters (10 to 15 feet) deep and is about 5 km.
wide (3 miles), so subtle that if you walked across it you probably would
not notice it, and is a surface expression of the crater's outer boundary.
Scientists believe the impact, which was centered just off the coast in the
Caribbean, altered the subsurface rocks such that the overlying limestone
sediments, which formed later and erode very easily, would preferentially
erode on the vicinity of the crater rim. This formed the trough as well as
numerous sinkholes (called cenotes) which are visible as small circular
depressions.

Two visualization methods were combined to produce the image: shading and
color coding of topographic height. The shade image was derived by computing
topographic slope in the northwest-southeast direction, so that northwestern
slopes appear bright and southeastern slopes appear dark. Color coding is
directly related to topographic height, with green at the lower elevations,
rising through yellow and tan, to white at the highest elevations.

For a smaller, annotated version of this image, please select Figure 1,
below:

Elevation data used in this image were acquired by the Shuttle Radar
Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on
Feb. 11, 2000. SRTM used the same radar instrument that comprised the
Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR)
that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to
collect 3-D measurements of the Earth's surface. To collect the 3-D data,
engineers added a 60-meter (approximately 200-foot) mast, installed
additional C-band and X-band antennas, and improved tracking and navigation
devices. The mission is a cooperative project between NASA, the National
Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense and the
German and Italian space agencies. It is managed by NASA's Jet Propulsion
Laboratory, Pasadena, Calif., for NASA's Earth Science Enterprise,
Washington, D.C.

Size: 261 by 162 kilometers (162 by 100 miles)
Location: 20.8 degrees North latitude, 89.3 degrees West longitude
Orientation: North toward the top, Mercator projection
Image Data: shaded and colored SRTM elevation model
Original Data Resolution: SRTM 1 arcsecond (about 30 meters or 98 feet)
Date Acquired: February 2000

================
(5) IMPACT WORKSHOP

>From Charles Cockell <csco@bas.ac.uk>

Dear Friends,

There are just two days left for late registration for the 10th ESF
Workshop. The workshop, which will be held at King's College, Cambridge from
Sunday March 30th to Tuesday April 1 includes the following highlights :

- Two and a half days of talks on BIOLOGICAL PROCESSES ASSOCIATED WITH
IMPACT EVENTS. Abstracts will cover a diversity of interesting connections
on the general theme of impact cratering as a biological process. As well as
discussions of extinctions talks will cover survival of microbes during
impact, duration of hydrothermal oases on Titan, organic synthesis in impact
events and others.

- a Gala dinner at King's College with an IMPACT theme

- an open discussion opportunity to air your views and discuss ideas for
future IMPACT funding (remember this is the last workshop of the current
funding cycle. Now is your chance to demonsrate support by attending this
meeting and forging the path of this program). It is IMPORTANT that those
who support IMPACT attend this workshop!

- Reception at the University of Cambridge Sedgwick Museum

Please pass this e-mail to others who may be interested in attending this
event.

Information at :  http://pssri.open.ac.uk/ESF/

________________________
Dr. Charles Cockell,
British Antarctic Survey,
High Cross,
Madingley Road,
Cambridge.
CB3 0ET. UK
Tel : + 44 1223 221560
e-mail : csco@bas.ac.uk

=========
(6) AUSTRALASIAN MICROTEKTITES IN THE SOUTH CHINA SEA: IMPLICATIONS
REGARDING THE LOCATION AND SIZE OF THE SOURCE CRATER. B. P. Glass, Geology
Department, University of Delaware, Newark, DE 19716, USA
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1092.pdf

Introduction: Australasian microtektites have been found in over 50 sites in
the Indian and western equatorial Pacific Oceans; the Philippine, Sulu, and
Celebes Seas; and more recently in the South China Sea [1-5]. Glass and
Pizzuto [2] used geographic variations in concentrations of microtektites
(number >125 µm dia./cm2) to predict the location of the source crater. The
location that explained the geographic distribution the best was 12E N, 106E
E. This location was supported by Lee and Wei [5] based on data from two
additional cores. Previous estimates of the source crater diameter range
from 17 to 114 km [2,5,6].

I report here additional microtektite/impact ejecta data for Core 17957-2
taken in the South China Sea (10E 53.9' N, 115E 18.3' E) during the SONNE-95
cruise [3]. I also report the discovery of abundant Australasian
microtektites and associated shockmetamorphosed grains in Ocean Drilling
Program (ODP) Hole 1144A, in the northern South China Sea (20E 3.18' N, 117E
25.14' E). ODP Site 1143 (9E 21.72' N, 113E 17.11' E) was also searched for
microtektites, but the layer was not found at this site. The new data from
Core 17957-2 and Hole 1144A, as well as from other Australasian
microtektitebearing sites, were used to reevaluate the location and size of
the source crater.

Core 17957-2: Nearly 3000 microtektites (>125 µm dia.) were recovered from
Core 17957-2. About
90% of the microtektites were found between 798 and 818 cm depth (i.e., a 20
cm interval), although scattered microtektites were found over a 2.25 m
interval. The peak abundance is at a depth of about 806 cm. Close to 55% of
the microtektites are splash forms (spheroids, teardrops, dumbbells, disks),
the remainder are fragments. The largest spheroid is ~880 µm in diameter.
The largest elongate form is 1.4 mm long and the largest fragment has a
maximum length of ~2.1 mm. Many of the fragments are larger than the largest
spheroid and exhibit no obvious original outer surface and, thus, may be
tektite fragments. Unmelted impact ejecta make up about 20% of the ejecta in
the microtektite layer. The most obvious unmelted ejecta are white opaque
grains consisting of mixtures of quartz, coesite, and traces of stishovite
(and probably lechatelierite). Numerous shocked-rock fragments are also
present and X-ray diffraction (XRD) studies indicate that they generally
consist of coesite, quartz, stishovite(?), and a clay/mica phase. The
maximum length of the largest shocked-rock fragment is ~1 mm. I estimate
that the number of microtektites and unmelted ejecta (>125 µm) per cm2 at
this site is 2918 and 814, respectively.

ODP Hole 1144A. The microtektite layer at this site was found in Core 37x,
Section 6. More than 90% of the microtektites were found between 61 and 71 cm with the peak
abundance at ~68 cm depth (~345.68 m below the sea floor). Scattered microtektites were found over a
1.46 m interval. The total number of recovered microtektites was 18,189.
About 75% are fragments, the remainder is splash forms. A small percent of
the glass is highly vesicular with a frothy appearance. In addition, a few,
dark, translucent to opaque, heterogeneous blebs of normal impact glass were
recovered. Unmelted ejecta make up 44% of the total impact ejecta. Roughly
20% (by number) of the unmelted ejecta are white opaque grains, which
according to XRD studies, contain various proportions of quartz, coesite,
and stishovite (and presumably lechatelierite).

One appears to be pure stishovite. Most of the rock fragments are light- to
dark-grey, equant, subangular to subrounded, and fined-grained (generally
<20 µm). XRD studies indicate that the rock fragments are mixtures of
quartz, coesite, and a mica/clay phase. At this site, the estimated number
of microtektites (>125 µm)/cm2 is 9834 and the estimated number of unmelted
ejecta grains (>125 µm)/cm2 is 7327. At the peak abundance level, impact
ejecta (including microtektites) make up >90 wt.% of the coarse (>125 µm)
fraction. Thus, Hole 1144A has the highest concentration of microtektites
(>3 time higher), the highest percent of fragments versus whole
microtektites, and the highest ratio of unmelted to melted ejecta of any
previously studied Australasian microtektite-bearing site. All of this
suggests that this site is closer to the source crater than any other site.

Predicted Source Crater Site and Size: The source area can be predicted by
assuming locations of hypothetical source craters and then regressing the concentrations of
microtektites at each core site versus the distance from the postulated
crater [2]. The location that gives the highest correlation coefficient (r2
value) indicates the location that explains the geographical variation in
microtektite concentrations the best. Using the microtektite concentrations
for Core 17957-2 and ODP Hole 1144A given above, as well as data from Glass
and Pizzuto [2] and Lee and Wei [5], indicate a source crater location near
15E N and 105E E with an r2 value of 0.86. This is 3E farther north and 1E
farther west than predicted by Glass and Pizzuto [2] and Lee and Wei [5],
but it is closer to the location predicted by Schnetzler [7] based on
geographical variations in composition of Muong Nong-type Australasian
tektites. However, any place in northern Cambodia, central Laos, or eastern
Thailand would explain the geographic distribution nearly well. ODP Hole
1144A is the closest microtektitebearing site to this location (~1430 km
away) which is consistent with the observations discussed above that
indicate that this site is closer to the source crater than any other
Australasian microtektite site.

The size of the source crater can be estimated based on equations that
relate the thickness of an
ejecta layer to the size of the source crater and distance from the source
crater (e.g., [8]). The concentrations of microtektites were first used to
estimate the thickness of the layer, prior to bioturbation, at each site (an
average microtektite diameter of 200 µm was used in the calculations). The
maximum thickness obtained was only ~800 µm. Using these thicknesses in the
equations of [8] indicate a source crater diameter of 33 ± 6 km (based on
eleven sites with the highest concentrations). If the unmelt ed ejecta at
Site 1144A are included in the estimate
of the ejecta layer thickness, the estimated size of the source crater
increases from 39 to 44 km. Unfortunately, concentrations of unmelted ejecta
at most other sites have not been determined, but appear to be too low to
make much of a difference. Comparison of microtek tite concentration versus
distance from the source crater between the Australasian strewn field and
the Ivory Coast and North American strewn fields with source craters of 10.5
km and 85 km in diameter, respectively, suggests that the Australasian
source crater is intermediate in size but probably closer to the size of the
North American source crater. Thus, a diameter of ~40 km appears to be a
reasonable estimate based on present knowledge. This is smaller than most
previous size estimates (e.g., [2,5,6]); however, this smaller size is more
in line with the apparent lack of any climatological and/or biological
effects of the impact responsible for the Australasian strewn field.

Acknowledgments: I thank Kevin M. Yezdimer for help processing core samples
from ODP 1144A,
the Ocean Drilling Program for core samples, and M. Sarnthein for samples
from Core 17957-2.

References: [1]Peng H. et al. (1982) JGR, 87, 5563.
[2]Glass B. P. & Pizzuto J. E. (1994) JGR, 99, 19,075.
[3]Zhao Q. et al. (1999) Sci. China Ser. D, 42 (2), 531.
[4]Wang J. et al. (2000) Chinese Sci. Bull. 45 (24), 2277.
[5]Lee M.-Y. & Wei K.-Y. (2000) MAPS, 35, 1151.
[6]Baldwin R. B. (1981) Icarus, 45, 554.
[7]Schnetzler C. C. (1992) Meteoritics, 27, 154.
[8]Stoffler D. (1975) JGR, 80, 4062.

============
(7) NUMERICAL MODELING OF MARINE IMPACTS

Ormo J, Shuvalov VV, Lindstrom M: Numerical modeling for target water depth
estimation of marine-target impact craters, JOURNAL OF GEOPHYSICAL
RESEARCH-PLANETS 107 (E12): art. no. 5120 DEC 5 2002

[1] Marine impacts can develop a crater in the seafloor if the target water
depth is shallow in relation to the size of the impactor. The geology of
this marine-target crater is influenced by the layer of water in the upper
part of the target. The influence increases with increased water depth. The
target water depth is essential when calculating the magnitude of the impact
event as the seafloor crater merely expresses some of the expended energy.
The target water depth for a marine-target crater is often estimated by
facies analysis of sediments related to the impact crater, unfortunately
often with ambiguous results. We propose to combine the conventional methods
with numerical modeling of the target water depth based on the special
target-water-related features of the crater. We used geological data from
the Lockne crater as constraints in a simulation with the SOVA hydrocode.
The simulations were done for three different target water depths (200 m,
500 m, and 1000 m) within the likely depth range for the Middle Ordovician
sea, in which the impact occurred. In order to obtain the minimum estimated
size of the Lockne crater by an asteroid impact at 20 km/s, the water depth
must have been slightly less than 1 km, and the impactor radius must have
been about 400 m. It was not possible to generate a crater with the
geological features of Lockne for target water depths of less than about 500
m. However, the ratio may be further constrained by factors such as impactor
density, impact angle, and impact velocity.

Addresses:
Ormo J, Inst Nacl Tecn Aerospacial, Ctr Astrobiol CSIC INTA, Ctr Torrejon
Ajalvir,Km 4, Madrid 28850, Spain
Inst Nacl Tecn Aerospacial, Ctr Astrobiol CSIC INTA, Madrid 28850, Spain
Inst Dynam Geospheres, Moscow 117334, Russia
Stockholm Univ, Dept Geol & Geochem, S-10691 Stockholm, Sweden

Copyright © 2003 Institute for Scientific Information

=============
(8) THE SUDBURY STRUCTURE: A CIRCULAR IMPACT CRATER?

Morris WA: The Sudbury Structure: A circular impact crater?, GEOPHYSICAL
RESEARCH LETTERS 29 (20): art. no. 2002 OCT 15 2002

[1] Petrological, geochemical, and structural evidence supports genesis of
the Sudbury Structure by a meteorite impact. The Sudbury Igneous Complex
(SIC) represents the ponded melt sheet. The primary morphology and size of
the Sudbury Crater remains the subject of extensive discussion. A model is
presented explaining the transformation of an originally circular crater to
the current elliptical form. Processes involved in the geometrical
transformation include; a) volume reduction through melt sheet
crystallization, and repeated expulsion of melt into the surrounding
footwall, b) translation and segmentation on multiple southeast dipping
thrust surfaces, and c) relative displacement on steep north- northwest
trending faults. Paleomagnetic, geochemical and structural evidence supports
the concept of periodic melt expulsions into the footwall. Seismic,
potential field and paleomagnetic surveys provide evidence in support of
multiple thrust surfaces. After over 9 km of subsequent erosion only a small
volumetric portion of the original SIC remains, although complete vertical
sections through the melt sheet have been preserved. None of the crater wall
has been preserved. Thus the contacts between the SIC and the footwall on
the North and South Ranges are interpreted as uplifted crater floor margins.

Addresses:
Morris WA, McMaster Univ, Sch Geog & Geol, Appl Geophys Grp, 1280 Main st W,
Hamilton, ON L8S 4M1, Canada
McMaster Univ, Sch Geog & Geol, Appl Geophys Grp, Hamilton, ON L8S 4M1,
Canada

Copyright © 2003 Institute for Scientific Information

===============
(9) AND FINALLY: NUTTY PROFESSOR: "K/T IMPACT THEORY LARGELY DRIVEN BY
AMERICAN IMAGINATION"

>From Sydney Morning Herald, 5 March 2003
http://www.smh.com.au/text/articles/2003/03/04/1046540189165.htm

By Richard Macey

As if war with Iraq, global terrorism and Australia's soaring foreign debt
are not enough, here is something else to fret about.

The tectonic plates on which the continents ride could collapse into the
Earth's interior, with catastrophic results for life, a scientist said
yesterday.

Gordon Lister, from the Australia Crustal Research Centre at Monash
University, suspects such slow-motion disasters, not collisions with
asteroids, are to blame for periodic mass extinctions, including the loss of
the dinosaurs 65 million years ago.

The drifting of tectonic plates over billions of years has reshaped the
world. The Himalayas, for example, formed when India collided with Asia.

But Professor Lister said tectonic plates could also "founder" and sink into
the "sticky, flowing rock" that makes up the Earth's interior.

"It's like a ship that's going along and sinks," he said. Over millions of
years the continents and mountains alongside the plates would tear to bits,
dramatically changing climatic patterns, inducing droughts and even
replacing tropical forests with glaciers.

Asked how quickly climate changes could trigger a mass extinction, he said:
"It could be less than one million years."

New volcanos would erupt and entire continents could be swamped by lava.
Earthquakes could stir up methane buried under the sea, creating massive
greenhouse events.

One, 55 billion years ago, released 2000 billion tonnes of methane in 1000
to 10,000 years.

Professor Lister said surveys of dust deposits created by ancient meteor
impacts showed they did not throw enough debris into the atmosphere to cause
the global winters many blame for mass extinctions.

Dust dumped over New Zealand by the central American impact said to have
killed the dinosaurs amounted to "not much more than what you would find in
your house if you didn't clean for a weekend or two.

"The [meteor] impact theory is largely driven by American imagination," said
the professor, adding, however, that a meteor could have been "the last
straw" for weakened ecosystems.

Professor Lister, who conceded his views were "highly controversial",
expects tectonic plate foundering will continue to drive climatic change and
extinctions.

"In 20 to 25 million years Java will hit Port Hedland. It will make a
mountain range along the West Australian coast. You will have good skiing."

Would humans survive the next foundering of tectonic plates? "You would have
to say, based on the records, that we have had a good innings."

Copyright 2003, Sydney Morning Herald

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