In a paper published tonight on the Los Alamos astro-ph preprint website, astronomers described new observations of Comet Hale-Bopp at a distance of 30 astronomical units, or 2.8 billion miles, from the sun. Their conclusions:

• These observations were the most distant detection of any known comet.
• The comet’s starlike appearance and its drop in brightness since the last observations suggest that the comet has finally ceased, or is about to cease, all activity, and that they are now looking directly at the comet’s nucleus instead of the coma cloud surrounding it.
• Nonetheless, the comet is brighter than expected, which also suggests that a thin layer of new ice covers its surface and thus increases its albedo.

To quote the paper, “Observing Hale-Bopp in a completely frozen state would be extremely important because a thick coma was constantly present during the entire appariation [Ed. the fly-by of the Sun]. The coma obscured the nucleus which was not observed directly. Lack photometric data of the bared nucleus, its size — one of the most important input parameter in activity models — remains uncertain.”