Magazine article Science News

Comet Sampler: Fire Meets Ice

Magazine article Science News

Comet Sampler: Fire Meets Ice

Article excerpt

The first study of comet dust brought to Earth by a spacecraft has revealed several minerals that could have formed only at the fiery temperatures close to the sun or another star. The findings come as a surprise because comets, frozen relics of the early solar system, were born beyond the orbit of Neptune and spend most of their time there.

Don Brownlee of the University of Washington in Seattle and his colleagues base their findings on the first particles they've examined from the Stardust craft, which sped within 236 kilometers of the nucleus of Comet Wild 2 in 2004 and collected material expelled by the frozen body. In January, a canister of the samples parachuted to a Utah desert (SN: 1/21/06, p. 37).

The scientists have sliced a few of the micrometer-size grains into hundreds of samples. The grains include the green silicate crystal olivine as well as minerals rich in titanium and aluminum. Olivine forms at temperatures from 900 to 1,100 kelvins, while the other minerals require a temperature of about 1,400 K.

The results suggest that Wild 2 and perhaps other comets are amalgams of some of the hottest and coldest materials in the solar system, Brownlee said last week at the annual Lunar and Planetary Science Conference in Houston.

Two leading theories may account for the high-temperature materials in the comet, he notes. According to one scenario, the particles formed in the inner solar system when the sun, now 4.6 billion years old, was less than 10 million years of age. …

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