Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p43a0948w&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P43A-0948
Physics
5706 Aurorae, 5737 Magnetospheres (2756), 6275 Saturn
Scientific paper
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.
Ajello Joe
Ben-Jaffel Lotfi
Clarke John T.
Gerard Jesse
Grodent Denis
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