"Hot" Rocks Found in Icy Comet

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Michael Zolensky is Stardust curator and a co-investigator at Johnson Space Center. He explained that our solar system is broken up into several zones.

The system includes regions where minerals form in high heat, near the sun, and areas where they form in coldness, on the fringes out by Pluto.

Finding such hot materials in a comet born so far out in the solar system is a surprise.

"It suggests that, 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," he said.

Stardust Collection

The Stardust spacecraft collected the samples using a tennis-racket-shaped device filled with cubes of a light, porous material called aerogel. The gel is 99.8 percent air and can trap delicate dust particles without damaging them.

Once the capsule was recovered from the Utah desert, scientists shipped it to Johnson Space Center. There, six of the aerogel cubes were sliced up and sent to about 150 researchers around the world.

Most of the particles are smaller than the width of a hair. Thousands are embedded in the aerogel.

Among the minerals returned to Earth is olivine—"probably one of the more common minerals in the universe," Brownlee said.

For example, it is the primary component of green sand found on some Hawaiian beaches. Scientists believe olivine forms in great heat close to stars, Brownlee added.

The samples also include high-temperature minerals rich in calcium, aluminum, and titanium.

The question facing scientists is why these minerals were part of Wild 2, a comet that formed beyond the orbit of Neptune when our solar system began taking shape some 4.6 billion years ago.

"When these minerals formed they were either red-hot or white-hot grains, and yet we collected them at a comet [from] the Siberia of the solar system, out by the orbit of Pluto," Brownlee said.

Further analysis over the coming months and years may yield answers to the new questions the findings raise about comet formation.

"We can't give you all the answers right now. It's just great we have new mysteries to worry about now," Zolensky said.

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