Two billion miles is a long way to go for less than an ounce of dust.
"It's pretty exciting and, naturally, a bit nerve-racking," said Donald Brownlee, a University of Washington astronomer and principal investigator for NASA's Stardust mission, which aims to capture some comet particles on Friday.
Launched in 1999, the Stardust spacecraft was sent into orbit around the sun to rendezvous with the orbit of comet Wild 2 (pronounced "Vilt" after its Swiss discoverer), take photos and collect the first deep space samples of one of the most ancient members of our solar system -- the remnants of stellar explosions millions of years ago.
"We know almost nothing about comets," Brownlee said. "Yet they are fundamental to understanding our origins."
More precise information about what comets are made of, he said, will lead to better understanding of our planet and ourselves. Life exists on Earth largely due to the presence of water and carbon, Brownlee said, both of which were brought here by countless collisions with comets and asteroids over millions of years of planetary evolution.
"We are stardust," said Brownlee, echoing the Woodstock anthem.
The UW astronomer has dreamed of collecting stardust for decades.
In 1980, Brownlee began working on the dream with Peter Tsou at the NASA Jet Propulsion Laboratory in Pasadena, Calif. Tsou developed the world's least-dense solid -- a glass foam that is 99.9 percent air, known as aerogel -- that will be used to capture the comet dust as the craft flies by at 13,000 mph.
"The biggest risk is if we get hit by a particle that is marble-sized or large enough to damage the spacecraft," Brownlee said.
Most particles burning off the comet's coma (the cloud of emitted gas and dust at the front end of the comet, where Stardust will do the collecting) are microscopically small, he said. The risk of getting whacked by a larger particle, he said, is estimated to be no more than 2 percent.
"Still, this is space and you never know what will happen," Brownlee said. "The only surprising thing that can happen is if we don't have any surprises."
Stardust has made three orbiting loops around the sun since launch and will encounter Wild 2 more than 240 million miles away from Earth on the other side of the sun.
"We're going halfway to Jupiter to get this stuff," Brownlee noted.
A visit by Halley's Comet in the mid-1980s was the first target for Brownlee and Tsou but that mission never materialized. Wild 2 turns out to be a better choice because it is a relatively recent visitor to the inner solar system, having been deflected closer to us recently by Jupiter's gravitational pull. Unlike Halley's Comet, which has been altered as a result of orbiting the sun for a long time, Wild 2's composition is more pristine.
Looked at from a geological time scale, Brownlee said, comets and asteroids routinely whack the Earth. "Just ask the dinosaurs about that," he said.
In addition to gaining better understanding of comet composition, Brownlee said, the Stardust mission could come in handy if we ever need to deflect a killer comet or asteroid. Learning what they are made of and how to approach this comet may provide information and skills we need to prevent our extinction, he noted.
But at this point, Brownlee's main concern is for the survival of Stardust as it nears its approach to Wild 2 and prepares to fly through the comet's hail of particles traveling five times the speed of a bullet.
A tennis-racket shaped collector with the aerogel will flip up to collect the dust as the spacecraft also does some close-up photography and gas analysis.
Once the mission is completed, Stardust and Wild 2 will part ways as the spacecraft continues for another billion miles its return to Earth's orbit.
On Jan. 15, 2006, a capsule containing the aerogel collector will detach from the spacecraft, enter the atmosphere and at 2:45 a.m. (Mountain Time) parachute down on to the Utah desert southwest of Salt Lake City, where it will be collected and taken to NASA for precise analysis of the particles.
Stardust, Brownlee's brainchild, represents the first mission devoted to studying a comet and the first samples of a deep space object ever brought back to Earth.
"I'm biased but I think this is pretty impressive," said the astronomer.
For more information, see http://stardust.jpl.nasa.gov P-I reporter Tom Paulson can be reached at 206-448-8318 or tompaulson@seattlepi.com