This image shows orbital tracks for Alexhelios and Cleoselene, the two tiny moons that circle the bone-shaped asteroid Kleopatra.
By John Roach
Kleopatra, a dog-bone shaped asteroid named after the last pharaoh of ancient Egypt, is a pile of rubble that spawned twin moons about 100 million years ago, astronomers announced in a new study.
The discovery stems from detailed observations of 135-mile-long Kleopatra with the Keck II telescope in Hawaii made in 2008 that confirmed the asteroid's dog-bone shape and the presence of two moons, each about 5 miles wide.
The scientists charted the orbits of the moons to determine the asteroid's mass. This combined with other data on the asteroid's size and shape allowed them to determine its density: a low 3.6 grams per cubic centimeter.
"That implies that somehow this asteroid has a large portion of void in its interior," Franck Marchis, an assistant research astronomer with the University of California at Berkeley, told me today. Article here