Solar system's first triple asteroid system found
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."