spacetoday.net: Triple asteroid discovered

Posted: Mon, Aug 15, 2005, 7:51 AM ET (1151 GMT)
Sylvia asteroid moons illustration (ESO)

Astronomers announced last week that they have discovered the solar system's first "triple" asteroid, a large asteroid with two smaller moons. Observations of the asteroid 87 Sylvia by ESO's Very Large Telescope revealed that the large asteroid has two smaller objects orbiting it. One, named Remus, is 7 kilometers across and orbits 710 km from Sylvia; the other, Romulus, is 18 km across and orbits 1360 km away. While moons have been found orbiting several asteroids, this is the first asteroid known to have two moons. Astronomers used the moons to compute Sylvia's mass and density, finding that the asteroid has a density only 20% greater than water, suggesting that it is made primarily of water ice and rubble, with up to 60% void space.