Hubble Space Telescope Observations of the Nucleus of Comet 9P/Tempel 1

✍ Scribed by P.L. Lamy; I. Toth; M.F. A'Hearn; H.A. Weaver; P.R. Weissman

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 155 KB
• Volume: 154
• Category: Article
• ISSN: 0019-1035
• DOI: 10.1006/icar.2001.6705

✦ Synopsis

The nucleus of Comet 9P/Tempel 1, the target of the Deep Impact mission, was detected during Hubble Space Telescope observations taken with the wide-field planetary camera 2 (WFPC2) on 31 December 1997 when the comet's solar phase angle was 3. • 8, its heliocentric distance was 4.48 AU, and its geocentric distance was 3.53 AU. Sixteen images were taken through the F675W filter, and all of them revealed a point-like source without any detectable coma. From these images, we derived the R magnitude of the nucleus in the Johnson-Kron-Cousins photometric system for the entire 11.5-h time span of the observations. Assuming a prolate spheroid whose spin axis lies close to the plane of the sky, the partial lightcurve indicates semi-axes a = 3.9 km and b = 2.8 km (assuming a geometric albedo of 0.04 for the R band and a phase coefficient of 0.04 mag deg -1 ) and a rotational period in the range of ∼25-33 h. The upper limit of the parameter Afρ, which characterizes the dust production rate, is 1 cm. We also derive a fractional active area at 1.78 AU of ∼ 4%.