[meteorite-list] Comet from Coldest Spot in Solar System has Material from Hottest Places (Stardust)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Mar 14 10:31:06 2006
Message-ID: <200603140137.k2E1btU21285_at_zagami.jpl.nasa.gov>

Office of News and Information
University of Washington
Seattle, Washington

CONTACT:
Vince Stricherz, 206-543-2580

Mar. 13, 2006

Comet from coldest spot in solar system has material from hottest places

Scientists analyzing recent samples of comet dust have discovered minerals
that formed near the sun or other stars. That means materials from the
innermost part of the solar system could have traveled to the outer
reaches, where comets formed.

"The interesting thing is we are finding these high-temperature minerals
in materials from the coldest place in the solar system," said Donald
Brownlee, a University of Washington astronomer who is principal
investigator, or lead scientist, for NASA's Stardust mission.

Among the finds in material brought back by Stardust is olivine, a mineral
that is the primary component of the green sand found on some Hawaiian
beaches. It is among the most common minerals in the universe, but finding
it in comet Wild 2 could challenge a common view of how such crystalline
materials form.

Olivine is a compound of iron, magnesium and other elements, in which the
iron-magnesium mixture ranges from being nearly all iron to nearly all
magnesium. The Stardust sample is primarily magnesium.

Many astronomers believe olivine crystals form from glass when it is
heated close to stars, Brownlee said. One puzzle is why such crystals came
from Wild 2, a comet that formed beyond the orbit of Neptune when the
solar system began some 4.6 billion years ago.

"It's certain such materials never formed inside this icy, cold body,"
Brownlee said.

The comet traveled the frigid environs of deep space until 1974, when a
close encounter with Jupiter brought it to the inner solar system. Besides
olivine, the dust from Wild 2 also contains exotic, high-temperature
minerals rich in calcium, aluminum and titanium.

"I would say these materials came from the inner, warmest parts of the
solar system or from hot regions around other stars," Brownlee said.

"The issue of the origin of these crystalline silicates still must be
resolved. With our advanced tools, we can examine the crystal structure,
the trace element composition and the isotope composition, so I expect we
will determine the origin and history of these materials that we recovered
from Wild 2."

Brownlee is among scientists presenting the first concrete findings from
the Stardust sample this week at the annual Lunar and Planetary Science
Conference in League City, Texas.

Stardust's captured dust from comet Wild 2 in January 2004, and the
sample-return capsule parachuted to the Utah desert on Jan. 15 to complete
the seven-year mission. The samples from Wild 2 were taken to the National
Aeronautics and Space Administration's Johnson Space Center in Houston,
and from there they have been sent to about 150 scientists around the
world, who are using a variety of techniques to determine the properties
of the comet grains.

The grains are very tiny, most much smaller than a hair's width. But there
appear to be thousands of them embedded in the unique glassy substance
called aerogel that was used to snare the particles propelled from the
body of the comet. A grain of 10 microns -- one-hundredth of a millimeter
-- can be sliced into hundreds of samples for scientists to study.

"It's not much, but still it's so much that we're almost overwhelmed,"
Brownlee said, noting that his lab has only worked on two particles so
far. "The first grain we worked on, we haven't even cut into the main part
of the particle yet."

The material, which came from the very outer edges of the solar system,
has been preserved since the start of the solar system in the deep freeze
of space 50 times farther away from the sun than Earth is. Brownlee
believes the material will provide key information about how the solar
system was formed.

"A fundamental question is how much of the comet material came from
outside the solar system and how much of it came from the solar nebula,
from which the planets were formed," he said. "We should be able to answer
that question eventually."

Besides the UW, other major partners for the $212 million Stardust project
are NASA's Jet Propulsion Laboratory, Lockheed Martin Space Systems, The
Boeing Co., Germany's Max-Planck Institute for Extraterrestrial Physics,
NASA Ames Research Center, the University of Chicago, The Open University
in England and Johnson Space Center.

###

For more information, contact Brownlee at (818) 726-5563, (206) 543-8575.

Stardust on the Internet,
     http://www.nasa.gov/stardust

IMAGE CAPTIONS:

[Image 1:
http://www.uwnews.org/photos.asp?articleID=23093&spid=23095]
This particle, a type of olivine called forsterite, was brought to Earth
in the Stardust sample-return capsule. The grain, encased in melted
aerogel, is about 2-millionths of a meter across. University of Washington

[Image 2:
http://www.uwnews.org/photos.asp?articleID=23093&spid=23097]
This image shows the tracks left by two comet particles after they
impacted the Stardust spacecraft's comet dust collector. The collector is
made up of a low-density glass material called aerogel. Scientists have
begun extracting comet particles from these and other similar
tadpole-shaped tracks. University of Washington

[Image 3:
http://www.uwnews.org/photos.asp?articleID=23093&spid=23096]
A 'keystone' cut of aerogel showing a comet particle and track. University
of California/NASA
Received on Mon 13 Mar 2006 08:37:55 PM PST