Five days after being discovered, an interplanetary visitor whizzes past

By Camille M. Carlisle

Web edition: June 27, 2011

A shudder of air and a quick streak of light were the only signs of an asteroid’s near-Earth flyby on June 27. Asteroid 2011 MD isn’t this year’s closest approach by a near-Earth object, nor is it the largest (a 400-meter-wide boulder is expected to pass within the moon’s orbit in November). What got the Internet buzzing was that 2011 MD was discovered only five days before its flyby.

Frankly, there’s enough space junk out there that a five-day lead time is pretty good: a 2008 asteroid that actually exploded over Sudan was ID-ed less than 24 hours before it littered debris across the Nubian desert. This time around, the last-minute RSVP only whizzed past, zipping a safe 12,300 kilometers (about 7,640 miles) above South Atlantic at about 1 p.m. EDT. That’s below geosynchronous satellites but still far above satellites in polar orbit (850 km) and the International Space Station (400 km).

The asteroid is somewhere between 5 and 20 meters across, and around the length of a school bus. Observers from the MIT-based Lincoln Near Earth Asteroid Research (LINEAR) program found 2011 MD on June 2 with one of the two New Mexico telescopes that it uses to track near-Earth traffic. LINEAR has already spotted 39 near-Earth asteroids this year. Combined with other searches, LINEAR’s discoveries puts this year’s roundup at 460, according to NASA’s Near Earth Object Program.

Though it wasn’t much to see,  at least one telescope did snap a shot of 2011 MD as it flew over Australia. And there might have been a faint streak in South Africa’s twilit skies.

Though the near miss was of little note on Earth, it may have been a pretty big deal on 2011 MD.  Earth’s gravity could have set the rock shaking in an asteroid quake, throwing off dust to reveal  a less weathered layer below. Examining that layer could give observers clues about the object’s composition. And the asteroid’s  orbit — which is similar to Earth’s — will veer, too, how much so depending on the space rock’s mass. Not to fear: The out-of-whack trajectory isn’t expected to bring 2011 MD slamming into us in the future.