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(meteorobs) Excerpts from "CCNet 94/2001 - 28 August 2001"
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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 94/2001 - 28 August 2001
Date: Tue, 28 Aug 2001 11:20:45 +0100
CCNet 94/2001 - 28 August 2001
------------------------------
"During the past decade, astronomers have begun finding members of
an unusual breed of asteroids. Called Damocloids after the first of
their kind discovered, 5335 Damocles, these asteroids have elliptical
orbits that resemble those of short-period comets like Comet Halley. A
new member of this strange astronomical club has now been found, and its
brightness suggests that it might be the largest Earth-crossing asteroid
known."
Vanessa Thomas, Astronomy.com, 24 August 2001
[...]
(4) LARGE EARTH-CROSSING ASTEROID FOUND
Astronomy.com, 24 August 2001
[...]
(7) METEOR EXCITES NIGHT SKIES OVER COLORADO
Ron Baalke <baalke@jpl.nasadot gov>
[...]
(9) FROM MARS TO EARTH IN A METEORITE?
Scientific American, 24 August 2001
[...]
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(4) LARGE EARTH-CROSSING ASTEROID FOUND
>From Astronomy.com, 24 August 2001
http://www.astronomy.com/Content/Dynamic/Articles/000/000/000/585wmvek.asp
Large Earth-Crossing Asteroid Found
A newly discovered rare asteroid may be the largest Earth-crosser known.
by Vanessa Thomas
During the past decade, astronomers have begun finding members of an unusual
breed of asteroids. Called Damocloids after the first of their kind
discovered, 5335 Damocles, these asteroids have elliptical orbits that
resemble those of short-period comets like Comet Halley. A new member of
this strange astronomical club has now been found, and its brightness
suggests that it might be the largest Earth-crossing asteroid known.
Provisionally titled 2001 OG108, the object was first spotted on July 28 by
Michael Van Ness, an observer for the Lowell Observatory Near-Earth-Object
Search (LONEOS) program in Arizona. Over the next two weeks, observers
tracked the newfound asteroid to determine its path about the sun. Like
other Damocloids, 2001 OG108 has an elongated orbit. Each trip about the sun
takes it from beyond Uranus to just within Earth's orbital path.
Because Damocloids mimic the course of short-period comets, astronomers
suspect these unique asteroids might actually be "dead" comets. While the
gas and ices that cause comets to flare up when they approach the sun may
have been exhausted, the dark, rocky remains continue to travel through the
solar system. If this notion is correct, these asteroids should have the
same dark surfaces typical of short-period comet nuclei.
However, 2001 OG108 is one of the brightest Earth-crossing asteroids found
so far. According to LONEOS director Ted Bowell, just two other
Earth-crossers rival it in brightness. But 1866 Sisyphus and 2000 WF129
orbit the sun in the inner solar system and are unlikely to be as
intrinsically dark as 2001 OG108, Bowell says. If the newly discovered
asteroid is darker and reflects less light than Sisyphus and 2000 WF129, but
appears just as bright, it must be larger.
Based on its brightness, its current distance, and an expectation of its
albedo, Bowell estimates that 2001 OG108 could be as large as 10 miles (15
kilometers). The median size of the approximately 800 known Earth-crossing
asteroids is less than one kilometer, so "this object really sticks out," he
says.
Although 2001 OG108 will occasionally zip past Earth during its 50-year
journey about the sun, Bowell assures that Earthlings need not worry that
the asteroid will impact Earth - at least not in the near future. In its
present orbit, the Damocloid will not come any closer to us than about 28
million miles (about 45 million kilometers), or more than 100 times the
distance between Earth and its moon. The astronomer points out, however,
that the asteroid could potentially pass within 100 million miles of
Jupiter, which may result in an orbital adjustment by the giant planet's
gravitational manipulation.
Currently passing through the main asteroid belt toward the inner solar
system, 2001 OG108 will make its next close approach to Earth in April of
next year. As it zooms past Polaris in our northern skies, the asteroid will
be bright enough for amateur astronomers to spot with moderately sized
telescopes. Professional astronomers will likely take interest in this rare
space rock as well, in order to study its composition and attempt to confirm
its once-cometary nature.
===========================================================================
(7) METEOR EXCITES NIGHT SKIES OVER COLORADO
>From Ron Baalke <baalke@jpl.nasadot gov>
http://www.zwire.com/news/newsstory.cfm?newsid=2264796&title=Meteor%20excite
s%20night%20skies&BRD=1190&PAG=461&CATNAME=Top%20Stories&CATEGORYID=410
Meteor excites night skies
Valley Courier
August 24, 2001
SAN LUIS VALLEY - A very bright, orange-white meteor lit up skies over a
large portion of central and eastern Colorado on August 17 at 10:44 p.m.
Many people called television stations or law enforcement agencies thinking
a plane had crashed and started a forest fire.
Calls to the meteorite research team at the Denver Museum of Nature &
Science overloaded phone lines and e-mails.
The meteor was seen as far away as New Mexico, Wyoming, Idaho, Nebraska and
Kansas.
Full story here:
http://www.zwire.com/news/newsstory.cfm?newsid=2264796&title=Meteor%20excites%20night%20skies&BRD=1190&PAG=461&CATNAME=Top%20Stories&CATEGORYID=410
===========================================================================
(9) FROM MARS TO EARTH IN A METEORITE?
>From Scientific American, 24 August 2001
http://www.sciam.com/news/102700/1.html
Martian life could have reached Earth inside a meteorite, according to a new
study, which looks not at fossils or microbes but at magnetic fields. When
ALH84001 was first discovered in the Allan Hills of Antarctica in 1984, it
appeared to be just another Martian meteorite. After analyzing it more
closely, however, a team of scientists at NASA and Stanford University
declared in 1996 that it bore evidence of past life on Mars--namely, tiny
mineralized structures, which they believed to be fossilized, primitive
bacteria-like organisms. This spectacular finding didn't go unchallenged for
long, and the potato-size meteorite has been at the center of controversy
ever since.
Now ALH84001 has become the focus of a new question. A study of the famed
rock published in today's issue of Science examines whether life--if it
existed--could have traveled from Mars to Earth inside meteorites. Many
scientists have argued that thermal sterilization would prevent such a trip:
when a meteorite is ejected from Mars and later enters Earth's atmosphere,
its surface reaches several thousand degrees--temperatures hot enough to
kill any living thing. The new study, however, suggests that a meteorite's
core may stay sufficiently cool.
Researchers from the California Institute of Technology, led by Benjamin
Weiss and Joseph Kirschvink, looked at minuscule patterns of magnetization
within the rock as it was heated and cooled. As molten rock cools off, it
normally magnetizes in the direction of the local geomagnetic field, much
like a compass. In the case of ALH84001, however, the researchers found no
regular pattern of magnetization. Instead they discovered several
heterogeneous magnetic fields within the rock that were probably caused by
fractures it incurred while still on Mars. This finding is important because
it indicates that the core of the meteorite never endured the lethal
temperatures its surface felt during the interplanetary trip.
"The heat doesn't move very quickly in the meteorite," Kirschvink explained.
"As the surface of the meteorite heats up, the melting surface is blown
away, so it carries the hot material away from the meteorite." According to
Kirschvink, the extreme heat never reaches more than a few millimeters into
the rock. His group concluded from their measurements that the temperature
at ALH84001's core never exceeded 40 degrees Celsius, or about 100 degrees
Fahrenheit, en route from the Red Planet.
If heat didn't pose a threat to life, what of the voyage through space?
According to Weiss, the European Space Agency conducted tests with bacteria
to see how long they would survive in a near vacuum, exposed to subzero
temperatures and ultraviolet radiation in space. "After six years they were
still alive," Weiss said. Only one in every 10 million meteorites makes the
trip from Mars to Earth anywhere near that quickly; most spend millions of
years in space. "About a billion tons of Martian rocks have been transferred
[to Earth] throughout the history of the planet," Weiss notes. And "once
every million years there was a meteorite impact on Mars that was large
enough to free enough mass to transport life to Earth." There is no evidence
that life-forms from Mars have reached Earth, Weiss said but added: "If
there were microorganisms on Mars, then it is probable that they would have
made it here." --Harald Franzen
Copyright 2001, Scientific American
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