Sunday, November 7, 2010

Comet Hartley 2 and EPOXI

Yes, I know this is old news. I'm a slow blogger, okay?

Anyway, chances are that two years ago, you heard of the Deep Impact mission. NASA sent up a small impactor and a larger space probe, and then smacked the impactor into comet 9P/Tempel (Tempel 1) at a combined closing speed of around 14 kilometers (9 miles) per second. The impact was the equivalent of five metric tons of dynamite, and produced a huge bright dust cloud. NASA got a huge amount of information out of the mission, huge success. And, oh yeah, they got pretty pictures too:


But wait. There's still a fully functional space probe up there, and it's got cameras and spectrometers, and plenty of fuel. It's time to science!

The University of Maryland joined in the project. They initially intend to fly it near comet 85P/Boethin, but it didn't return periodically as expected, and has probably broken up. So, they put the spacecraft on a holding pattern near Earth, and used it for other stuff. They used the telescopic cameras to scan for extrasolar planets, and the spectrometer to confirm observations of water molecules on the moon.

Then, in May, they had the craft, now titled EPOXI, fire its engines for 11.3 seconds, enough to change its velocity by around 3 inches per second. That was just enough that its July flyby of Earth, instead of continuing its holding pattern, flung it off into the black. Right into the path of comet 103/P Hartley (Hartley 2). It passed just 435 miles from the nucleus, revealing incredible sights:


Yep, it's a peanut, as was suspected from ground-based radar observations. The waist is smooth, but the two balls are rough, with craters and boulders, and a huge groove.

It's the fifth comet to be visited by a spacecraft; the next flyby will be when the Stardust spacecraft (which collected samples from comet Wild 2 in 2006) visits Tempel 1 in 2011.

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