The coma of comet 9P/Tempel 1

C. M. Lisse, M. F. A'Hearn, T. L. Farnham, O. Groussin, K. J. Meech, U. Fink, D. G. Schleicher

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)161-192
Number of pages32
JournalSpace Science Reviews
Issue number1-2
StatePublished - Jun 2005


  • 9P/Tempel 1
  • Coma
  • Comets
  • Composition
  • Deep Impact
  • Dust
  • Gas
  • Jets

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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