(meteorobs) Excerpts from "CCNet, 58/2000 - 18 May 2000"

A fairly rich issue today!

Lew Gramer

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From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 18 May 2000
Date: Thu, 18 May 2000 13:42:30 -0400 (EDT)

CCNet, 58/2000 - 18 May 2000

     THE TIMES, 18 May 2000

    Space.com, 17 May 2000

    Ron Baalke <baalke@jpl.nasadot gov>

    Larry Klaes <lklaes@bbn.com>=20



>From THE TIMES, 18 May 2000
http://www.the-times.codot uk/news/pages/Times/frontpage.html?1986266

By Nigel Hawkes, Science Editor

A COMET that passed by unnoticed three years ago has raised new fears=20
of a catastrophic collision. Although the comet was bright enough to be =

seen even by amateur astronomers in their gardens, it has been detected =

only because of measurements made accidentally by a satellite designed=20
to observe the Sun.=20

A group of Finnish meteorologists report in Nature that an instrument=20
on the Solar and Heliospheric Observatory satellite detected radiation=20
from five comets which crossed the southern skies in 1997. Four of them =

had been seen by ground-based observers but one passed by unrecorded.=20

"Because the comet was almost constant in brightness over several=20
months, it should have been easily observable from the ground," the=20
team, led by Teemu M=E4kinen, concludes. The failure to do so =
the need for full-sky surveillance of comets".=20

In some ways comets pose a greater potential hazard than asteroids.=20
There are fewer of them likely to be on a collision course but=20
detecting them well in advance is harder because they come from deep=20
space, from almost any direction and are, on average, larger.=20

The comet that was missed was a little too dim to be seen with the=20
naked eye but would have been easily visible with a telescope or even=20

Copyright 2000, The Times Newspapers Ltd.


>From Space.com, 17 May 2000

NASA Tries to Revive Comet-Chasing Craft

By Andrew Bridges
Pasadena Bureau Chief
posted: 07:00 am ET
17 May 2000

PASADENA, Calif. - Reaching across 179 million miles (288 million=20
kilometers) of space, engineers will shortly begin beaming new software
to a NASA spacecraft in a last-ditch effort to ready the idle probe for
a 2001 rendezvous with a distant comet.

The innovative software, hastily written and tested over the past five=20
months, will allow NASA's Deep Space 1 to recast the role of its=20
science camera into that of navigational instrument. The original=20
instrument, called a star tracker, ceased functioning in November 1999.

That loss, still unexplained, left the spacecraft without a way to use=20
the stars to orient itself in space. Since then, the spacecraft has=20
remained in a near slumber.

But that slumber must end soon if Deep Space 1 is to resume its course=20
so it can pull off a bonus September 2001 flyby of the comet Borrelly.

Full story here:



>From Ron Baalke <baalke@jpl.nasadot gov>

One giant leap

An asteroid probe that can jump could leave crawlers standing
By Jeff Hecht
New Scientist Magazine
May 13, 2000

HOPPING may be the best way for robotic probes to explore the surface=20
of comets and asteroids. Japanese engineers have built a cylindrical=20
prototype that they say could take 9-metre hops in a low-gravity=20
environment. They propose adding a more advanced version of the probe=20
to MUSES-C, a Japanese mission to return an asteroid sample to Earth in =

June 2006.

Wheeled robots work well on moons and planets, but the very low gravity =
of asteroids and comets poses problems. The traction needed for=20
horizontal motion comes from the vehicle's weight pressing down on the=20
surface, but on an asteroid only 2 kilometres across the force of=20
gravity is about 100 000 times weaker than on Earth. That leaves so=20
little traction that the robot's wheels will slip unless they move very =

Full story here:



>From Larry Klaes <lklaes@bbn.com>=20


Scientists touch gems older than solar system=20

Keay Davidson=20
May 15, 2000=20

The oldest substances ever to touch human hands - microscopic gems from =
outer space - could change our understanding of the solar system and=20
the origin of its elements.=20

So tiny that they're dubbed "engagement rings for bacteria," these=20
"presolar grains" are found within larger space rocks called meteorites =
and in fluffy debris from the tails of comets.=20

The grains are called "presolar" because of their age. They might be 6=20
billion years old - more than a billion years older than the sun,=20
Earth, and other planets - according to Donald D. Clayton, the
scientist who predicted their existence a quarter of a century ago.=20

"Their very existence shattered the belief that studying objects of=20
such antiquity on Earth is impossible," yet most of the astronomers=20
remain almost unaware of the implications of such objects,
says Clayton, a professor at Clemson University in South Carolina. He=20
is a pioneering figure in study of "nucleosynthesis," the study of the=20
origin of the chemical elements.=20

The micro-gems' reality was vigorously debated in the 1970s. Then it=20
was experimentally confirmed in the late 1980s, when they were found=20
within meteorites.=20

Yet more than a decade later, most scientists seem unaware of their=20
existence - unaware that they now has access to these relics of an=20
unimaginably distant time, a time long before Earth and the rest of the
solar system formed. "The world of astronomers has been relatively=20
ignorant of this happening," says Clayton, who campaigns to boost the=20
visibility of presolar grains.=20

Examined under a microscope, some grains, which are typically=20
millionths of a meter wide, resemble macadamia nuts that have been=20
partly excavated by nibbling mites.=20

Clayton recently sent a letter to the journal Science, remarking that a =
story on trends in planetary science research neglected to stress the=20
historic relevance of presolar grains. In a response published in the=20
same issue, the article's author, planetary scientist David J.
Stevenson of Caltech, readily acknowledged the objects constitute an=20
"important, remarkable, and undisputed development."=20

Before the solar system formed=20

Presolar grains tell us "about the stars that contributed to the=20
material from which the solar system formed. . . . It is a testament to =
our origin," Stevenson explained in an e-mail to The Examiner
last week.=20

Why have astronomers been so slow to pick up on such a fundamental=20
discovery - of these calling cards, as it were, from the youth of the=20
Milky Way galaxy?=20

Clayton offered an explanation: "People are busy pursuing their own=20
(fields of) expertise - that's how you get to the top - and sometimes=20
we don't take note of other developments that are happening."=20

According to present theories, the presolar grains form from chemical=20
isotopes ejected by exploding stars and red giant stars. Over billions=20
of years, clouds of gas, molecules and presolar grains accumulate.=20
Eventually gravity pulls them together. The result is an object massive
enough to undergo nuclear fusion reactions - a star, like our Sun.=20

The rest of the cloud collapses into a rotating disk, in which matter=20
gathers into asteroid-like rocks called planetesimals. Many=20
planetesimals gradually accumulate into planets, like Earth.=20

Grains ride in meteorites, comets=20

Presolar grains aren't floating around the solar system by themselves,=20
waif-like. They travel aboard bigger chunks of matter - meteorites,
asteroids and comets.=20

For example, over the millions of years during which the cloud=20
collapsed into the sun-circling disk, the presolar particles chemically =

interacted with, and became locked within, asteroids. During collisions
between asteroids, slivers and chunks fly off.=20

Some of those slivers eventually fall to Earth as meteorites. Flying=20
many miles per second through space, some meteorites glow brilliantly=20
as they heat from friction with Earth's atmosphere. A few are
recovered and sent to scientists. They use careful chemical techniques=20
to recover tiny presolar grains from the celestial visitor.=20

"Tiny" is the operative word: A typical carbon-rich meteorite contains=20
only a minute amount of presolar grains - about one part in 100,000,=20
Clayton says.=20

Their presolar origin was determined by examining variations in the=20
numbers of isotopes within the grains. (Certain elements come in=20
slightly different forms, dubbed isotopes, that behave the same
chemically but vary in weight because they carry differing numbers of=20
electrically neutral particles called neutrons.)=20

Variations in isotopes=20

As it turns out, presolar grains display wild variations in their=20
isotopic ratios. This, Clayton says, could have only one credible=20
cause: They formed in the extremely hot atmosphere of a star or in the
hellish mega-explosion of a supernova or exploding star.=20

"As the hot gas cools, the gems can solidify before the stellar=20
isotopes become diluted with the interstellar gas," Clayton says. The=20
isotopic ratio is "the smoking gun" of the particles' deep-space,
pre-solar system origins, he adds.=20

Their age cannot be determined because they contain too few atoms for=20
analysis. But researchers are trying to think of ways to examine such=20
tiny objects that might eventually yield a precise age, he says. =20

"The solar system is 4.6 billion years old - we know that number pretty =

well," Clayton says. "All we know for sure is these particles are older =

than that."=20

Why study such substances? Because they hail from a period before the=20
solar system was born, their composition could shed light on the=20
chemical composition of the primeval cloud from which it condensed=20
billions of years ago.=20

They might also contain clues to old questions of solar system=20
formation, such as: Did the primeval cloud collapse at least partly in=20
response to a shock wave from an exploding star?=20

"The grains, as 'stardust' - pieces of stars - record details of those=20
stars' production of new elements," Clayton says. "This has shown=20
several aspects of stars that we were calculating incorrectly. So the
grains are teaching us about stars, about their internal structure,=20
about the nuclear reactions that happen within them. It's all very=20

In that regard, presolar grains are leftovers from the cosmic process=20
that made you, me and the world around us possible: nucleosynthesis.=20

In this process, extreme heat and pressure within stars and supernovae=20
fuses atomic nuclei to assemble the elements heavier than hydrogen and
helium. Those elements include the elemental building blocks of Earth - =

such as iron and silicon - plus those that make life possible: among=20
them, carbon and oxygen.=20

"The calcium in your bones and the iron in your hemoglobin in your=20
blood are atoms that were all created in pre-solar supernova=20
explosions," Clayton points out.=20

An introduction to presolar grains is on the World Wide Web at:=20

http://www.ciwdot edu/lrn/psg_main.html

=A92000 San Francisco Examiner =20

The CCNet is a scholarly electronic network. To subscribe/unsubscribe,=20
please contact the moderator Benny J Peiser <b.j.peiser@livjm.acdot uk>.=20
Information circulated on this network is for scholarly and=20
educational use only. The attached information may not be copied or=20
reproduced for any other purposes without prior permission of the=20
copyright holders. The fully indexed archive of the CCNet, from=20
February 1997 on, can be found at =
http://abob.libs.ugadot edu/bobk/cccmenu.html

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