Members of the Spacewatch Project, which monitors the ether for possible Earth-threatening objects, found just what they were looking for, and dreading, on 19 February. A telescope on Arizona's Kitt Peak captured a bright streak of light in the night sky: an unidentified automobile-sized object motoring straight toward Earth. An analysis of its path showed that it would pass within 0.0039 astronomical units--or a scant 500,000 km--of the home planet. The Minor Planet Center (MPC) in Cambridge, Massachusetts, promptly named the interloper 2001-D47 and alerted the astronomical community, sending several international teams scampering to their telescopes.
Jon Giorgini and Lance Benner, astronomers at the Jet Propulsion Laboratory in Pasadena, California, decided to run the orbit analysis backward to figure out where the object had come from. It was not a recently arrived asteroid, they found: Rather, it had to have already made several loops around the Earth-moon system.
"At that point, we suspected it was manmade," says Benner. Jonathan McDowell, an astronomer and space history buff at the Harvard-Smithsonian Center for Astrophysics, pegged it as the WIND satellite, launched in 1994 to study the solar wind. Scientists sling WIND around the moon to place it in different orbits. "It regularly confuses the Near Earth Object people," says McDowell, "but this is the first time it ever got [an MPC] designation."
