Astronomers from the US and France have discovered an asteroid with two small moons. The asteroid, 87 Sylvia, has been known since 1866, and known to have a single moon since 2001; the second moon was a complete surprise. The discovery was made using the European Southern Observatory's 8.2m Very Large Telescope in Chile while astronomers were trying to pin down motions of the first moon. These moons allowed astronomers to estimate the mass of 87 Sylvia, and they found it was only 20% higher than water. It's probably a loose pile of rubble held together by gravity, with mostly empty space.