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Kerry J. Forsythe, Mark S. Marley (New Mexico State University), Heidi B. Hammel, Erich Karkoschka (Massachusetts Institute of Technology)
Recent HST observations indicate that Uranus is undergoing atmospheric changes as it moves towards equinox in 2007. These NICMOS and WF/PC HST data sets have revealed a strongly wavelength dependent latitudinal banding structure and discrete cloud features (including previously unseen cloud features in the northern hemisphere). Almost as many clouds were seen during 1998 than in the entire history of observations of the planet. It is uncertain whether these features represent seasonal variations or are merely static features that are now apparent because of changes in viewing angle. Much of the northern hemisphere is receiving direct sunlight for the first time in years. Such changes in insolation may have consequences on Uranus' physical and dynamical processes. We are continuing to monitor the planet with HST and groundbased telescopes (IRTF, Apache Point Observatory) to determine how the unusually drastic seasonal changes on Uranus affect these atmospheric processes. The brightnesses of Uranus' disk and discrete features show very strong wavelength dependence due mainly to the wavelength-dependent opacity of methane molecules. We observe the planet in narrow band filters that probe various strengths of methane absorption and hence various altitudes in the atmosphere. We will report on measurements of the height of the discrete cloud features seen in our 1998 NICMOS data and report on the continuing evolution of the atmosphere.
The author(s) of this abstract have provided an email address for comments about the abstract: keforsyt@nmsu.edu