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Cometary dust trails were first observed by the Infrared Astronomical Satellite and consist of large refractory particles ejected from short-period comets at low velocities. Consequently, they tend to be found near the orbital paths of their parent bodies, their long and narrow appearance reminescent of airplane contrails. An examination of the entire sky as seen by IRAS has resulted in the detection of a total of eight trails associated with known short-period comets (Churyumov-Gerasimenko, Encke, Gunn, Kopff, Pons-Winnecke, Schwassmann-Wachmann 1, Tempel 1, and Tempel 2) as well as many faint trails having no known parents. Trails tended to be associated with objects having low perihelion distances that were observed near perihelion. We infer that the trail phenomenon is general to all short-period comets, and that future spacebased infrared detectors (e.g., ISO) will observe a different ensemble of trails as other comets pass through perihelion. Trail comets are found to lose the bulk of their mass in the large refractory trail particles, and are found to have a median refractory/volatile mass ratio of ≈3. This suggests that comets in general may be more like “frozen mudballs” than the canonical “dirty snowballs.” |
