Comet color changes with solar distance |
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| Authors: | William K Hartmann Dale P Cruikshank |
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| Institution: | Planetary Science Institute, 2030 East Speedway, Suite 201, Tucson, Arizona 85719, USA;Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA |
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| Abstract: | JHK colors of 14 comets are correlated with cometary distance from the Sun. The correlation could be explained by (1) changes in coma particle size as comets approach the Sun, (2) decrease in the ice/dirt ratio in coma grains as comets approach the Sun, and/or (3) phase reddening. Short-term color changes in individual comets at fixed phase angles suggest that phase reddening does not explain all color changes. Short-term changes are consistent with jets injecting fresh (high ice/dirt) nuclear material into parts of the coma. All colorimetric data are consistent with pristine coma material being relatively low-albedo dirty ice grains colored by carbonaceous dirt like that in RD-type asteroids. Ice sublimation near the Sun may leave residual pure RD dirt grains, explaining the observed color changes. |
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