Dust in Comet 103P/Hartley 2 coma during EPOXI mission
Résumé
The Deep Impact spacecraft flew by Comet 103P/Hartley 2 on 4 November 2010 (EPOXI mission). In situ observations are complemented by a systematic ground- and space-based observation campaign. In the present work, imaging polarimetry is used to emphasize different dust regions in the coma and follow their evolution over a period including the EPOXI fly-by. On the intensity images, the coma is asymmetric with an important tailward feature. Jets in the sunward direction are observed to present an extension that depends on the nucleus phase. The azimuthal integrated intensity presents a nominal radial decrease (−1 in log-log scale) for optocentric distances larger than a few hundred kilometers. Through cometary continuum narrow band filters, the aperture polarization decreases with the optocentric distance. On the polarization maps, the short sunward jets are more polarized than other parts of the coma. Intensity variations may be induced by large slow particles in the inner coma and possibly by their fragmentation into smaller particles, under ice sublimation processes. The decrease of linear polarization with increasing optocentric distance is correlated with intensity variations and may be induced by the same physical process. The optical behavior of 103P/Hartley 2 is finally compared to those of other Jupiter-family comets such as Comet 9P/Tempel 1 impacted by the Deep Impact projectile in 2005 and Comet 67P/Churyumov-Gerasimenko, target of the Rosetta mission (2014-2015), since the polarimetric properties of both comets have been monitored remotely in the recent past.