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Stardust Space Capsule to Touch Down Sunday in Utah

John Roach
for National Geographic News
January 13, 2006
 
If all goes according to plan, Stardust—a space capsule carrying a cargo of comet and interstellar dust particles—will 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.

Desert Landing

The spacecraft's nearly seven-year, three-billion-mile (4.6-billion-kilometer) round-trip flight is scheduled to end before dawn on Sunday.

At about 1 a.m. ET, Stardust will release its return capsule. Four hours later the capsule will blaze into Earth's atmosphere over the Pacific Ocean traveling at 28,860 miles (44,446 kilometers) an hour.

"As we come in over the western United States, this thing will light up the night sky for a brief period of time," said NASA's Tom Duxbury at a December 21 press briefing. Duxbury is the Stardust project manager at the Jet Propulsion Laboratory in Pasadena, California.

The capsule's speed is expected to be the fastest ever obtained by a human-made object, surpassing the record set in 1969 by the returning Apollo 10 command module, which reached a comparatively poky 24,791 miles (39,897 kilometers) an hour.

When Stardust's capsule drops to approximately 105,000 feet (32,000 meters), it will deploy a small parachute to slow the speeding craft.

At about 10,000 feet (3,048 meters) the main parachute will open, allowing for a soft landing at the U.S. Air Force's Utah Test and Training Range southwest of Salt Lake City—or so NASA hopes.

Project scientists want to avoid a repeat of the hard landing of NASA's Genesis spacecraft, whose parachutes failed to open upon its return to Earth on September 8, 2004. Genesis crashed into the Utah desert.

"Parachutes are parachutes. No matter how well you do it, they will occasionally not work," said Brownlee, the mission's principal investigator, when asked if the same could happen to Stardust.

"The probability of that happening is small, but it's not zero."

Even if the capsule crash-lands, however, scientists should be able to recover some of the particles, which are encased in an "extremely hard frame," Brownlee said.

Building Blocks

The particles Stardust collected will be the first unaltered bits of this primordial matter ever studied.

In fact, comet Wild 2 only began orbiting close enough to the sun for the material to boil off the comet's surface in 1974. Then, a gravitational tug by the planet Jupiter pulled the comet's orbit from beyond Uranus to just past Mars.

As such, there hasn't been sufficient time for heat to destroy the comet's particles, which have remained since the solar system formed 4.6 billion years ago.

After the capsule lands, a canister containing the aerogel will be transported to the Johnson Space Center in Houston, Texas. There, the samples will be cataloged and sent to scientists around the world for analysis.

Scientists are particularly interested in bits of particles that are composed differently from those found in our solar system. Some such grains are believed to be older than the sun.

"We expect to find those things," Brownlee said.

"We've found things like that in meteors and interplanetary dust. The only surprise we would have is if we don't find 'stardust,'" Brownlee said, referring to particles from outside our solar system.

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