[meteorite-list] Stardust from Comet Wild 2

[Don Merchant]

NASA scientists have new mystery to solve
Some of the material brought back by Stardust probe 'kind of a shock'

Associated Press
NASA scientists have a new mystery to solve: How did materials formed by 
fire end up on the outermost reaches of the solar system, where temperatures 
are the coldest?
The materials were contained in dust samples captured when the robotic 
Stardust spacecraft flew past the comet Wild 2 in 2004. A 100-pound capsule 
tied to a parachute returned the samples to Earth in January.
The samples include minerals such as anorthite, which is made up of calcium, 
sodium, aluminum and silicate; and diopside, made of calcium magnesium and 
silicate. Such minerals only form in very high temperatures.
"That's a big surprise. People thought comets would just be cold stuff that 
formed out ... where things are very cold," said NASA curator Michael 
Zolensky. "It was kind of a shock to not just find one but several of these, 
which implies they are pretty common in the comet."
The discovery raises questions about where the materials in comets form, he 
added.
One theory is that particles from the outer reaches of the solar system 
slowly move toward the sun, where they are set ablaze and shot back out. A 
scientific model once suggested that might be a natural occurrence, but it 
wasn't accepted because materials tend to cluster in zones the farther they 
are from the sun, Zolensky said.
If the model were true, materials would mix more, the NASA scientist said.
"It raises a question of why we still see zoning in the asteroid belt. It is 
a big mystery now," Zolensky said. "It's kind of really exciting."
He said it is also possible that the comet particles could have been formed 
in another solar system and catapulted into our solar system.
To determine where the particles originated, scientists are now studying 
their isotopic makeup. About 150 scientists worldwide have been studying the 
dust since it arrived.
During the $212 million mission, the Stardust spacecraft looped around the 
sun three times to capture the interstellar and comet dust. The comet dust 
was captured in a silicone-based material contained in a tennis racket-sized 
collector mitt.
The mother ship, which has traveled nearly 3 billion miles, remains in 
permanent orbit around the sun. The next time it flies by Earth will be in 
January 2009.
Don Brownlee, a University of Washington astronomer who is the mission's 
principal scientist, said in a few weeks or months he and his colleagues 
hope to know more.
"It depends on whether the isotopic composition indicates these grains are 
from our solar system or from another star," he said. "It's a real exciting 
mystery story. So stay tuned."