for National Geographic News
If all goes according to plan, Stardusta space capsule carrying a cargo of comet and interstellar dust particleswill scream into Earth's atmosphere Sunday, deploy a series of parachutes, and drift down to the Utah desert. (Watch a video of the Stardust mission.)
Expected to land at 3:12 a.m. local time, the cargo may reveal answers to fundamental questions about comets, the origins of the solar system, and the building blocks of life.
"The samples we collected"that came out of a comet two years ago"are the same particles that went into the formation of the comet four and a half billion years ago," said Donald Brownlee, an astronomy professor at the University of Washington in Seattle.
Brownlee is the principal investigator for the NASA's Stardust mission.
The spacecraft launched February 7, 1999, to collect dust swirling off a comet and return it to Earth. Scientists believe comets are the leftover building blocks of stars and planets (interactive solar system map).
Scientists believe the particles Stardust collected from comet Wild 2 (pronounced Vilt 2) are composed of compounds, minerals, and structures that have remained unaltered for billions of years.
Looking at these particles will be somewhat like looking at an ancient book and still being able to read the words and understand the story they tell, Brownlee says.
Just past Jupiter, the spacecraft collected the particles using a tennis-racket-shaped device filled with a light, porous material called aerogel. When they hit the gel each particle was traveling at six times the speed of a bullet fired from a rifle.
Prior to the collection of the comet dust on January 2, 2004, the reverse side of the racketlike collector snared interstellar dust grains flowing into our solar system from other stars in the galaxy.
The capsule now contains tens of thousands of comet grains and about a hundred bits of interstellar dust, project coordinators say.
The spacecraft's nearly seven-year, three-billion-mile (4.6-billion-kilometer) round-trip flight is scheduled to end before dawn on Sunday.
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