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H. B. Hammel (Space Science Institute), G. W. Lockwood (Lowell), K. A. Rages (SPRI/Ames), M. Marley (Ames)
A campaign to understand seasonal changes on Uranus returned a variety of results in 2000. On 5-8 June 2000, disk-resolved images and spectroscopy of Uranus at 0.8-2.5 microns were obtained at the NASA IRTF. The spectra reveal hemispheric asymmetry, and will allow discrimination of vertical aerosol models at different latitudes on the planet.
On 16-18 June, 7 August, and 9 October 2000, the Hubble Space Telescope produced visible and near-infrared images. At least six discrete features were detected, and wind speeds were measured for features as far north as +42 deg. Initial results suggest that winds are not symmetric with respect to the planet's equator.
On 9-11 August 2000, images were also obtained in the near infrared (roughly J, H, and K') with the Keck 10-m Adaptive Optics system. The Keck images show at least four discrete features roughly at latitudes. Two southern features were seen on two nights, and have wind speeds commensurate with earlier determinations for those latitudes. Two northern features were each detected on only one night, but comparison with HST data may allow accurate wind speeds to be extracted.
In both June and August 2000, the highest-contrast features were seen near +42 deg on the far northern limb (the October data are limited in longitude). Features seen in 1998, which now should be well away from the limb, are presently not detectable. One explanation is that the northernmost features are relatively short-lived, appearing briefly on the newly sunlit limb and then fading within a few years. On the other hand, features at southern midlatitudes have been consistently detected since 1994, perhaps suggesting that different mechanisms for discrete cloud formation are active on Uranus.
Support for the Keck observations was provided by NASA grant NAG5-7853; Uranus HST work is supported through NASA/STScI grants GO-08680.05-A and GO-08634.06-A.