The Coma of Comet 9P/Tempel 1 |
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Authors: | C M Lisse M F A’Hearn T L Farnham O Groussin K J Meech U Fink D G Schleicher |
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Institution: | (1) Planetary Exploration Group, Space Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD, 20723, U.S.A.;(2) Department of Astronomy, University of Maryland, College Park, MD, 20742, U.S.A.;(3) Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI, 96822, U.S.A.;(4) Department of Planetary Sciences, University of Arizona, LPL, Tucson, AZ, 85721, U.S.A.;(5) Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ, 86001, U.S.A. |
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Abstract: | As comet 9P/Tempel 1 approaches the Sun in 2004–2005, a temporary atmosphere, or “coma,” will form, composed of molecules
and dust expelled from the nucleus as its component icy volatiles sublimate. Driven mainly by water ice sublimation at surface
temperatures T > 200 K, this coma is a gravitationally unbound atmosphere in free adiabatic expansion. Near the nucleus (≤ 102 km), it is in collisional equilibrium, at larger distances (≥104 km) it is in free molecular flow. Ultimately the coma components are swept into the comet’s plasma and dust tails or simply
dissipate into interplanetary space. Clues to the nature of the cometary nucleus are contained in the chemistry and physics
of the coma, as well as with its variability with time, orbital position, and heliocentric distance.
The DI instrument payload includes CCD cameras with broadband filters covering the optical spectrum, allowing for sensitive
measurement of dust in the comet’s coma, and a number of narrowband filters for studying the spatial distribution of several
gas species. DI also carries the first near-infrared spectrometer to a comet flyby since the VEGA mission to Halley in 1986.
This spectrograph will allow detection of gas emission lines from the coma in unprecedented detail. Here we discuss the current
state of understanding of the 9P/Tempel 1 coma, our expectations for the measurements DI will obtain, and the predicted hazards
that the coma presents for the spacecraft.
An erratum to this article is available at . |
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Keywords: | comets coma dust gas composition jets 9P/Tempel 1 Deep Impact |
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