HST Observations of Comet P/Shoemaker-Levy 9 (1993e)

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Session 25 -- Solar System and Heliosphere
Oral presentation, Wednesday, January 12, 10:15-11:45, Salon VI Room (Crystal Gateway)

[25.03] HST Observations of Comet P/Shoemaker-Levy 9 (1993e)

H.A. Weaver (STScI), P.D. Feldman (JHU), M.F. A'Hearn (U. Md), C. Arpigny (U. Liege), R.A. Brown (STScI), E.F. Helin (JPL), S.M. Larson (U. Az), D.H. Levy (U. Az), B.G. Marsden (CFA), K.J. Meech (U. Hawaii), K.S. Noll (STScI), J.V. Scotti (U. Az), Z. Sekanina (JPL), C.S. Shoemaker (NAU), E.M. Shoemaker (USGS), T.E. Smith (STScI), A.D. Storrs (STScI), D.K. Yeomans (JPL), B. Zellner (CSC/STScI)

Comet P/Shoemaker-Levy 9 (1993e) was observed by the Hubble Space Telescope\/ (HST) on 1993 July 1, approximately three months after its discovery and approximately one year before its predicted impact into the atmosphere of Jupiter. Approximately 20 individual nuclei were observed in images taken with the Planetary Camera (PC). Each nucleus is surrounded by a roughly spherical coma, which is responsible for most of the light being observed from this object. After subtracting this coma contribution, we find that the 11 brightest nuclei have magnitudes in the range V$\sim 23.7-24.8$. Assuming that the geometric albedo is $\sim 0.04$ and that the phase law coefficient is 0.035 mags deg$^{-1}$, these magnitudes translate into nuclear diameters in the range $\sim 2.5-4.3$ km. If each nucleus has a density of 1 g cm$^{-3}$, the total energy deposited by the impact of these 11 nuclei into Jupiter's atmosphere next July is $\sim 4 \times 10^{30}$ ergs ($\sim 10^{8}$ Megatons TNT). This latter number should be regarded as an upper limit, since we are probably slightly underestimating the coma contribution to the nuclear magnitudes. A 16 min Faint Object Spectrograph spectrum covering the spectral region from 2223$-$3278 \AA\ was also obtained in order to search for gaseous emission from OH, a common signature of cometary activity. Only scattered solar continuum radiation was detected, and the 3$\sigma$ limit on the OH emission corresponds to an upper limit on the water production rate of $\sim 2 \times 10^{27}$ s$^{-1}$. This latter number is quite similar to the estimated water production rate for comet P/Halley at a similar heliocentric distance.

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