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H. B. Hammel (SSI), K. Rages (SPRI/Ames), G. W. Lockwood (Lowell)
Observations of Neptune with the Keck 10-meter telescope (August 2000) and the Hubble Space Telescope (July 2000-June 2001) show enhanced activity in the planet's southern hemisphere. Discrete cloud features which were previously confined to narrow latitudinal bands appear to be spreading, though the major activity band remained at about 45 degrees S. Areas of more diffuse cloudiness were seen in the north, and a transient bright plume was visible near 70 degrees S in June 2001. Also, a complex of bright features extended across the equatorial region on the planet; this type of activity has only been recorded once before on Neptune, and may have been associated with the development of a Great Dark Spot in the planet's northern hemisphere at that time (Hammel et al. 1995). Furthermore, Neptune's disk-integrated brightness is now the highest it has ever been in nearly 30 years of photometric monitoring (Lockwood and Thompson 2001, in press). Together, these facts suggest that Neptune may be undergoing a transition from its recent "HST-era" state either to its earlier Voyager appearance, or to some new appearance, perhaps similar to one suggested by infrared images in the late 1970s. We will present the HST and Keck images, and if time permits, will also discuss infrared spectroscopy of Neptune taken at the IRTF with SpeX.
This work was funded in part through Grant GO-08634 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy.