For Immediate Release
October 5, 2010
The Johns Hopkins University Applied Physics Laboratory
Space Telescope Science Institute, Baltimore, Md.
Hubble Space Telescope observations of comet 103P/Hartley 2, taken on Sept. 25, are helping in the planning for a Nov. 4 flyby of the comet by the Deep Impact eXtended Investigation on NASA’s EPOXI mission.
Analysis of the new Hubble data shows that the nucleus has a diameter of approximately 0.93 miles (1.5 kilometers), which is consistent with previous estimates.
The comet is in a highly active state as it approaches the Sun. The Hubble data show that the coma is remarkably uniform, with no evidence for the types of outgassing jets seen from most "Jupiter Family" comets, of which Hartley 2 is a member.
Jets can be produced when the dust emanates from a few specific icy regions, while most of the surface is covered with relatively inert, meteoritic-like material. In stark contrast, the activity from Hartley 2’s nucleus appears to be more uniformly distributed over its entire surface, perhaps indicating a relatively "young" surface that hasn't yet been crusted over.
Hubble's spectrographs – the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS) – are expected to provide unique information about the comet's chemical composition that might not be obtainable any other way, including measurements by DIXI. The Hubble team is specifically searching for emissions from carbon monoxide (CO) and diatomic sulfur (S2). These molecules have been seen in other comets but have not yet been detected in 103P/Hartley 2.
103P/Hartley has an orbital period of 6.46 years. It was discovered by Malcolm Hartley in 1986 at the Schmidt Telescope Unit in Siding Spring, Australia. The comet will pass within 11 million miles of Earth (about 45 times the distance to the Moon) on Oct. 20. During that time the comet may be visible to the naked eye as a 5th magnitude "fuzzy star" in the constellation Auriga.
"I have very fond memories of comet Hartley 2, because we discovered a new emission that traces the carbon monoxide molecule when we observed this comet in September 1991," says Johns Hopkins University Applied Physics Laboratory astronomer Hal Weaver, who leads the Hubble observation team. "That was the first time a Hubble spectrograph was trained on a comet.
“The observations were technically challenging,” Weaver continues, “and we were essentially joy-sticking Hubble to keep it pointing accurately at the comet's nucleus. It was an unusual way to operate Hubble, and is not even allowed any more, but our observations of Hartley 2 were exciting and successful.”
Joining Weaver on the Hubble observation team were APL’s Neil Dello Russo; Michael A’Hearn, University of Maryland; Paul Feldman, Johns Hopkins University; and Alan Stern, Southwest Research Institute.
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.
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