31st Annual Meeting of the DPS, October 1999
Session 44. Rings II
Contributed Oral Parallel Session, Thursday, October 14, 1999, 10:30am-12:00noon, Sala Kursaal

## [44.02] The Orbit of Prometheus at the Voyager Epochs

M.W. Evans, C.D. Murray (Queen Mary and Westfield College, London), C.C. Porco (LPL/University of Arizona)

Following the 1995 Saturn ring plane crossing it was found that the satellite Prometheus was lagging behind its predicted orbital longitude by ~ 19 degrees (Nicholson {\em et.\ al.\ }(1995). {\em Science} 272, 509--515. and Bosh & Rivkin (1996). {\em Science} 272, 518--521). This lag seemed to remain constant throughout the ~ 180 days of the 1995 RPX however HST observations from the 1996, 1997 and 1998 oppositions show that the lag is increasing by approximately 0.6 deg/year (French {\em et.\ al.\ }(1998). {\em B.A.A.S.} 30, 1141). The baseline mean motion against which all these observations are compared, the Voyager epoch value of 587.2890 ±0.0005 deg/day, was obtained using combined Voyager 1 and 2 data (Synnott {\em et.\ al.\ }(1983). {\em Icarus} 53, 156--158). Given a possible connection between Prometheus' behavior and some features in the F ring, we present the results of a re-analysis of the Voyager data to obtain the mean motion and other orbital elements of Prometheus at the Voyager 1 and 2 epochs separately.