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Plans for Voyager 2 UVS Observations



from Jay Holberg, LPL, 20 June, 1994

The Voyager 2 Ultraviolet spectrometer (UVS) will observe Jupiter during the Comet Shoemaker-Levy 9 impact events in July. The Voyager 2 UVS is sensi- tive over the 500 to 1700 A range with a spectral resolution of approximately 18 A. Voyager 2 will have a relatively direct view of the Jovian hemisphere where the impacts will occur but will be 42.4 AU from Jupiter. Observations of Jupiter will begin on July 8 and will continue through August 15. Plans call for the collection of 18 hrs per day of real-time data from Voyager 2. According to present predictions, the impacts of most fragments will occur during periods when real-time data are available. The following events, how- ever, will not be observed because they occur in gaps in scheduled ground- station coverage: D, E, K, N, P2 and S. There remains a 50% probability that event T will also occur in one of these gaps. The total light time delay is 11.6 hrs between the times of each impact and the reception of the corresponding data from Voyager 2 at Earth.

Aspects of the impacts that might be detected with the Voyager 2 UVS include the upper atmospheric bolide phases of the entry of the fragments and possible post-impact enhancements of the Io torus emission. Assuming black- body-like energy distributions for emitted flux, we calculate that the UVS would be sensitive to effective temperatures above 10,000 K with projected surface areas in excess of 10 square km that develop above the Jovian homopause. Such events would appear as stellar-like continuum sources in the spectral range 1200 to 1700 A. The basic UVS time resolution for these observations is 3.84 seconds. The above detection limit is based on this integration time. In the longer term, the UVS will remain pointed at Jupiter for approximately one month following the impacts in order to look for any dramatic brightening of the Io torus associated with the comet entry.

Investigators involved in these observations include Jay Holberg, Bill Sandel, Floyd Herbert, and Alex Dessler at the Lunar and Planetary Laboratory, University of Arizona.