AAT Image of Fragment A & C Impacts

AAT IRIS Observations of the Impact Sites of Comet Shoemaker Levy-9
Fragments A and C on Jupiter

Dave Crisp, Vikki Meadows, Stuart Lumsden and Steve Lee

We are using the Infrared Imaging Spectrometer (IRIS) on the 3.9m Anglo-Australian Telescope (AAT) at the Siding Spring Observatory near Coonabarabran, Australia to observe the collisions of the fragmented comet Shoemaker Levy-9 (SL9) with Jupiter.

IRIS is a near-infrared camera/spectrometer with a 128 by 128 HgCdTe (NICMOS II) detector. This instrument can be used for direct imaging at wavelengths between 0.9 and 2.5 micron, or for acquiring spatially-resolved near-infrared spectra. With the K-grism, this instrument can be used in drift-scanning mode to construct images with a spatial resolution of 0.6 arc-seconds/picture-element at 128 simultaneous wavelengths between 2.0 and 2.4 microns. This mode was used to monitor the impact sites of fragments A and C on 17 July, 1994.

The nine images shown here were constructed by averaging images taken at wavelengths between 2.33 and 2.4 microns. These data were collected between 6:10 UT and 10:49 UT. North is up and east (on Jupiter) is to the right. The first panel shows the planet Jupiter as it normally appears at these wavelengths. Strong absorption by methane gas in the Jovian atmosphere darkens the majority of the planet's disk, with the exception of the north and south polar regions, which are shrouded by bright, high-altitude aerosols. The second panel, which was taken at 6:45 UT, shows the impact site of Fragment A. This fragment struck Jupiter about 10 hours earlier (one Jupiter rotation period). The size of this feature is larger than the Earth's moon. A second bright feature, associated with the impact of fragment C was first detected at about 7:13 UT. Panel 3 shows this feature on the morning limb, just to the south-west of the fragment A impact site. The fragment C impact site was initially much brighter than that of fragment A, but its brightness decayed somewhat as it moved onto the day side of Jupiter. The apparent separation of these two impact sites increased as they rotated into view,. Panels 4-9 show the positions and relative brightness of the A and C sites at 7:29, 8:05, 8:53, 9:07, 9:35, and 10:49 UT.

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