Near miss, but no threat—Asteroid in close pass was smaller than thought, astronomer shows

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http://web.mit.edu/newsoffice/2009/harmless-intruder-0316.html

Near miss, but no threat

Asteroid in close pass was smaller than thought, astronomer shows

David Chandler, MIT News Office
March 16, 2009

On March 2, an asteroid whizzed past the Earth at a distance of just 41,000 miles -- a near miss by cosmic standards (most communications satellites orbit at a distance of about 22,300 miles from Earth). Headlines around the world proclaimed that Earth had dodged a bullet, and many mentioned that if the space rock had hit our planet, it might have packed a punch comparable to the Tunguska impact in 1908 that flattened trees over an 800-square-mile area in Siberia.

But some fast-tracking observations by MIT Professor of Planetary Sciences Richard Binzel proved that this rock was actually much smaller than that. Likely just 19 meters (about 60 feet) across, it would probably have disintegrated high in the atmosphere, with only a few small fragments making it to the ground.

Discovered just two days before its closest approach to Earth, the asteroid, called 2009 DD45, was initially estimated as between 20 and 40 meters across. At the high end, that would have made it comparable to the devastating Tunguska bolide. Binzel, on sabbatical at the Paris Observatory, decided to try to make observations of the fast-moving asteroid, aided by MIT planetary science alum Francesca DeMeo '06 SM '07, who is currently completing her doctoral research in Paris on a Fulbright scholarship.

The asteroid's close pass was on the opposite side of the planet from Paris -- over the Pacific Ocean. No problem for Binzel: He and his students have routinely made observations using a remotely controlled telescope in Hawaii (See News Office story from last year: http://web.mit.edu/newsoffice/2008/asteroids-tt0319.html). The telescope can be run from a number of different locations, including a control room on the MIT campus and the Paris Observatory.

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