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(meteorobs) Excerpts from "CCNet, 93/2000 - 22 September 2000"
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 22 September 2000
Date: Fri, 22 Sep 2000 11:36:24 -0400 (EDT)
CCNet, 93/2000 - 22 September 2000
----------------------------------
[...]
(3) EROS YEILDS SECRETS FROM TIME BEFORE EARTH WAS BORN=20
NASANews@hq.nasadot gov=20
(4) EROS: SO MUCH ROCK SO LITTLE GRAVITY
Ron Baalke <baalke@jpl.nasadot gov>
(5) REVEALING EROS' SECRETS, ONE BY ONE
Ron Baalke <baalke@jpl.nasadot gov>
[...]
========================================================================
(3) EROS YEILDS SECRETS FROM TIME BEFORE EARTH WAS BORN=20
>From NASANews@hq.nasadot gov=20
Donald Savage
Headquarters, Washington, DC September 21, 2000
(Phone: 202/358-1547)
Michael Buckley
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone: 240/228-7536)
Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5017)
Martha Heil
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-0850)
NOTE TO EDITORS: N00-045
ASTEROID EROS YEILDS SECRETS FROM TIME BEFORE=20
EARTH WAS BORN=20
The asteroid Eros is so ancient it could have witnessed the=20
formation of the Earth, according to findings from NASA's=20
Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft=20
published today. =20
Four scientific papers published in the September 22 issue=20
of the journal Science represent the largest one-time=20
release of scientific data about Eros since the mission=20
began. The NEAR Shoemaker spacecraft has been in orbit=20
around the primitive Manhattan-sized asteroid since last=20
February.
The four scientific teams publishing this week include the=20
NEAR X- ray Gamma-Ray Spectrometer (XGRS) team, the=20
Multispectral Imager and now-silent Near-Infrared=20
Spectrometer team, the Laser Rangefinder team and the Radio=20
Science team.
The NEAR mission is managed by the Johns Hopkins University=20
Applied Physics Laboratory (APL) in Laurel, MD, for NASA's=20
Office of Space Science.=20
The NEAR Shoemaker web site contains the latest results and=20
high-resolution images and information: http://near.jhuapldot edu
========================================================================
(4) EROS: SO MUCH ROCK SO LITTLE GRAVITY
>From Ron Baalke <baalke@jpl.nasadot gov>
News Service
Cornell University
Contact: David Brand
Office: 607-255-3651
E-Mail: deb27@cornelldot edu
HOLD FOR EMBARGO: THURSDAY, SEPT. 21, 2000, 2 P.M., EDT
Mystery of tiny asteroid Eros -- so much rock but so little=20
gravity -- detailed in Science report
ITHACA, N.Y. -- How could something so small have so much=20
debris lying around? That is the puzzle presented by=20
asteroid 433 Eros in the first major reports on the=20
composition and history of the 21-mile-long body, the solar=20
system's first asteroid to be subjected to close study.
Writing in the latest edition of the journalScience (Sept.=20
22), Joseph Veverka of Cornell University describes tiny=20
Eros as having a surface "saturated" with tiny craters=20
smaller than 1 kilometer (0.6 miles) in diameter and=20
"abundant" with rocks 30 to 100 meters (33 to 109 yards)=20
across. The craters and the boulders, says Veverka,=20
indicate many violent collisions with the asteroid over=20
time. But the gravity on Eros is so weak "that intuition=20
and calculation tell you that most of the debris produced=20
in a collision would have escaped -- but the surface is=20
full of it."
Veverka explains: "We have several possibilities. One is=20
that we simply don't understand cratering events on small=20
objects, and somehow the debris gets thrown out at very low=20
speeds. Or the ejected material ends up in the same orbit=20
as Eros, and over time the asteroid runs back into its own=20
debris and gathers it up, which is equally bizarre. We=20
simply don't understand this."
Veverka, professor of astronomy at Cornell, is the=20
principal investigator on the multi-spectral imager (MSI),=20
or camera, and the NEAR infrared spectrometer (NIS), two of=20
the five instruments on board NASA's Near Earth Asteroid=20
Rendezvous spacecraft (known as NEAR Shoemaker), which has=20
been in orbit around Eros since Feb. 14. Between that date=20
and April 1, the four teams managing the instrument=20
packages probed the elongated asteroid for its mass=20
distribution, elemental composition and topography and=20
elevation. Their four reports in Science form the most=20
detailed view yet of an asteroid. The Veverka team's=20
report, "NEAR at Eros: Imaging and Spectral Results," notes=20
rock debris, "presumably blocks of ejecta," scattered=20
across the asteroid, but not uniformly. A strong=20
concentration of blocks, the report says, occurs in the=20
complex depression west of the saddle, a 10-kilometer=20
(6-mile) depression. The distribution of blocks shows a low=20
density at high northern latitudes, but the rocks do not=20
seem to have collected in low-lying areas of the asteroid.
"What is striking about Eros," says Veverka, "is that if I=20
look at the moon in great detail, I see lots of tiny =20
craters and fewer blocks of rock. But on this object, when=20
I get down to sizes the size of a car, there are very few=20
craters and lots of boulders." And yet, he says, the=20
surface of Eros shows clear evidence of violent impacts.
The astronomer concedes that little is known about=20
collisions on small bodies with low gravity -- "we have to=20
extrapolate a lot," he says. But calculations indicate that=20
the gravity on Eros is so low that a ball thrown from the=20
surface would escape into space. "Most of the ejecta from a=20
violent collision would be traveling at a reasonable speed,=20
and you would expect it to escape. So we simply don't=20
understand why the surface is littered with so many=20
blocks," says Veverka.
The Veverka team also confirms previous reports that Eros=20
- -- an S-type asteroid, the most common classification -- is=20
a primitive relic of the emergence of the solar system from=20
a cloud of gas and dust.
"We basically know that Eros is an example of a very=20
primitive body in which nothing much has happened other=20
than formation and cratering. If you want the most pristine=20
material in the solar system that has had the least happen=20
to it, then Eros is a good example," Veverka says.
The imaging team says there is no evidence that Eros has=20
gone through an Earth-like process of heating and=20
segregation of metal from silicates to form an iron core=20
and rocky mantle. From an analysis of surface elements --=20
by measuring radiation emissions -- and measurements of the=20
gravity field, it was determined that the asteroid is=20
homogenous.
Other institutions on the MSI and NIS team are Northwestern=20
University, the Southwest Research Institute; Rensselaer=20
Polytechnic Institute, the U.S. Geological Survey, the=20
University of Hawaii, Malin Space Science Systems, the=20
University of Maryland, the Jet Propulsion Laboratory, and=20
the Applied Physics Laboratory, at Johns Hopkins=20
University, which designed and built the NEAR spacecraft=20
and manages the mission for NASA.
Other Cornell researchers on the team include Peter Thomas,=20
James Bell, Ann Harch, Maureen Bell, Brian Carcich, Beth=20
Clark, Jonathan Joseph and Colin Peterson. Steven Squyres,=20
professor of astronomy at Cornell, is an author of another=20
of the Science papers, "The Elemental Composition of=20
Asteroid 433 Eros: Results of the NEAR-Shoemaker X-ray=20
Spectrometer."
Related World Wide Web sites:
The following sites provide additional information on this=20
news release. Some might not be part of the Cornell=20
University community, and Cornell has no control over their=20
content or availability.
* Near Earth Asteroid Rendezvous
http://www.near.jhuapldot edu/
========================================================================
(5) REVEALING EROS' SECRETS, ONE BY ONE
>From Ron Baalke <baalke@jpl.nasadot gov>
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasadot gov
Contact: Martha J. Heil (818) 354-0850
FOR IMMEDIATE RELEASE September 21, 2000
REVEALING EROS' SECRETS, ONE BY ONE
Eros, the chunky asteroid named after the god of love, is=20
slowly revealing to scientists the mysteries of its size,=20
rotation and other properties.
Eros has been studied by the Near Earth Asteroid Rendezvous=20
(NEAR)-Shoemaker spacecraft since last Valentine's day when=20
a careful maneuver put the spacecraft in orbit around the=20
asteroid to determine its properties. Some of those=20
findings, such as Eros' mass and bulk density, appear in=20
the Sept. 22, 2000 edition of the journal Science in a=20
paper by principal author Dr. Don Yeomans of NASA's Jet=20
Propulsion Laboratory. Yeomans is the radio science team=20
chief for NEAR-Shoemaker. The journal also features three=20
other research reports on Eros.
Scientists have learned that Eros is most likely made of=20
rocky material with a uniform density throughout. The=20
asteroid's bulk density is similar to that of Earth's=20
crust. Like Earth, the surface of Eros is covered with a=20
layer of looser rock and soil.
Though it is about 6,700 trillion kilograms (14,700=20
trillion pounds) in mass, Eros is a fragment from the=20
breakup of a once larger asteroid. "It's a chip off a=20
larger block from millions of years ago," said Yeomans.
Eros is rotating around its shortest axis, making one=20
revolution every 5 hours and 16 minutes. As though thrown=20
in a tight spiral pass by some cosmic quarterback, Eros'=20
rotation axis appears to remain steady on its journey=20
through space. Because the asteroid is so much smaller with=20
much less gravity than Earth, it wouldn't take an Olympic=20
athlete to jump entirely off the surface into space.
Scientists were able to study Eros' rotation, mass=20
distribution and structure based on a series of=20
observations taken onboard the spacecraft. By photographing=20
the asteroid and measuring infrared light reflected from=20
it, scientists could determine its mass, detect minerals=20
and record its motion. As the craft edged into closer and=20
closer orbits around the asteroid, it took fresh data that=20
helped determine the asteroid's size, shape and mass=20
distribution. These activities were critical for navigating=20
the spacecraft in to tighter orbits about Eros so that=20
close-up images could be taken.
"If we didn't know the precise size, shape and mass=20
distribution of the asteroid ahead of time, it would not=20
have been safe to send the spacecraft to within a few=20
kilometers of the asteroid's surface," said Yeomans.
By the mission's end in February 2001, the total surface of=20
the asteroid will have been imaged and measured.
Johns Hopkins University manages the NEAR mission for NASA,=20
and JPL is performing navigation support. Bobby G.=20
Williams, also an author on the paper, is the navigation=20
team leader. For the latest images and announcements of=20
mission progress and discoveries visit the NEAR web site at
http://near.jhuapldot edu .
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