The Deep Impact probe (now on a mission called EPOXI) passed by comet Hartley 2 at 7:01 a.m. PDT, the fifth time in history that a spacecraft has been close enough to photograph the heart of a comet. The probe flew through the comet’s diffuse corona at about 27,500 miles per hour and came within 435 miles of its icy, dirty core.
Observations leading up to the flyby showed that Hartley 2 is small but active. It’s only about 1.36 miles across, a shrimp compared to other comets that have been visited by spacecraft. But it spews several times more gas and dust than other comets. In this image from the moment of closest approach, the comet looks like a bowling pin or a peanut, with at least two jets streaming off toward the sun.
“It’s hyperactive, small and feisty,” said Don Yeomans, a senior research scientist at NASA’s Jet Propulsion Lab.
Deep Impact locked its instruments and began taking pictures of the comet 18 hours before nearest approach, when it was 496,000 miles away. By the time of closest approach, it was snapping photos once every four seconds.
But astronomers had to wait almost an hour after closest approach to get the good shots. The close-ups were stored on the spacecraft because Deep Impact couldn’t point its antenna toward Earth and its cameras toward the comet at the same time.
Hartley 2’s jets of material act as little rocket thrusters, making the comet’s orbit hard to pin down.
Read more at Wired
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