Dynamics of Crystalline Silicates in the Coma of Comet 9P/Tempel and the Deep Impact Ejecta

Details Dynamics of Crystalline Silicates in the Coma of Comet 9P/Tempel and the Deep Impact Ejecta Dynamics of Crystalline Silicates in the Coma of Comet 9P/Tempel and the Deep Impact Ejecta

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.2824k&link_type=abstract

American Astronomical Society, DPS meeting #42, #28.24; Bulletin of the American Astronomical Society, Vol. 42, p.964

Astronomy and Astrophysics

Astronomy

Scientific paper

Mid-infrared spectra have revealed the presence of crystalline silicates in the dust of comet 9P/Tempel, both before and after the Deep Impact cratering experiment (Wooden et al. 2010, 42nd DPS Meeting). The spectra of the Deep Impact ejecta reveal strong silicate emission features, including resonances from Mg-rich crystalline silicates (forsterite and enstatite), reminiscent of spectra of comet C/1995 O1 (Hale-Bopp). In constrast, spectra of the ambient coma appears to be that of a typical ecliptic comet: a weak 10 micron silicate plateau with subtle features attributable to forsterite. Wooden et al. (2010) examine the time evolution of archival Spitzer Space Telescope spectra of the Deep Impact ejecta and find that crystalline silicates are present in the ejecta as late as 40 hours post-impact. They also find that the spectra at these late epochs have the same spectral shapes as the ambient coma. Thus, the slower moving ejecta and the ambient coma are both composed of large porous aggregates containing crystalline silicates. We examine the dynamics of dust ejected by Deep Impact and find that this slower moving ejecta is at least 10 microns in size. This result implies that the ambient coma of 9P/Tempel is dominated by grains with sizes of order 10 microns. If we generalize our results, we conclude that many ecliptic comets may be dominated by large porous grains with high crystalline fractions, approximately 40% by mass, despite their weak silicate emission features.
This research is supported by NASA's Planetary Atmospheres Program.

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