WASHINGTON - A sample of comet dust, collected by a robotic space probe with what looks a bit like a big tennis racket, is scheduled to parachute down to Earth next month, NASA scientists said on Wednesday.
The spaceship Stardust is coming to the end of its seven-year, 2.9 billion mile (4.8 billion km) round-trip mission to fly by comet Wild 2, catching dust that could give astronomers clues about how the planets formed some 4.5 billion years ago.
The ship will remain in space but a 101-pound (46 kilogram) capsule loaded with dust culled from the comet is expected to land at the US Air Force Utah Test and Training Range at 5:12 a.m. EST (1012 GMT), or 3:12 a.m. local time on Jan. 15, 2006.
If the night is clear, the Stardust capsule's descent should be visible from northern California to Oregon, scientists said at a briefing at NASA headquarters.
"This comet formed at very edge of the solar system ... out by Pluto ... and spent all its lifetime out there until recently it came into the inner part of the solar system, where we could sample it," said Don Brownlee, the principal investigator on the project.
Stardust went halfway to Jupiter to get close to Wild 2, catching hundreds of comet dust particles in a collector that looks something like a large tennis racket with a round metal ice cube tray where the strings would be.
Inside the collector's ice-cube-size compartments is a material called aerogel, a low-density substance that is 99.9 percent air, which acted to capture grains of dust emitted by the comet.
Stardust's collector got within 147 miles (236 km) of Wild 2, close enough to be bombarded by millions of cometary particles, and to catch hundreds of them.
Comets are thought to be the remnants of planet formation, made up of cosmic dust and ice. Comet collisions may have helped seed Earth with water, a prerequisite for life.
NASA officials stressed the Stardust capsule is extremely rugged and said they have prepared for the possibility of a hard landing so the samples will not be damaged before they can be studied.
A previous NASA probe called Genesis crashed to Earth in 2004 when its parachute failed to open. That craft had been on a three-year mission to collect solar ions, which were recovered by scientists even though the spacecraft was destroyed.
Story by Deborah Zabarenko
REUTERS NEWS SERVICE
