Dr. Kathy Rages

December 21, 2006

“Active Atmospheres on Uranus and Neptune”

HST–GO–10534.01-A

We propose Snapshot observations of Uranus and Neptune to monitor changes in their atmospheres on time scales of weeks, months, and years. Uranus is rapidly approaching equinox in 2007, with another 4 degrees of latitude becoming visible every year. Recent HST observations during this epoch (including 6818: Hammel, Lockwood, and Rages; 8680: Hammel, Rages, Lockwood, and Marley; 8634: Rages, Hammel, Lockwood, Marley, and McKay; and 10170: Rages, Hammel, Lockwood, and Marley) have revealed strongly wavelength-dependent latitudinal structure and the presence of numerous visible-wavelength cloud features in the northern hemisphere. Long-term ground-based observations (Lockwood and Thompson 1999) show seasonal brightness changes whose origins are notwell understood. Recent near-IR images of Neptune obtained using adaptive optics on the Keck Telesccope together with images from our Cycle 9 Snapshot program (8634) show a general increase in activity at south temperate latitudes as well as the possible development of another Great Dark Spot. Further Snapshot observations of these two dynamic planets will elucidate the nature of long-term changes in their zonal atmospheric bands and clarify the processes of formation, evolution, and dissipation of discrete albedo features.