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 ½ 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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