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NASA's Stardust spacecraft, which is on a mission to collect and return the first samples from a comet, began collecting tiny interstellar dust grains earlier this week. Interstellar dust is found throughout our galaxy in the space between the stars and yet is largely invisible in ordinary light. Only within dusty molecular clouds can it be seen where it obscures background stars. "If you look at the Milky Way on a dark night you may see a black band stretching along the center. The band is interstellar dust blocking the light from distant stars." said Dr. Don Brownlee, the principal investigator of the Stardust mission. Whilst our Solar System moves through the galaxy it moves through the tenuous clouds of interstellar dust grains. Most of these dust grains are deflected by the interplanetary magnetic field produced by the wind of charged particles streaming from the Sun, however, some penetrate to the orbit of the Earth. The dust particles are mainly smaller than one-hundredth the width of a human hair. The Stardust mission is using aerogel, the world's lightest solid, to try to capture particles as the spacecraft travels in the same direction as the dust stream until December 9, 2002.
Stardust will collect ancient interstellar dust as well as that which is passing through our Solar System today. Comets are made from interstellar dust grains that clumped together with ices 4.5 billion years ago when our Solar System formed and by collecting dust from Comet Wild 2 NASA can, therefore, sample ancient interstellar grains. "Stardust's tennis-racket-shaped particle collector has shoulder and wrist joints that will point one side of the aerogel collector material into the dust stream to collect interstellar dust," said Tom Duxbury, the project's manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "When Stardust encounters comet Wild 2 in early 2004, the reverse side of the collector will trap particles from the gas and dust escaping from the inside of the comet. When the dust samples return to Earth in 2006, we will extract and analyze the particles."
Interstellar dust grain are thought to be formed by condensation from gases streaming away from giant stars and supernovae - the explosive death throws of stars. The modern and ancient interstellar dust grains collected by Stardust will thus allow scientists to study processes in stars and within interstellar space and how these may have changed over the history of our Solar System. This is the second and final time Stardust will collect modern interstellar dust particles. When the spacecraft returns to the Earth in 2006 the dust will be made available for scientists around the world to study.
More info: Stardust Homepage
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