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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.


Copyright 2000 Sky Publishing Corporation. S&T's Weekly News Bulletin and Sky at a Glance stargazing calendar are provided as a service to the astronomical community by the editors of SKY & TELESCOPE magazine. Widespread electronic distribution is encouraged as long as these paragraphs are included. But the text of the bulletin and calendar may not be published in any other form without permission from Sky Publishing (contact permissions@skypub.com or phone 617-864-7360). Updates of astronomical news, including active links to related Internet resources, are available via SKY & TELESCOPE's site on the World Wide Web at http://www.skypub.com/.

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