Space

03/15/2006

Postcard from Outer Space

The Surprising Secrets of Comet Dust

The NASA spacecraft Stardust returned to Earth in January after seven years collecting space dust from the furthest reaches of the solar system. Scientists, this week, said the findings were unexpected.

It was February 1999 when NASA's Stardust spacecraft left Earth behind on its way to a deep-space rendezvous with a cold clump of ice and dust named Wild 2. Five years later, the comet and the spaceship played a game of space chicken the likes of which had never before been attempted -- Stardust passed within a mere 149 miles of the speeding spaceball. And then happily proceeded to eat its dust.

This week, scientists in charge of the program released the first tantalizing glimpse of the dust Stardust managed to collect. The particles have quickly become a must for anyone studying the origins of comets and those wondering what goes on at the frozen edges of our solar system where comets are thought to develop.

The findings are not quite what scientists expected. "The interesting thing is," says Donald Brownlee of the University of Washington, the lead scientist on the Stardust mission, "we are finding these high-temperature minerals in materials from the coldest place in the solar system…. Remarkably enough we have found fire and ice."

Stardust returned to Earth on January 15 this year following a seven-year mission which saw the spacecraft orbit the sun three times to collect the interstellar and comet dust. The particles -- the first extraterrestrial material brought to Earth since the manned moon mission -- were collected by a special silicone-based material called aerogel. It's a clear substance that is 99.9 percent air but looks and feels like glass reborn as Styrofoam. The particles left dozens of tracks in the aerogel as they were captured and the streaks can now be seen with the naked eye. Scientists spent hours removing the particles with a computer-controlled needle.

The specks are made up of a number of glassy materials and crystals. One mineral collected, called olivine, can be found all over the universe including in the famous green sand seen on some Hawaiian beaches. Scientists are hoping to be able to determine where these particles originates. The results may provide a hint of where comets come from.

But Stardust holds still more secrets. One more aerogel panel from the craft remains to be examined. Images from it will be posted on NASA's Web site later this month.

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