Secular light curve of Comet 9P/Tempel 1

• Published in: Icarus (New York, N.Y. 1962) Vol. 191; no. 2; pp. 567 - 572
• Main Author: Ferrin, I
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 2007
• Subjects: Comets; composition; dynamics; origin; Comets
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2006.07.032

In support of the Deep Impact Mission, we have updated the secular light curve of 9P/Tempel 1 presented in Paper I [Ferrín, I., 2005. Icarus 178, 493–516], with new data sets. The secular light curves (SLC) of the comet are presented in the log and time plots (Figs. 1 and 2) and provide a clear profile of the overall shape of the envelope. We arrive at the following conclusions: (1) Improved values of 18 photometric parameters are derived including the turn on and turn off points, R ON = − 3.47 ± 0.05  AU , R OFF = + 4.20 ± 0.05  AU , and T ON = − 410 ± 25  d , T OFF = + 555 ± 25  d . (2) The improved SLC shows a most interesting and peculiar shape, with a linear power law of slope n = 7.7 ± 0.1 from R ON = − 3.47  AU to R BP = − 2.08 ± 0.05  AU , and then converts to a law with curvature. The break point of the power law at R BP = − 2.08  AU , m V ( 1 , R ) = 14.0 ± 0.1  mag , is interpreted as a change in sublimating something more volatile than water ice (most probably CO 2), to water ice sublimation. In other words, the comet's sublimation is controlled by two different substances. (3) The photometric-age (defined in Paper I) and the time-age of the comet [Ferrín, I., 2006. Icarus. In press] are recomputed, and results in a value P-AGE = 21 ± 2 and T-AGE = 11 ± 2 comet years. Thus 9P is a young comet. (4) The comet is active almost up to aphelion since the turn off point has been determined at R OFF = + 4.20 ± 0.05  AU while aphelion takes place at Q = + 4.74  AU . (5) The comet exhibits activity post-aphelion which is not understood. Two hypothesis are advanced to explain this behavior.