Cosmic Paparazzi: Asteroids Caught With Mates

Robert Roy Britt

PureInsight | January 2, 2001

Once thought to be total cosmic loners, asteroids recently have been spotted in more sociable arrangements, harboring small companions. And now, as seen in newly released images, a pair of chunky twins are caught waltzing through space in a manner never before seen.

In a discovery that rocks what we know about asteroids, sort of, two hunks of stone and iron known collectively as 90 Antiope are spied against a black backdrop, circling each other every 16.5 hours while simultaneously zooming around the Sun in the outer reaches of the main Asteroid Belt, between Mars and Jupiter.

In another dazzling example of cosmic paparazzi, made possible with the latest in ground-based telescope technology, Asteroid 762 Pulcova has been spotted with a wee little companion, becoming only the third known asteroid to have what scientists call a moonlet.

Antiope (in Greek mythology a Theban princess who was seduced by Zeus and bore him twin sons) presents the more exciting configuration. Twin asteroids have never been seen before (Asteroid 216 Kleopatra was thought to be a twin but turns out to be a single, bone-shaped object). A decade ago, it could barely have been imagined, since nary a moon had yet been spotted circling a space rock.

The Antiope twins are about 50 miles (80 kilometers) in diameter each, and they're separated by about twice that amount. Because they are of similar mass, they orbit around an imaginary point in space that is roughly halfway between the two objects. Each orbital measure in their celestial dalliance takes about 16.5 hours.

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