Asteroid That Hurtled Past Earth Has a Miniature Moon

Asteroid 2004 BL86 safely flew past Earth on Jan. 26, 2015.
Asteroid 2004 BL86 safely flew past Earth on Jan. 26, 2015. NASA/JPL-Caltech

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An asteroid that hurtled past Earth at a distance of 745,000 miles on Monday brought along a surprise — a small moon that scientists detected orbiting the larger space rock.

Scientists using NASA’s Deep Space Network antenna at Goldstone, California, grabbed a glimpse of asteroid 2004 BL86 during its relatively close flyby, which was still at a distance three times that of Earth’s moon. The images showed a tiny moon measuring about 230 feet across, circling the 1,100-foot-wide asteroid.

"This is an object that's rounded. It has a moon," NASA research scientist Lance Benner said during a webcast on Monday. The moon was actually discovered days before by Joseph Pollock of Appalachian State University and Petr Pravec of the Ondrejov Observatory near Prague, Benner said.

"Using radar last night we confirmed their observations," Benner said. "We can clearly see two objects."

Monday’s flyby was the closest this particular asteroid will come to Earth for another 200 years. On this run, scientists gained more information about the asteroid’s orbit and where it might show up in the future, as well as whether it might have boulders on its surface.

The next big space rock slated to zoom so close to Earth is asteroid 1999 AN210, due in 2027.


— Matthew DeLuca and Alan Boyle