4 November 2010

Comet Flyby Today!

Posted by Ryan Anderson

EPOXI flying past a comet. Image credit: NASA/JPL/UMD/Pat Rawlings

Today we get to see a new comet! Ok, so the comet is actually quite old, and we’ve known about it since 1986, but this will be the first time we see the surface. The EPOXI mission will be swinging by the comet Hartley 2 in about an hour and a half, snapping high-resolution pictures and collecting other information all the way.

If you haven’t heard of the EPOXI mission before, don’t feel bad, it has an unusual pedigree. EPOXI is the mission formerly known as Deep Impact. You know, the one that bombed comet 9P/Tempel back in 2005, making some lovely fireworks for the 4th of July? Well, once it had done its job there, NASA still had this operational spacecraft drifting around the sun so they decided to use it for something else. Two missions of opportunity were selected: one uses the cameras on Deep Impact to observe stars with planets that pass in front of them. This one, called EPOCh (Extrasolar Planet Observation and Characterization) was completed while the spacecraft was on its way to today’s comet encounter. The other extended mission, DIXI (Deep Impact Extended Investigation) is the comet encounter itself. Now, those names weren’t confusing enough, so the folks in charge decided to combine the two acronyms and call the overall extended mission EPOXI. Thanks NASA, for making everyone who wants to write about this mission have to explain your awkward naming scheme!

Anyway, EPOXI or whatever it is called is finally approaching the comet Hartley 2 today! Hartley 2 is a very active comet. In fact, according to Dr. Jessica Sunshine, an EPOXI team scientist, the comet is spewing more gas than you would expect if its entire surface were actively vaporizing into space. On most other comets that have been visited by spacecraft, only a small fraction is actually active, so it will be interesting to see what Hartley 2 looks like up close. It’s already surprising us: in September, the comet began belching out a cloud of cyanide gas. Cyanide (CN) has been seen coming from other comets, but Hartley 2 erupted with the stuff for 10 days.

I’ll post an update later today once the first pictures from the flyby are released. In the meantime, check out this cool animation of four recent EPOXI images of Hartley 2 put together by Emily Lakdawalla over at the Planetary Society blog. Emily has also posted a detailed timeline of the flyby and will be tweeting and blogging about it in case you want to follow along.

An animation of four images taken by EPOXI as it approached Hartley 2 over the last few days. Credit: NASA / JPL / UMD / animation by Emily Lakdawalla