PLEASE NOTE:


*

CCNet DIGEST, 11 November 1998: LEONIDS SPECIAL
===============================================

(1) GODDARD SPACECRAFT PREPARED FOR ENCOUNTER WITH LEONID METEOR STORM
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(2) RESEARCH AIRCRAFT FLY BELOW LEONID METEOR STORM
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(3) LEONID METEOR SHOWER PROSPECTS FOR UK & EUROPE
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(4) MIR COSMONAUTS DEPLOY 'METEORITE TRAP' DURING SPACEWALK
    CNN <http://cnn.com/TECH/space/9811/11/mir.01.ap/index.html>

(5) THE DAY THE EARTH NEARLY DIED - MONDAY AUG 10 1998
    Jonathan TATE <fr77@dial.pipex.com>

(6) DUST EMISSION FROM COMET SWIFT-TUTTLE
    J. Sarmecanic et al., UNIVERSITY OF CALIFORNIA SAN DIEGO

(7) THE MATHEMATICS OF MASS EXTINCTION
    S. Chiba, SHIZUOKA UNIVERSITY

(8) NEW BOOK ON IMPACT CRATERING
    Harald Stehlik <harald.stehlik@sea.ericsson.se>

====================
(1) GODDARD SPACECRAFT PREPARED FOR ENCOUNTER WITH LEONID METEOR STORM

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

Mark Hess/Jim Sahli
Goddard Space Flight Center Nov. 9, 1998
Greenbelt, MD 20771
(Phone: 301-286-8955)

RELEASE NO: 98-184

GODDARD SPACECRAFT PREPARED FOR ENCOUNTER WITH LEONID METEOR STORM

Flight controllers are laying plans to prepare an orbiting fleet of 22
Goddard spacecraft for the upcoming Leonid meteor storm, predicted to
be the fiercest in more than three decades.

The annual Leonid shower -- this year a storm -- is expected to be
unusually intense because the Earth is crossing Comet Tempel-Tuttle's
orbital path at a time when the comet has recently passed by. This
happens once every 33 years when Tempel-Tuttle makes its closest
approach to the Sun. The Sun's radiation boils bits of dust and sand
off the comet, littering its path with debris.

Where possible, controllers will change the orientation of satellites
to reduce the possibility that one of these tiny particles (1 to 100
microns in size, or about the size of a small sand grain) will strike
and disable a spacecraft. However, Leonid storms pose a greater than
usual threat to spacecraft not only because of the many tiny meteors
(thousands per hour) hitting our atmosphere, but also the tremendous
velocities of the particles.

As the Earth moves across the comet's trail, Leonid particles will
enter the planet's atmosphere. Like two freight trains hurtling at one
another on the same track, the distance between the massive debris
cloud and the Earth closes at a mind-boggling 45 miles per second, or
over 200 times the speed of sound. In contrast, Perseid meteors reach
speeds of about 37 miles per second, and typical daily meteors achieve
velocities of about 12 miles per second.

On spacecraft where it is practicable, high voltage systems that
supply instruments will be turned off, or ramped down, to safeguard
against the potential for electrical damage as a result of the
satellite's plunge into the debris cloud. The tiny meteors can hit the
spacecraft like a sandblaster and disintegrate, creating a cloud of
electrically charged plasma. Under the right conditions, this plasma
cloud can set off a chain reaction causing a massive short circuit.
The loss of the European Space Agency's Olympus communications
satellite in 1993 was attributed to a strike from the Perseid shower,
and the resulting plasma discharge that zapped the spacecraft's
delicate electronics.

The 22 NASA spacecraft under Goddard's control -- from the 24,500
pound Hubble Space Telescope to the 25-year old, 800 pound IMP-8
satellite -- will be continuously monitored during the peak of the
storm, and some maneuvered to provide the greatest protection possible
from debris.

"Each individual mission and project team reviewed its procedure for
dealing with this annual phenomena, and has a specific implementation
plan for the Leonid meteor storm," said Philip E. Liebrecht, Associate
Director for Networks and Mission Services. "Each spacecraft has an
operating plan that balances the risk of taking specific defensive
measures against the risk of taking no action. We've had independent
review teams assess our plans, and I think we are doing everything
prudent and practicable to ensure the safety of our spacecraft."

The Leonid meteor shower arrives every November. It takes its name
from the constellation Leo, the area of the sky where the meteors
appear to originate. The shower's small particles are completely
vaporized high in the Earth's atmosphere, and present no danger to the
Earth's surface or to aircraft.

Historically, the most active Leonid showers occur during the first
two years following the comet's closest approach to the Sun. This last
occurred on Feb. 28, 1998. This year's outburst is projected to be
less severe than that observed in the last 33-year cycle, which
occurred in 1966. The peak time for the Leonid meteor storm will be
Nov. 17, sometime between 11:43 a.m and 5:43 p.m. Eastern Standard
Time.

For the past several weeks, engineers at Goddard have been reviewing
the status of all the spacecraft under their control and developing
ways to reduce exposure to the meteor storm. In general, the health of
these spacecraft will be monitored before, during and after the storm,
and commands to a number of the spacecraft will be stopped or
curtailed during this period.

The Hubble Space Telescope will be maneuvered so that its mirrors face
away from the storm. Its solar arrays will be rotated so only the
edges are exposed to oncoming particles. Controllers won't turn Hubble
off during the storm, but rather use the 10-hour period that Hubble is
maintained in this attitude to take a long-exposure picture (for more
on this, check out http://www.stsci.edu/ftp/proposer/leonid.html).

Some spacecraft, like the Tropical Rainfall Measuring Mission, are
already in the ideal orientation for the storm, and only an adjustment
to position the solar arrays "edge on" to the storm will be needed.
The Rossi X-ray Timing Explorer's instruments will be turned off to
protect the spacecraft's high voltage devices from a potential massive
short circuit similar to what happened to Olympus.

For the Advanced Composition Explorer, the solar arrays will be
rotated, and high voltage supplies for instruments will be ramped
down. Since the center of the Leonid stream is closer to the L-1 orbit
(1 million miles from the Earth toward the Sun) than to Earth, ACE
will see an even more intense storm than Earth-orbiting satellites.

Risk reduction procedures will be followed for other spacecraft
including the Extreme Ultraviolet Explorer, Compton Gamma Ray
Observatory, Upper Atmosphere Research Satellite, Total Ozone Mapping
Spectrometer, Fast Auroral Snapshot, Solar Anomalous Magnetospheric
Particle Explorer, Transition Region and Coronal Explorer, WIND,
POLAR, Solar and Heliospheric Observatory, Interplanetary Monitoring
Platform and Earth Radiation Budget Satellite.

The Tracking and Data Relay Satellites will be maintained in their
full operational mode, as these spacecraft are vital to provide the
communications link to and from other spacecraft during the peak storm
period.

Flight control teams for all of Goddard's operational spacecraft have
been briefed on the meteor storm and have developed contingency plans
to react to any damage sustained during the storm. In addition, all
available command and control capabilities will be on alert for
possible use in an emergency, and subsystem engineers will be on
standby for consultation if there are any problems resulting from the
storm.

More information on the Leonid meteor storm can be found at these web sites:

   http://www.aero.org/leonid/index.html

   http://www-space.arc.nasa.gov/~leonid/

   http://leroy.cc.uregina.ca/~astro/Leonids/Leo_1.html

===================
(2) RESEARCH AIRCRAFT FLY BELOW LEONID METEOR STORM

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

NOTE: The "Once-in-a-Century" claim in the release needs to be
clarified.

*****

National Science Foundation
Washington, D.C.

Media contact:   Cheryl Dybas, NSF           (703) 306-1070 cdybas@nsf.gov
Media contact:   Anatta, UCAR Communications (303) 497-8604 anatta@ucar.edu
Program contact: Cliff Jacobs, NSF           (703) 306-1521 cjacobs@nsf.gov

NSF PR 98-74 November 6, 1998

Research Aircraft Fly Below Once-in-a-Century Leonid Meteor Storm

Two research aircraft carrying new scientific observing instruments
and high-definition TV cameras will seize a once-in-a-lifetime
opportunity to observe the Leonids meteor shower on November 17, 1998.
Only once a century does Earth's orbit cross the dense part of the
tail of Comet Temple-Tuttle, which produces the storm.

An L-188C Electra, owned by the National Science Foundation (NSF) and
operated by the National Center for Atmospheric Research (NCAR) in
Boulder, Colo. will be joined by an Air Force KC-135 in the night
skies over Okinawa, Japan, during the meteor storm.

"The NSF Electra is an ideal platform to participate in the Leonids
meteor experiment," says Cliff Jacobs, program manager in NSF's
division of atmospheric sciences, which funds NCAR. "Its ability to
accommodate multiple state-of-the-art, upward-looking instruments will
provide an exceptional opportunity to study these meteors."

The meteor storm will occur when Earth enters the dense debris behind
Temple-Tuttle on November 17, 1998, and again on November 18, 1999.
Although the comet returns every 33 years, its orbit crosses Earth's
only once every hundred years. This century's crossing offers
scientists a close look at the trails of unusually fresh and large
(millimeter- to centimeter-size) meteors entering the earth's
atmosphere at the fastest possible speeds -- 72 kilometers per second
(160,000 miles per hour). Best observations will be from East Asia
(China and Japan). Next year, Europe and North Africa will offer the
best viewing. From the ground, the source of the storm appears in
the constellation Leo.

The National Aeronautics and Space Administration is heading the
experiment, which is the first mission in NASA's Astrobiology Program,
created to study the origin and prevalence of life in the universe.
The Leonid Multi-Instrument Aircraft Campaign is also supported by
NSF, the U.S. Air Force, and NHK Japanese television.

The two aircraft are needed to take the observing instruments into
clear skies above the weather-laden lower atmosphere. The Air Force's
FISTA (Flying Infrared Signatures Technology Aircraft) will circle the
NSF/NCAR Electra in a racetrack pattern between 30,000 and 40,000 feet
while the Electra flies back and forth (north-south) about 10,000 feet
lower within the loop. At these altitudes (7 to 10 kilometers, or
roughly 4 to 6 miles) both planes will be safe from the meteors above,
which will burn up at 100 to 120 kilometers (60 to 75 miles) above the
ground.

A major scientific goal of the mission is to determine how a meteor's
mass compares to its brightness. To date, scientists can only guess
how much material enters the atmosphere during a meteor shower. The
Electra will carry a dual-beam lidar (laser-based radar) built this
year to detect iron vaporized from the meteors in the upper
atmosphere. Says NCAR project manager Bruce Morley, "We know very
little about iron in the atmosphere and even less about the iron
contribution from meteors. Observing just one meteor accurately from
the sky would make a big difference to our understanding."

                                    -NSF-

Editors: High-resolution color photos of the Electra are available via
the Internet using anonymous ftp: Log on to ftp.ucar.edu, using the
userid: anonymous password: [your e-mail address] directory:
/communications [include the slash] filenames: elecnight1.tif,
elecnight2.tif, elecnight3.tif, elecnight4.tif, and electra.tif

================
(3) LEONID METEOR SHOWER PROSPECTS FOR UK & EUROPE

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

Royal Astronomical Society

For immediate release: 10 November 1998

Ref. PN 98/23

Issued by:

Dr Jacqueline Mitton
RAS Public Relations Officer
Office & home phone: Cambridge ((0)1223) 564914
Mobile phone: 0370 386133
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@dial.pipex.com

and

Peter Bond
Space Science Advisor
Phone: (0)1483-268672
Fax: (0)1483-274047
E-mail: 100604.1111@compuserve.com

Leonid Meteor Shower Prospects for UK and Europe

Professional and amateur skywatchers worldwide are awaiting the night
of 17th/18th November with considerable anticipation because of the
possibility that a spectacular meteor shower will take place. But what
can we really expect to see in the UK and rest of Europe?

According to the best data available, Europe is likely to experience a
good meteor shower, but not a truly exceptional one -- perhaps up to
100 meteors per hour if we are lucky. The best time to look will be
between 1 a.m. and dawn in the early hours of 18th November. A storm
of many thousands of meteors per hour could occur, but it is much more
likely to be seen in the Far East -- China, Thailand, Japan -- than in
Europe.

Forecasting Metoer Showers

Predictions of a meteor storm in 1998 are based on the fact that
exceptional displays of the Leonid meteors -- so-called because they
appear to radiate from a point in the sky within the constellation Leo
-- tend to recur every 33 years or so. There is not always a great
storm, however, such as the one in 1966 when observers in parts of the
USA for a short time saw meteors at a rate of 40 per second.

But forecasting meteor showers is not a precise business, unlike
predicting eclipses, for example, for which the exact times and
circumstances can be calculated in advance. The time when a meteor
shower will peak, and the maximum rate at which meteors will appear to
rain down, can never be anticipated with great certainty. They are
something of a celestial lottery.

For that reason, it is well worth looking out for meteors in the early
hours of the 18th, if skies are clear, even from the UK. There is a
slim chance of something exceptional, but a modest display at least is
on the cards, and meteors are easy to observe. They are best seen with
the naked eye and, during a shower, they can streak across almost any
part of the sky, as long as the radiant point is above the horizon.

If a Leonid storm takes place, it is unlikely to last more than an
hour or so, but the gentler background shower carries on for a day or
two. According to the experts the expected peak time of any storm is
most likely to be about 7.45 p.m. (GMT). If this is correct, the storm
would be finished several hours before the constellation Leo rises
above the horizon in the UK.

What Are Meteors?

Meteors are caused by small fragments of material, mostly no larger
than a grain of sand, which burn up as they enter Earth's atmosphere
at high speed -- around 71 kilometres (45 miles) per second in the
case of the Leonids.

Leonid meteors are dust particles that have come off Comet
Tempel-Tuttle. Most of this dust is still following the comet fairly
closely in space. The comet takes 33 years to complete an orbit around
the Sun, and planet Earth ploughs through its main dust cloud when the
comet returns to our vicinity every 33 years. In the years when this
happens, a strong shower or storm takes place. In the years in
between, a very small number of Leonid meteors are seen in
mid-November.

Some meteor showers produce about the same rate of meteors around the
same date every year. Regular annual showers happen when the dust from
a comet has spread around the whole of the comet's orbit, something
that takes place gradually over a long period of time. An example is
the Orionids, a shower in late October each year caused by dust from
Halley's Comet.

Looking ahead to 1999, Comet Tempel-Tuttle will still be relatively
nearby and some astronomers are predicting that the Leonid meteor
display could be better next year than this. If that were to happen,
then Europe is expected to be the ideal location.

Do The Leonids Present Any Hazards?

Most of the Leonids weigh about 1 millionth of a gram -- not much more
than a particle of cigarette smoke. Normally, objects this size would
pose no threat to spacecraft. However, when they are travelling many
times faster than a bullet from a high velocity rifle, the threat
increases significantly.

Since the velocity of the meteor impacts is affected by a spacecraft's
motion as it orbits the Earth, hits could occur at any speed between
65 and 80 km (40 and 50 miles) per second. These could result in some
physical damage in sensitive areas as well as electrical short
circuits, plasma discharges, and computer malfunctions, which may be
sufficiently serious to disable a satellite. A form of sand-blasting
can erode outer surfaces such as thermal blankets, mirrors and solar
cells. Large impacting particles may even knock a satellite out of its
normal position, as happened to the European Space Agency's Giotto
spacecraft during its 1986 flyby of Halley's Comet.

"These microparticles could penetrate a fairly weak spacecraft skin,"
said Professor Tony McDonnell of the Unit for Space Sciences and
Astrophysics at the University of Kent in Canterbury. However, the
most likely form of damage is to vulnerable power systems. "Perhaps a
handful of satellites could have unusual electrical anomalies," said
McDonnell.

Past evidence suggests that the risks are fairly low. During the past
four decades, only one spacecraft, the European Space Agency's Olympus
satellite, is known to have been disabled by a (Perseid) meteor.
Furthermore, no spacecraft were damaged by the 1966 Leonid storm. On
the other hand, there are now more than 500 spacecraft orbiting the
Earth, over 10 times as many as in the mid-1960s.

"The biggest uncertainty is the hourly rate (of arrival)," said
Professor McDonnell. "If this reaches 150,000 per hour, there will be
all sorts of damage, but there may only be 1,800 per hour."

While the probability of any satellite being hit is thought to be less
than 0.1%, many spacecraft operators are taking no chances. The Space
Shuttle mission that carried John Glenn was deliberately timed to
avoid the Leonid shower. Cosmonauts on the Mir space station do not
have the luxury of choosing their flight window. While the Mir station
presents a large target for the Leonids, no serious damage is
expected. However, the two crewmen may play safe by moving into the
Soyuz lifeboat at the peak of the shower.

Fortunately, the direction from which the particles approach the Earth
is almost perpendicular to the direction of the Sun. This means that
the chance of a direct hit will be substantially reduced since most
satellites will already have their solar panels aligned edge-on to the
shower.

Further damage-limitation measures have been recommended by the
European Space Operations Centre operated by the European Space
Agency. These include turning spacecraft so that their most vulnerable
systems are not in the direct line of fire; switching off high voltage
systems; and putting a team of ground controllers on alert in case of
emergencies.

In the case of the Hubble Space Telescope, its all-important mirror
will be turned away from the shower during observations of distant
galaxies. Most of the scientific instruments on the European ERS-1 and
ERS-2 Earth observation satellites and the Solar and Heliospheric
Observatory (SOHO) will be powered down and placed in 'sleep' mode
during the shower. SOHO and the American Advanced Composition Explorer
(ACE), which are located 1.5 million km sunward of the Earth, will be
particularly at risk since the main stream of meteors is expected to
pass much closer to them than any of their Earth-orbiting brethren.
Indeed, the trail of Leonids will actually travel between the Earth
and these two solar observatories.

More Information about the Leonid Meteors may be found at the
following Web Sites:

     Leonid '98 Meteor Outburst Mission Homepage (P. Jenniskens - NASA)
     http://www-space.arc.nasa.gov/~leonid/1998.html

     Leonid Information for the Beginning and Advanced Meteor Enthusiast
     (G. Kronk)
     http://medicine.wustl.edu/~kronkg/leonids.html

     SKY Online's Meteor Page (Sky & Telescope magazine)
     http://www.skypub.com/sights/meteors/meteors.html

Visual Material

Sky & Telescope magazine (based in Boston, USA) has available for
distribution:

   * still images from the 1966 Leonid storm,
   * artistic renderings
   * video of the 1997 Perseid and Geminid meteor showers
   * a broadcast-quality, 1-minute animation of why the Leonids occur by
     artist Don Davis.

Anyone wanting these for reproduction or broadcast can contact Irene
Szewczuk (irenes@skypub.com, phone 00 1 617-864-7360 x127) or Kelly
Beatty (kbeatty@skypub.com, phone 00 1 617-864-7360 x148). Fax for
both is 00 1 617-576-0336.

=============
(4) MIR COSMONAUTS DEPLOY 'METEORITE TRAP' DURING SPACEWALK

From CNN <http://cnn.com/TECH/space/9811/11/mir.01.ap/index.html>

November 11, 1998

MOSCOW (AP) -- Two Russian cosmonauts on the Mir space station
successfully deployed a French-made device for catching and studying 
small meteorite particles during a six-hour spacewalk that ended early
Wednesday.

Cosmonauts Gennady Padalka and Sergei Avdeyev installed the "meteorite
trap," which should collect data on a barrage of particles expected to
peak around the Mir in mid-November, said Valery Lyndin, spokesman for
mission control.

The device will stay attached to the Mir until 1999, when it will be
taken back to Earth for analysis by a French astronaut who will fly to
the station early next year.

The "meteorite rain" doesn't pose a serious threat to the Mir because 
it consists of tiny remnants, not full meteorites. To be safe,
however, the two cosmonauts will board the Soyuz escape capsule when
the shower reaches its peak.

At the start of the spacewalk, Padalka and Avdeyev released a
satellite model made by schoolchildren from several countries. [...]

Copyright 1998   The Associated Press

===================
(5) THE DAY THE EARTH NEARLY DIED - MONDAY AUG 10 1998

From Jonathan TATE <fr77@dial.pipex.com>

Benny, I thought that some might be interested in the latest from
the dubious end of the British press!

Jay

--------

From the Sunday People, 8 Nov 98

By Nigel Nelson

DAY THE EARTH NEARLY DIED - MONDAY AUG 10 1998

World was 6 hours from Armageddon

At midnight on Monday, August 10 this year the world came just SIX
HOURS from being obliterated as a giant asteroid hurtled towards us
at 50,000 miles per hour.

The Sunday People can today reveal that a MILE-WIDE space rock
missed us by just one million miles.

In cosmic terms it was a second away from being hit by a juggernaut.

If it hadn’t veered in a slightly different direction it would have:

KILLED a quarter of the population.

DESTROYED all animals and crops after blotting out the Sun.

CREATED a tidal wave an astonishing 17 miles high – Concorde only
reaches 10 miles.

DEVASTATED just about everything for 2,000 miles around.

The asteroid – the speed of which was the equivalent of travelling
from London to New York in 21 seconds – would have made the rest of
the world appear like the aftermath of a global nuclear war.

Only people with access to underground nuclear bunkers would have
had any chance of survival.  The asteroid is the biggest in recorded
history to have come so close to the Earth – a chilling echo of the
Hollywood sci-fi blockbuster movie Armageddon in which Bruce Willis
saves the world.

The cataclysmic near miss was only known to a select group of
scientists. This is why the terrifying information has never been
made public until now.

It only came to light through research by amateur astronomer and
Liberal Democrat MP Lembit Opik.

He is calling on the Government to spend 9.5 million on a giant
telescope which would track objects from space which are on a
collision with Earth.

Mr. Opik, MP for Montgomeryshire, is also campaigning for a network of
telescopes around the world to monitor objects heading towards us.

He said: “Once every 100,000 years something big hits the Earth and once
every hundred years a 50-metre object does – causing an explosion 5,000
times that of the Hiroshima bomb.

“We live in the roulette wheel of the cosmos – never knowing when a
big one might hit us.”

The asteroid was first spotted by astronomers in New Mexico on June 24.

They flashed a warning to observatories world-wide, including the
one in Armagh, Northern Ireland, which tracks objects that might hit
Earth.

It was the Irish astronomers who worked out that the asteroid would
miss us by six hours.

Armagh astronomer Dr John Chambers said: “It would have gone
straight through the ocean and hit the rock underneath throwing up
not just a gigantic tidal wave but a huge amount of dust.”

But he added, “While we were safe from this one there could well be
another on the way.”

The next asteroid scientists know about is the ten-mile wide
Toutatis – due to come within 13 hours of Earth on September 29,
2004.

===================
(6) DUST EMISSION FROM COMET SWIFT-TUTTLE

J. Sarmecanic*), M. Fomenkova, B. Jones: Modeling of mid-infrared dust
emission from P/Swift-Tuttle. PLANETARY AND SPACE SCIENCE, 1998,
Vol.46, No.8, pp.859-863

*) UNIVERSITY OF CALIFORNIA SAN DIEGO,CTR ASTROPHYS & SPACE SCI
0424,LA JOLLA,CA,92093

Comet P/Swift-Tuttle was observed at 11.7 mu m on 12 nights over the
course of three weeks in November 1992 using the UCSD mid-infrared
imaging camera (Fomenkova et nl., 1995). The large number of images
obtained and the overall high quality of the data permit the continued
study of the rich dust structures apparent in this active comet. We
present a model to interpret the features observed in these images
using olivine spheres (MgFeSiO4) as representative dust grains, and
illustrate the validity of the model by applying it to the image taken
on UT 9. 1 November. A fully three-dimensional Monte Carlo simulation
based on :the Finson-Probstein model (1968) is performed, and Mie
scattering theory is used to characterize the properties of the
grains. We found that the comet executes simple rotation about an axis
whose obliquity is 45 +/- 10 degrees. Our best-fit dust grain size
distribution in the size range from 0.6 to 10.0 mu m is of the form
f(a) similar to a(-beta) with beta = 2.5 +/- 0.5, not quite as steep
as the distribution (beta = 3.7) measured for comet P/Halley
(McDonnell er al., 1991). (C) 1998 Elsevier Science Ltd. All rights
reserved.

==================
(7) THE MATHEMATICS OF MASS EXTINCTION

S. Chiba: A mathematical model for long-term patterns of
evolution: effects of environmental stability and instability on
macroevolutionary patterns and mass extinctions. PALEOBIOLOGY,
1998, Vol.24, No.3, pp.336-348

SHIZUOKA UNIVERSITY, INST BIOL & EARTH SCI,836 OYA, SHIZUOKA 422,
JAPAN

A simple mathematical model to examine the relationships between
environmental instability and long-term macroevolutionary trends
is presented. The model investigates the evolutionary changes that
occur in certain population characters in an environment with
physical disturbance. These quantitative genetic characters are
related to intrinsic growth rates and mean carrying capacity. The
model assumes that individual fitness is determined by these
characters. I examine the likelihood of extinction under different
degrees of environmental instability and for rapid change of
environmental instability. The model suggests that characters that
promote a high intrinsic growth rate and a low carrying capacity
tend to evolve in the most unstable environments. This suggests
that small body size, high fecundity, and simple forms evolve in
unstable environments. The extinction probability of a population
is the lowest for taxa possessing K-selected characters in the
most stable environment. However, the extinction probability of a
species (metapopulation) becomes lowest for r-selected species
living in the most unstable environment and for the K-selected
species living in the most stable environment, and it becomes the
highest for taxa living in a moderately unstable environment.
Increasing environmental instability changes the extinction
probabilities of different taxa in different ways, due to
differences in phenotypes and environments. The effect of
environmental change is most serious for the K-selected taxa in
the most stable environment. This also suggests that a
continuously stable environment increases the extinction
probability of taxa when environmental change occurs. Although
catastrophic changes in environments are not presumed, these
results are consistent with the existence of two
''macroevolutionary regimes'' in which a taxon's extinction rate
and its characters differ for mass extinction and normal
extinction. Mass extinction can occur as a result of long-term
adaptation to a stable environment following a minor change of
environment without catastrophes. Copyright 1998, Institute for
Scientific Information Inc.

==================
(8) NEW BOOK ON IMPACT CRATERING

From Harald Stehlik <harald.stehlik@sea.ericsson.se>

For all GERMAN readers !

just found that there is a brand new book on impact cratering out !

It is written by Dr. Christian Koeberl, a leading researcher in
impact craters.

The title is :

IMPAKT - Gefahr aus dem All
192 pages, 13 x 21 cm
26 pictures and tables etc.
ISBN: 3-85167-074-4
The cost is DM 41.- / SFR 38.- / approx. $26.-


Harald

WIEN
AUSTRIA

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