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

[Ron Baalke]

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