DOUBLE TROUBLE

Sky & Telescope News Bulletin
September 29, 2000

Among the most surprising asteroid-related discoveries of the past decade was finding the little moon Dactyl orbiting 243 Ida in 1993 and a satellite around 45 Eugenia last year. Solar-system specialists now suspect that asteroid satellites are hardly rare and may in fact be common.

The evidence to bolster this conclusion is mounting rapidly. Steven J. Ostro (Jet Propulsion Laboratory) has just announced results of radar observations, made by his team on September 22nd and 23rd, which reveal the small near-Earth asteroid 2000 DP107 to be double. "The images show separations of up to at least 1 kilometer between the components, which have different sizes and rotation states," Ostro writes in IAU Circular 7496.

In addition, ground-based astronomers have a growing list of asteroids whose light curves look like eclipsing binaries. The strongest cases involve two other small Earth-crossers, 3671 Dionysus and 1996 FG3. There is also suspicion surrounding 90 Antiope, a sizable (120-km) object in the main belt, and last year Ostro and others used radar to determine that 216 Kleopatra had a 200-km-long dog-bone shape. William F. Bottke (Southwest Research Institute), who studies the mechanic characteristics of asteroids, wonders whether big bodies like Kleopatra and Antiope can be made to spin with so much angular momentum -- via an off-center impact, for example -- that they literally fly apart. Bottke and colleague Daniel Durda hope to simulate such scenarios in the coming months.