HR: 1340h
AN: P43A-0948    [Abstracts]
TI: HST/ACS UV Imaging of Saturn's Southern Aurora in a Quiet State
AU: * Wannawichian, S
EM: suwichaw@bu.edu
AF: Center for Space Physics Boston University, 725 Commonwealth Ave, Boston, MA 02215 United States
AU: Clarke, J T
EM: jclarke@bu.edu
AF: Center for Space Physics Boston University, 725 Commonwealth Ave, Boston, MA 02215 United States
AU: Gerard, J
EM: JC.Gerard@ulg.ac.be
AF: University of Liege, Allee du 4 Aout - Sart Tilman, Liege, B4000 Belgium
AU: Grodent, D
EM: D.Grodent@ulg.ac.be
AF: University of Liege, Allee du 4 Aout - Sart Tilman, Liege, B4000 Belgium
AU: Pryor, W R
EM: wayne_pryor@centralaz.edu
AF: Central Arizona College, 8470 N. Overfield Road, Coolidge, AZ 85228 United States
AU: Ajello, J
EM: jajello@jpluvs.jpl.nasa.gov
AF: Jet Propulsion Lab., 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Benjaffel, L
EM: bjaffel@iap.fr
AF: Institut d"Astrophysiques du CNRS, 98 bis Boulevard Arago, Paris, 75014 France
AB: Prior observations of Saturn's aurora have suggested that the aurora are highly variable, with much of the activity controlled by conditions in the solar wind. Observations of Saturn's UV aurora on 17 February 2005 were performed with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) to further test this. The UV Solar Blind Camera (SBC) imaged the UV emissions from 115.0 to 170.0 nm for a period of 5 HST orbits, or 8 hours, corresponding to 74% of a Saturn rotation. In that observation period, HST imaged the southern auroral region in sunlight, but not the northern auroral region because of the tilt of Saturn rotation axis. Saturn's aurora appeared in its most quiet state, comparable or fainter than those observed by HST's Space Telescope Imaging Spectrograph (STIS) in January 2004. Discrete emissions were detected, with some evidence of latitudinal variations of localized emissions and motions. At the same time, Cassini's Ultraviolet Imaging Spectrograph (UVIS) studied the intensity and spectral distribution of Saturn's northern night side emission region. With the benefit of simultaneous observations, we found that the characteristics of Saturn's emission region in the day side southern aurora appeared correlated with Saturn kilometric radio (SKR) emissions, charged particles and magnetic field measurements in the night side Saturn magnetosphere. The faint UV aurora are consistent with the previously reported correlation between radio and UV emissions, and the low disturbance in Saturn's magnetosphere observed by Cassini. In this quiet state, the auroral oval brightness is a few kilorayleighs (KR). The summed images show evidence of an offset auroral oval toward midnight responding to solar wind pressure and more diffuse features in the dusk side. The specific properties of Saturn's aurora in its minimum state will be presented, and compared with more active periods.
DE: 5706 Aurorae
DE: 5737 Magnetospheres (2756)
DE: 6275 Saturn
SC: Planetary Sciences [P]
MN: Fall Meeting 2005