Asteroid that flew past Earth has its own moon

Radar images of the large asteroid 2004 BL86 as it flew past the Earth today have revealed that it has its own small moon.

The new images also show a second object positioned close to 2004 BL86. Benner told that the second object is a moon, with a diameter between 164 and 328 feet (50 and 100 m). Previous studies of the light around 2004 BL86 had already identified a moon orbiting the asteroid, and the new images confirm that discovery, he added. About 17 percent of asteroids in 2004 BL86’s size range have smaller objects trailing along with them.

Boulders and other small-scale features on the surface of the asteroid are coming into focus in the new images, as is the overall shape of the asteroid, according to Benner. He compared the object to another asteroid that made a close flyby of Earth six years ago, called 2008 EV5. It appears that 2004 BL86, like 2008 EV5, has an equatorial ridge around its middle, which makes it look “kind of like a muffin, or perhaps a top,” said Benner, who’s based at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.

This data is from radar data collected early in the fly-by, so we should expect even more details to come out in the next day or so.