14 DAY TRIAL // The chemical analysis of the particles collected from the Wild 2 comet turned out a completely unexpected result: there are a number of minerals that only form at very high temperatures. But how did these minerals end up in the composition of one of the coldest bodies in the solar system?!
"Remarkably enough, we have found fire and ice," said Stardust principal investigator Don Brownlee an astronomer from the University of Washington. "In the coldest part of the solar system, we found samples that formed at extremely high temperatures. It's thought that the ices in comets formed at temperatures about 30 degrees above absolute zero, and yet we're finding minerals that formed at over 1,500 degrees."
"It was kind of a shock to not just find one but several of these [minerals], which implies they are pretty common in the comet", said NASA curator Michael Zolensky.
The minerals include a compound of calcium, sodium, aluminium and silicate called anorthite; and a compound of calcium magnesium and silicate called diopside.
Insofar, in about a month, scientists have removed and analyzed six of the 132 aerogel cells. The stardust particles were caught inside the aerogel when the spacecraft approached the comet. The spacecraft circled around the Sun three times before returning to Earth, and the "mother ship" is still on orbit. The particles are very tiny, most much smaller than a hair's width, but there are thousands of them embedded in the aerogel. 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," said Brownlee, 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."
Although only a small fraction of the minerals found in the stardust are like diopside or anorthite these raise the biggest question about the formation of the comet and implicitely about the early stages of the solar system.
"There are two major possibilities," said Brownlee. "One that they formed in the innermost, hotter-most regions of our solar system when the sun and planets were forming, and they were thrown out - all the way out to the Pluto region of the solar system. The other possibility is they were formed around other stars, in hot regions around other stars."
In case the first assumption is correct this indicates that the early solar system was a dynamic, explosive place.
"If these are really from our own sun, they've been ejected out, ballistically out, all the way across the entire solar system, and landed out there," said Zolensky. "These materials where basically on a big conveyor belt - being shot out, and then gradually drifting in, and then being shot out again."
"It's like everything else in science. You learn something about one thing, and it raises more questions somewhere else. So we can't write all the answers right now, it's just great we have new mysteries to worry about now", said Zolensky.
To determine where the particles originated, scientists are now studying their isotopic makeup. According to Brownlee the atoms of minerals from outside our solar system have a slightly different nuclear structure than those inside. Isotopes are atoms that have the same number of electrons - and thus have the same chemical properties - but a different number of neutrons inside their nucleus.
"So it's not a matter of conjecture," added Mr. Brownlee. "We have very, very, very strong clues at the atomic level that will enable us to untangle this. We can go grain by grain and say, 'This is from the solar system and this is not from the solar system.' At least that's our expectation."
