Lightcurves and revised masses of the large particles at comet 103P/Hartley 2
Abstract
Comet 103P/Hartley 2 is a hyperactive comet. Such comets have nuclei with surface areas comparable to the surface area required to sustain their water production rates, implying the surface is near 100% active. However, images of the nucleus and inner coma by the Deep Impact Flyby spacecraft show signficant localized activity, dominated by a single strong active area (A'Hearn et al. 2011, Science 332, 1396). This active area seems to be driven by carbon dioxide ice sublimation, which releases water ice into the coma (Protopapa et al. 2014, Icarus 238, 191). It has been hypothesized that this water-ice-rich material is the origin of the comet's hyperactivity, but this has not yet been definitively demonstrated.The Deep Imact spacecraft also imaged thousands of point sources surrounding the nucleus of the comet (A'Hearn et al. 2011). These sources are particles ejected by the comet, the largest of which is estimated to have a radius between 30 and 400 cm. The wide range in the radius estimate is due to the unknown photometric properties of the particles. If the particles are icy, they may contribute a significant fraction of the comet's water production rate (Kelley et al. 2013, Icarus 222, 634).To better elucidate the physical properties of the particles, we generated particle lightcurves, based on the identifications of Hermalyn et al. (2013, Icarus 222, 625) and a an independent (manual) particle search. We find no clear correlation with time or phase angle, suggesting the lightcurves are primarily driven by particle shape rather than sublimation, fragmentation, or phase effects. Three lightcurves are double-peaked, indicating rotation periods near 75 to 300 s. At least one other lightcurve suggests a rotation period of order 20 s.We also present corrections to the analysis of Kelley et al. (2013) that decrease the total large particle population mass estimates by two orders of magnitude. Despite the revision, the large particles may still account for the comet's hyperactivity if they are more like the low-albedo, ice-rich nucleus rather than high-albedo icy grains. However, an understanding of the large particle production rate is needed before definitive statements may be made.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #47
- Pub Date:
- November 2015
- Bibcode:
- 2015DPS....4750607K