Comet Hartley 2: EPOXI probe flyby to yield rare close-up photos
Comet Hartley 2 will get its portrait taken on Thursday by NASA's EPOXI spacecraft. NASA will snap 6,000 high-resolution images of 103P/Hartley 2, a small comet that hangs out around Jupiter's orbit.
Five years and 2.9 billion miles after its historic encounter with comet 9P/Tempel 1, a plucky NASA spacecraft is set to fly by a second comet, 103P/Hartley 2, Thursday morning.Skip to next paragraph
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The craft's second round of dancing with the comets is designed to give scientists an unprecedented look at an object thought to carry important clues about how planets in the solar system formed some 4.5 billion years ago.
Between the advanced instruments on the craft, formerly known as Deep Impact, and its relatively close 434-mile fly-by distance, the effort will provide "the most extensive observations of a comet to date," says Tim Larson, project manager for the mission -- renamed EPOXI -- at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Only four other comets have received fleeting visitations from US spacecraft: Giacobini-Zinner, Borrelli, Wild 2, and Tempel 1.
Compared to the other four, Hartley 2 is the smallest, with a core of rocky rubble and ice only about three quarters of a mile across, versus an average of about four miles across for the others. Their more-famous sibling, Comet Halley, sports an even larger nucleus, some eight miles across.
The EPOXI team hopes to figure out what accounts for the wide range of shapes and surface features of comet nuclei when "there are no obvious differences in the processes that shape the comets," says Michael A'Hearn, a researcher from the University of Maryland at College Park and the lead scientist on the project.
Hartley 2 not only is a cometary munchkin, it's an unusually active one, says Dr. A'Hearn. For its size, it spews relatively large quantities of dust and gas as it approaches the sun.
This process sculpts the surface of the nucleus. A'Hearn and his colleagues say they hope to use images of this activity and its effects to help them distinguish between features on the nucleus that have been continuously reshaped versus those that still represent pristine patches of material from the early solar system.
A high-resolution spectrometer aboard EPOXI can then tease out information about the composition of these different kinds of materials.