Solar system's first triple asteroid system found

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Sci/Tech

The solar system's first triple asteroid system has been found, boosting predictions that such systems result from collisions between asteroids.

About 20 "binary" asteroids - composed of two asteroids orbiting one other - have been found in the main asteroid belt between Mars and Jupiter. Now, a third object has been spotted around one of these pairs, which includes one of the largest asteroids in the belt.

Called 87 Sylvia, the 280-kilometre-wide, potato-shaped asteroid lies about 3.5 times further from the Sun than the Earth does. Astronomers discovered an 18-km-wide moon orbiting it at a distance of about 1360 km in 2001. The newly found moon lies about twice as close to Sylvia, at a distance of 710 km, and measures just 7 km across.

Researchers led by Franck Marchis of the University of California in Berkeley, US, found the little moon using an infrared camera and adaptive optics on one of the four 8-metre telescopes making up the Very Large Telescope in Chile. Adaptive optics is a technique used to correct for Earth's atmospheric turbulence.

"People have been looking for multiple asteroid systems for a long time because binary asteroid systems in the main belt seem to be common," Marchis says. "I couldn't believe we'd found one."

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