37th DPS Meeting, 4-9 September 2005
Session 43 Deep Impact A
Poster, Wednesday, September 7, 2005, 6:00-7:15pm, Music Foyer

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[43.14] Large Secular Variations and Other Results from Narrowband Photometry of Deep Impact's Target Comet 9P/Tempel 1

D. G. Schleicher (Lowell Obs.)

We present results from multi-apparition narrowband photometry of Deep Impact target Comet 9P/Tempel 1. An on-going observational campaign was begun in March to characterize the gas and dust production as a function of orbital position, and to provide detailed measurements of the impactor's fireball and the amount of new gas and dust released into the coma following impact. As of the end of June, a total of 10 nights of observations have been obtained at Lowell Observatory this apparition while an additional 12 nights were obtained during the 1983 and 1994 apparitions. The combined 1983 and 1994 measurements showed evidence that peak gas and dust production occured about 2 months prior to perihelion, although there was only a small amount of temporal overlap in these 2 data sets. While the peak production in 2005 also clearly occurs well before perihelion, unexpectedly a large overall decrease in production rates has taken place, with water at only about 40% of the 1983 values, CN at about 50%, and dust, based on the proxy A(\theta)f\rho, at about 70%. Peak production in 2005 occured approximately 5-6 weeks prior to perihelion, and in retrospect it is evident that the limited number of 1994 measurements are intermediate to the 1983 and 2005 results, and that the time of peak production is unchanged over the past 22 years. This strongly implies that the secular decrease is not due to a change in pole orientation, but must rather be caused by a major depletion or covering up of volatiles from the primary source region(s) on the nucleus. This is likely the largest and most rapid secular decrease ever detected for a comet which has not broken apart. A(\theta)f\rho exhibited a large trend with aperture size early in the apparition -- much steeper than the canonical 1/\rho -- but very little trend by late June, possibly implying a change in dust properties with season. Based on our OH measurements, we predict a water production rate of ~5\times1027 mol s-1 at the time of impact. This research is supported by NASA's Planetary Astronomy Program.

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Bulletin of the American Astronomical Society, 37 #3
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