It was the closest flyby of a celestial body ever performed: At 12:46 a.m. Eastern Daylight Time, NASA's Deep Space 1 successfully zipped past asteroid Braille at a distance of some 10 or 15 kilometers. But it almost certainly didn't take the closeup pictures of the rock that astronomers had been waiting for. For as-yet-unknown reasons, Deep Space 1's camera was aimed the wrong way at the crucial moment.
The last images of the asteroid were taken some 70 minutes before the flyby, says John Watson, a spokesperson for NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. And although JPL is still receiving data from the spacecraft, there is little hope that they will contain any images. "It looks very pessimistic," says Watson.
Deep Space 1, launched in October 1998, is the first mission in NASA's New Millennium Program, set up to test new space technologies. It boasts a xenon-fueled ion propulsion system, high-efficiency solar cells, and an automated navigation system, AutoNav, that enables it to find its way in interplanetary space by tracking stars and asteroids, without help from ground controllers.
The asteroid it skirted today was discovered in 1992 and was only recently named after the Frenchman Louis Braille (1809-1852), who invented the alphabet for the blind. It orbits the sun in an elongated path outside Earth's orbit and has a diameter of less than 5 kilometers. Although scientific observations are seen as a mere bonus in the New Millennium Program, astronomers were hoping that detailed images of Braille's surface might enable them to deduce the shape, size, and density of the asteroid. A plasma wave spectrometer that is also aboard functioned normally today, says Watson. It will shed light on the interaction of Braille with electrically charged particles in the solar wind.
Even if the camera had been aimed the right way, the images wouldn't have been anything more than "snapshots," says JPL's Don Yeomans, because of the spacecraft's speed with respect to the asteroid, a dazzling 15.5 kilometers per second. Yeomans was on the team that analyzed the images of asteroid Eros, taken last December by NASA's Near-Earth Asteroid Rendezvous (NEAR) spacecraft. In February 2000, NEAR will start orbiting Eros, and it may eventually land on the asteroid's surface. Had it not been for a misfiring rocket, NEAR would have snuggled up to EROS last February, long before Deep Space 1's flyby.