Images were significantly smeared and degraded spatial resolution with the FOS and the Goddard High Resolution Spectrograph (GHRS) resulted from the need to use wider apertures to observe selected features. Still, planned and serendipitous observational opportunities demonstrated the utility of HST.
On September 18, 1990, observations with the Faint Object Camera (FOC) of Pluto and Charon were obtained ( Albrecht, 1991) which showed that the images were far superior to groundbased data. The planet and its moon were distinctly separated, providing a basis for improving values of mass ratio and orbital parameters.
Amateur astronomers reported a white spot on Saturn on September 25, 1990.
Although the zenith angle was about 65
at sunset, subsequent
groundbased observations revealed that an equatorial disturbance was underway.
Two similar disturbances were observed in 1876 and 1933; thus, this event was
significant enough for planetary scientists to petition the director, Riccardo
Giacconi, for discretionary time to observe the event. The earlier August data
were combined with multicolor planetary camera mode (PC) images, spanning more than two full rotations of the planet, on November 17 and 18, 1990, and
post-disturbance 6-color observations on June 5 and 6, 1991. Color ratios,
variations in zonal wind speeds and characterizations of traveling waves were
interpreted as atmospheric responses to a single convective bubble which had
emerged at 4
N latitude ( Barnet et al., 1992;
Beebe et al., 1992; Westphal et al., 1992).
The arrival of the Ulysses spacecraft at Jupiter in February 1992 led to a coordinated set of observations. The first UV images of the jovian aurora were obtained. These observations, combined with those of the Saturn storm, established that the WFPC-1, even with spherical aberration, had considerable utility for planetary observations. The ultraviolet sensitivity of the HST instruments provided new capabilities for studying upper atmospheres and surface reflectivities, and the improved spatial resolution relative to groundbased imaging, and increased frequency resolution relative to the International Ultraviolet Explorer (IUE), promised significantly enhanced capabilities.
Successful completion of the first refurbishment mission in December 1993 led to the installation of the Corrective Optics Space Telescope Axial Replacement (COSTAR), Wide Field/Planetary Camera 2 (WFPC-2), new gyroscopes and improved solar cells. Although this refurbishment restored most of the planned capabilities, it is but the first of a series of expected service missions. Preparation for installation of instruments with infrared capabilities in 1997 is underway and plans for a replacement of WFPC-2 have begun. By 1999, when a orbit re-boost of the telescope will be needed, WFPC-2 will have been in orbit for 5 years. This is more than its expected lifetime, thus an Advanced Camera is being planned. The WFPC-2 and FOS have narrow fields of view. The Advanced Camera would have a field of view of 3-4 arcminutes and a pixelation (spatial sampling) twice that of the PC mode of WFPC-2. It would be sensitive in the optical to near-infrared range ( Brown, 1993).
The campaign for observing the impacts of the Comet Shoemaker-Levy 9 fragments on July 16-22 and the possibility of coordinated atmospheric observations with the Galileo spacecraft in 1995-7 promise that HST will make a significant contribution to our understanding of the jovian system. In the meantime, planetary astronomers have acquired data sets that will increase our general understanding of the solar system.