A Piece of Interplanetary Dust
The dust that pervades our Solar System is not the dust that pervades our homes.
Solar System dust comes from comets and asteroids, whereas house dust is most likely lint or
dead cells. Pictured above is a piece of interplanetary dust caught by a high-flying U2-type
aircraft. It likely originates in the early days of our Solar System, being stored and later
ejected by a passing comet. The particle is composed of glass, carbon, and a conglomeration
of silicate mineral grains. It measures only 10 microns across, a tenth the width of a typical
human hair. NASA's STARDUST mission, launched in 1999, is scheduled to pass through the
tail of Comet Wild 2 in 2004 and return many more interstellar dust samples to Earth in 2006.