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Large Ring Observed on Jupiter

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A very large dark ring is seen surrounding the impact site which moved onto the limb at about 10:02 UT 21 July. (perhaps the L site?) The ring extended beyond the south pole, and nearly to the equator, imaged using a Bessell blue filter and CCD detector. The central impact site was also dark in this filter. Where this ring intersected Jupiter's dark band at about 20 degrees south latitude (belt? zone?) the methane image shows a bright spot. The impact site is not bright in the methane (8900 A, 300 A wide) This complex was seen to move across the face of the planet in successive images taken between 9:24 and 10:38 UT. By 12:46 poor seeing prevented seeing it. This feature was marginally visible in a narrowband sodium filter, but not in a Cousins R filter. These observations are part of the Comet Impact Network Experiment headed by Steve Larson of the University of Arizona.

Ellen Howell
Mount Stromlo Siding Spring Observatory 1m telescope

Images obtained from Lick using a high speed CCD camera system on 20 July UT confirm the reports of Howell and others from Mount Stromlo that there is a possible large dark ring surrounding the A impact site. We observed the impact sites using a variety of filters (bandwidth 100 A). In B images obtained from 04:00 to 05:00 UT (July 20), we observe a large dark arc-like structure extending from the south pole up to -20 degrees S latitude and centered on the A impact site (which was also dark in our B images). The arc has a radius of roughly 10 arcsec. The structure is also visible in our U band images but is not visible in any of our narrowband filters. There are at least two immediately obvious possible explanations for this feature: (1) it may be the visible expression of an expanding shell (or wave) of material from the A impact site: the feature is large because the A site is oldest; (2) it may be an artifact introduced by a combination of 2-arcsec seeing and the fortuitous alignment of the GRS and H impact site along an annulus concentric to the A site. In the exploder report by Howell, the bright spot in the methane filter at the intersection of the dark ring and Jupiter's dark -20 degree band is probably the GRS. Also, the impact site on the dawn limb in the Howell image is most likely the A site. Jupiter's aspect was nearly the same at 04:00 UT on July 20 and 10:00 UT on July 21.

Jim Bell, Ted Dunham, Dominique Toublanc and Bob Thompson
Lick Observatory Crossley 36-inch Observing Team, USA.

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