PLEASE NOTE:
*
CCNet DIGEST, 7 December 1998
-----------------------------
(1) THE MYSTERIOUS GEMINID METEOR SHOWER
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(2) TSUNAMIS FROM ASTEROID IMPACTS
Michael Paine <mpaine@tpgi.com.au>
(3) CHINESE 'DEATH RAY' THREATENS US SATELLITES
The Sunday Times, 6 December 1998
http://www.sunday-times.co.uk:80/news/pages/Sunday-Times/frontpage.html?1617548
(4) THE END & THE BEGINNING: RECOVERIES FROM MASS EXTINCTIONS
D.H. Erwin, NATIONAL MUSEUM OF NATURAL HISTORY
(5) COSMIC IMPACT & MASS EXTINCTION AT THE K/T BOUNDARY
K.O. Pope et al.,
(6) DENNET VS GOULD
J.C. Ahouse, UNIVERSITY OF WISCONSIN
=================
(1) THE MYSTERIOUS GEMINID METEOR SHOWER
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
Marshall Space Flight Center
http://science.nasa.gov/newhome/headlines/ast04dec98_1.htm
On December 13, 1998, fragments of a curious object called 3200
Phaethon will produce a beautiful sky show
Dec. 4, 1998: 1998 was a great year for meteor watching. In
November
the much-anticipated Leonids produced an outburst of nearly 600
meteors per hour, punctuated by a spectacular display of
fireballs
seen worldwide. The October Giacobinids were also a pleasant
surprise
for many, thanks to an outburst over Japan and east Asia. As 1998
winds down, there is one more opportunity to view a dazzling sky
show: the annual Geminids meteor shower.
The shower officially begins on December 6th, but it doesn't peak
until the night of the 13th. Unlike the Giacobinids and Leonids,
the
Geminid's broad maximum lasts nearly a full day, so observers
around
the globe have a good chance to see the show. At its peak the
Geminids are expected to produce about one shooting star every 30
seconds.
Most well known meteor showers, like the Perseids and Leonids,
are
old. They've been observed for hundreds or even thousands of
years.
The earliest record of a modern-day meteor shower is probably a
notation in Chinese annals dated 36 AD, regarding the Perseids,
where
it is said that "more than 100 meteors flew thither in the
morning."
The Geminids are a different story. The first Geminid meteors
suddenly appeared in the mid-1800's. Those early showers were
unimpressive, boasting a mere 10-20 shooting stars per hour.
Since
then, however, the Geminids have grown in intensity until today
it is
one of the most spectacular annual showers. In 1996, the last
time
the Geminids appeared in a dark moon-less sky, observers saw as
many
as 110 per hour. Sky-watchers with clear skies should see at
least
that many this year if the Geminids continue to intensify.
After the discovery of the Geminids in 1862 astronomers began
searching for the parent comet. Most meteor showers result from
debris that that boils off a comet's nucleus when it passes close
to
the sun. This debris orbits the sun along with the comet, forming
a
thin, elongated stream of meteoroids that become shooting stars
when
they hit Earth's atmosphere.
Years of searching proved to no avail until finally, in 1982,
NASA's
Infrared Astronomical Satellite discovered a curious object
moving in
the same orbit as the Geminid meteoroid stream. The orbital match
was
so good that it had to be the source of the debris, but to the
surprise of many it wasn't a comet. The source of the Geminids
was
apparently a rocky asteroid.
3200 Phaethon, as the asteroid is now known, is in a highly
elliptical 1.4 year orbit that brings it within 0.2 AU
(astronomical
units) of the Sun. It made its closest recent approach to Earth
in
December 1997 when it passed within 0.31 AU of our planet.
But how does an asteroid produce a meteoroid debris stream?
Comets do
it easily whenever they pass close enough to the sun to heat
their
frozen nucleus. Tiny bits of ice and dust naturally bubble away
into
interplanetary space. Rocky asteroids are made of tougher stuff,
however, so it is unclear how bits of 3200 Phaethon would break
or
boil off to form a meteoroid stream.
One of the earliest ideas was that Phaethon might occasionally
collide with other asteroids. Collisions would create a stream of
pulverized rocks that would account for the Geminids meteor
shower.
Phaethon's orbit passes through the asteroid belt just beyond
Mars,
so at first this hypothesis seemed likely, but more detailed
studies
disagree. The orbits of individual Geminid meteoroids are not
consistent with the idea that they broke free while in the
asteroid
belt. Instead, they appear to have crumbled away when Phaethon
was
closer to the Sun. In this respect Phaethon is behaving like a
comet..
So, is Phaethon a comet or an asteroid?
There are arguments in favor of both. Phaethon's spectra look
like
those of a rocky asteroid, but its orbit is similar to that of a
comet. When Phaethon passes by the sun it doesn't develop a
cometary
tail, but bits and pieces do break off to form the Geminid
meteoroids. By studying photographic records of fireballs,
scientists
have estimated the density of the Geminid meteoroids to be
between 1
and 2 gm/cc. That's less dense than typical asteroid material (3
gm/cc), but several times denser than cometary dust flakes (0.3
gm/cc). Many astronomers now believe that Phaethon is an extinct
or
dormant comet that has accumulated a thick crust of
interplanetary
dust grains. Phaethon's thick mantle gives it the outward
appearance
of an asteroid, but underneath lies the nucleus of a comet.
The origin of the Geminids may not be fully understood until
future
space travelers pay a visit to the asteroid-comet 3200 Phaethon.
Until then we can still enjoy the sky show and savor the mystery
of
the enigmatic Geminids.
How to View the Geminids
Geminids meteors can be seen anytime after 10 p.m. local time,
when
the constellation Gemini is well above the horizon, but the best
time
to look is during the early morning hours between about 2 a.m.
and
dawn. That's when the local sky is pointing directly into the
Geminid
meteor stream.
Gemini rises about 08:00 p.m. local time at mid-latitudes in the
Northern hemisphere. The radiant of the Geminid shower is located
near Castor, one of the two bright stars in Gemini (the other
bright
star is Pollux). To find the constellation at 2:00 a.m., go
outside
and face south. Castor and Pollux will appear approximately 45
degrees above the horizon. Earlier in the evening, from 10:00
p.m.
until midnight, Gemini will be about 30 degrees above the horizon
in
the southeast.
You won't need binoculars or a telescope, the naked eye is
usually
best for seeing meteors which often streak more than 45 degrees
across the sky. The field of view of most binoculars and
telescopes
is simply too narrow for good meteor observations.
Experienced meteor observers suggest the following viewing
strategy:
Dress warmly as the mid-December nights are likely to be cold in
the
Northern hemisphere. Bring a reclining chair, or spread a thick
blanket over a flat spot of ground. Lie down and look up somewhat
toward the south. Meteors can appear in any part of the sky,
although
their trails will tend to point back toward the radiant.
========================
(2) TSUNAMIS FROM ASTEROID IMPACTS
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
I have prepared a draft web page which is intended to replace the
"Tsunami from asteroid impacts" web page. Based on the
assumptions set
out in the revised page, the risk to low-lying coastal areas is
substantially less than my original estimates (which, it turns
out, were
based on worst case scenarios) but still significantly greater
than
"inland" locations.
The URL is http://www1.tpgi.com.au/users/tps-seti/tsunami.html
Comments are most welcome.
Michael Paine mailto:mpaine@tpgi.com.au
New South Wales Coordinator, The Planetary Society Australian
Volunteers
=============
(3) CHINESE 'DEATH RAY' THREATENS US SATELLITES
From The Sunday Times, 6 December 1998
http://www.sunday-times.co.uk:80/news/pages/Sunday-Times/frontpage.html?1617548
by Matthew Campbell, Washington
IN AN intrusion on the domain of Hollywood villains bent on world
domination, China is said to have embarked on a quest for a giant
blowtorch-like weapon that can fire a laser beam hundreds of
miles into
space to destroy satellites as they orbit the earth.
A secret Pentagon report warning of what some call the
"death ray" has
alarmed the American military, whose own tests have revealed the
vulnerability of military satellites to being "fried"
in a laser
attack. Intense research is being conducted to develop ways of
protecting vital intelligence-gathering and communications
satellites
from attack.
Amid fears of a new arms race in space, America is also
experimenting
with a laser weapon capable of destroying Scud missiles in
flight. The
research would warm the heart of Ronald Reagan, the former
president
whose dreams of using lasers in space to defend America from
incoming
nuclear missiles were widely dismissed as an expensive folly.
America has already test-fired a laser at one of its own obsolete
satellites, ostensibly to gather information about its satellite
fleet's susceptibility to enemy attack. Amid secrecy reminiscent
of the
early days of nuclear weapons, it is designing even more
elaborate
anti-satellite weapons, including a spacecraft that
"captures"
satellites and drags them down into the atmosphere, where they
burn up.
Even while they profess to be trying to avoid the militarisation
of
space, other countries such as Russia are pursuing anti-satellite
weapons programmes. International treaties may prohibit the
placing of
weapons of mass destruction in space but there are no bans on
firing
lasers into the heavens.
The Pentagon report said the Chinese - as part of a plan to
modernise
their military forces and consolidate their position as the
dominant
power in Asia - were developing anti-satellite technology. They
were
being aided, it said, by scientists from the former Soviet Union
whose
own anti-satellite weapons programme has been hampered by
economic
chaos in Russia and lack of funds.
The report revealed that China was also developing so-called
"radio
frequency" weapons as part of an "electronic
warfare" arsenal designed
to inflict havoc on an enemy by interfering with communications.
In the
field of laser technology, the report said that China "may
already
possess the capability to damage, under specific conditions,
optical
sensors on satellites".
The aim, said the report, was to "develop a capability to
establish
control of space or to deny access and use of military and
commercial
space systems in times of crisis or war". Congress was
briefed about
the threat. "It is real and substantive," said Curt
Weldon, a
Republican congressman.
America fears anti-satellite weapons could be used by its enemies
to
deprive it of its key advantage in any future conflict by
disabling its
"spies in the sky". Hundreds of military satellites
orbiting the earth
provide America and its allies with tactical information about
potential enemies. They also play a crucial role in military
targeting,
communications and navigation.
According to western intelligence sources, the Chinese were
particularly impressed by the advantage satellites gave American
forces in the Gulf war in 1991 by pinpointing Iraqi troops and
equipment. Chinese military planners have expressed anxiety that
this
edge might be used against them in any Asian conflict.
It is believed the Chinese have developed their laser weapon
along the
lines of America's so-called MIRACL laser, which has been tested
at the
White Sands missile range in New Mexico.
The army spent more than $1 billion developing the laser, which
is
housed in a complex the size of a small factory. It burns
chemicals and
uses mirrors to focus a one megawatt stream of energy into a
6ft-wide
beam that acts like a giant blowtorch and can disable satellites
hundreds of miles away within seconds.
After the apparatus was test-fired at an old military satellite
in
1997, the Pentagon was extremely coy about divulging any details
about
the results. However, military sources said the satellite had
been
badly damaged.
Other techniques for disabling satellites, remnants of Reagan's
beloved
Strategic Defence Initiative - otherwise known as Star Wars - are
quietly moving off the drawing board into the hardware stage as
American military thinking increasingly envisages space as a
future
battlefield.
"We look at space as the pipeline of the 21st century,
similar to oil
in the 20th century," said Brigadier-General Alan Johnson,
director of
plans at US Space Command, explaining the military's growing
interest
in space.
American military forces depend more on satellites for
communications
and observation than those of any other country. Boris Yeltsin,
the
Russian president, has called for a moratorium on the testing of
anti-satellite weapons. But it is unlikely to be heeded - least
of
all by the Chinese as they seek to modernise their armed forces.
In America, laser technology is being promoted not just for use
against satellites: the air force is developing an airborne laser
system carried by a jumbo jet for finding and destroying Scud
missiles within seconds of their launch. Travelling at 186,000
miles
per second, a laser beam could reach out across thousands of
miles to
knock out a missile in the time it takes to travel a few feet.
Eventually lasers might be placed in satellites that could find
and
destroy missiles armed with nuclear, chemical or biological
weapons.
While some critics balk at the idea of letting laser weapons into
space, the threat posed by rogue dictators such as Iraq's Saddam
Hussein suggests that the "death ray" may be the
deterrent of the
future.
Copyright 1998, The Sunday Times
===========================
(4) THE END & THE BEGINNING: RECOVERIES FROM MASS EXTINCTIONS
D.H. Erwin: The end and the beginning: recoveries from mass
extinctions. TRENDS IN ECOLOGY & EVOLUTION, 1998, Vol.13,
No.9,
pp.344-349
NATIONAL MUSEUM OF NATURAL HISTORY, DEPT PALEOBIOL, MRC
121, WASHINGTON, DC, 20560
The evolutionary consequences of mass extinctions depend as
much on
the processes of survival and recovery following these biotic
crises
as on the patterns of extinction themselves. Paleontologists are
currently documenting biotic recoveries from six major mass
extinctions and several smaller biotic crises. Although the
immediate
responses are remarkably similar after each event, with
low-diversity
assemblages dominated by widespread, eurytopic species, the
recovery
response in the long-term is more varied. Lineages that survive
the
extinction can lack the resilience for recovery, whereas others
vanish from the fossil record seemingly to return from the dead
after
several million years. Copyright 1998, Institute for Scientific
Information Inc.
=====================
(5) COSMIC IMPACT & MASS EXTINCTION AT THE K/T BOUNDARY
K.O. Pope*), S.L. D'Hondt, C.R. Marshall: Meteorite impact and
the mass
extinction of species at the Cretaceous/Tertiary boundary.
PROCEEDINGS
OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF
AMERICA,
1998, Vol.95, No.19, pp.11028-11029
*) GEO ECO ARC RES,2222 FOOTHILL BLVD,LA CANADA
FLINTRIDGE,CA,91011
=============================
(6) DENNET VS GOULD
J.C. Ahouse: The tragedy of a priori selectionism: Dennett and
Gould on
adaptationism. BIOLOGY & PHILOSOPHY, 1998, Vol.13, No.3,
pp.359-391
UNIVERSITY OF WISCONSIN, HOWARD HUGHES MED INST,RM BOCK LABS,1525
LINDEN DR,MADISON,WI,53706
In his recent book on Darwinism, Daniel Dennett has offered up a
species of a priori selectionism that he calls algorithmic. He
used
this view to challenge a number of positions advocated by Stephen
J.
Gould. I examine his algorithmic conception, review his
unqualified
enthusiasm for the a priori selectionist position, challenge
Dennett's
main metaphors (cranes vs. skyhooks and a design space), examine
ways
in which his position has lead him to misunderstand or
misrepresent
Gould (spandrels, exaptation, punctuated equilibrium, contingency
and
disparity), and discuss recent results in developmental biology
that
suggest that an a priori position does not fill the demands of an
evolutionary biology. I conclude by insisting that evolutionary
biology
is many leveled, complicated, and is carried on an ever shifting
and
expanding empirical base that when disregarded results in
caricature.
Copyright 1998, Institute for Scientific Information Inc.
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