Comet 17P/Holmes underwent a massive outburst in 2007 October, brightening by a factor of almost a million in under 48 hr. We used infrared images taken by the Wide-Field Infrared Survey Explorer mission to characterize the comet as it appeared at a heliocentric distance of 5.1 AU almost 3?yr after the outburst. The comet appeared to be active with a coma and dust trail along the orbital plane. We constrained the diameter, albedo, and beaming parameter of the nucleus to 4.135 ± 0.610?km, 0.03 ± 0.01, and 1.03 ± 0.21, respectively. The properties of the nucleus are consistent with those of other Jupiter family comets. The best-fit temperature of the coma was 134 ± 11?K, slightly higher than the blackbody temperature at that heliocentric distance. Using Finson-Probstein modeling, we found that the morphology of the trail was consistent with ejection during the 2007 outburst and was made up of dust grains between 250 μm and a few cm in radius. The trail mass was ~1.2-5.3 × 1010 kg.
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