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This article presents information on the study of distant comets in 1990. To capture comets in their unadulterated state, David Jewitt of the University of Hawaii at Manoa and others are looking far beyond Earth to regions where iceballs could exist free from the threat of solar melting and Jupiter's gravitational influence. Several of the new surveys will involve not just groundbased observations but also the careful tracking of two National Aeronautics and Space Administration spacecraft about to hurtle through the proposed Kuiper belt -- a region lying just beyond Neptune's orbit and believed to contain as many as 100 million comets. Another comet-hunting team relies on high-quality photographic plates at the Great Britain Schmidt telescope at Siding Springs Observatory, in New South Wales, Australia. Researchers compare sequential images spanning three consecutive nights, looking for slow-moving objects that display a distant comet's telltale path, or trajectory. Another method for seeking distant comets emerged in January at the American Astronomical Society meeting in Arlington, Virginia. Developed by Charles Alcock of the Lawrence Livermore National Laboratory and his colleagues, the technique relies on a well-known phenomenon called stellar occultation: When comets of large enough size pass in front of a star, they momentarily block the starlight from astronomers' view. INSET: Visitor from the Oort cloud?.

The article reports on the crumbling of Comet 73P/Schwassman-Wachmann 3. The pieces of the comet will pass within 11.7 million kilometers of Earth--the closest any comet has come to Earth in 20 years. The ongoing breakup of the comet attests that the cores of comets are fragile. The article mentions infrared images of the comet taken with the Spitzer Space Telescope.

The article reports that an analysis of images taken by the Cassini spacecraft in early June 2004, several weeks before the craft settled into orbit about Saturn, has revealed two tiny moons orbiting the ringed planet. The newly detected moons, each of which takes about a day to orbit Saturn, lie between the paths of two larger satellites, Mimas and Enceladus. The moons provide new evidence that the Kuiper belt, a reservoir of icy bodies at the solar system's outer edge, might not have quite as many small, house-size comets as planetary scientists have assumed.

Reports on images recently released showing the surprise brightening of Comet Halley, first observed in February 1991. Focus on comet's coma; Previous decrease in size and brightness of cloud; Unknown reasons for outburst.