Physical properties of dust in comets: a post-Rosetta understanding
Abstract
The combination of investigations on dust particles within comet 67P/Churyumov-Gerasimenko (67P/C-G) from the Rosetta mission, from remote observations of their light scattering properties, and from theoretical and experimental studies, is providing an unprecedented insight into the structure, formation and early evolution of comets. Through its 26 months-length duration, Rosetta has provided a ground-truth for the high porosity of the nucleus, with studies of CONSERT experiment suggesting that the porosity increases inside the nucleus and that a major component of the nucleus consists of refractory carbonaceous compounds [1-4]. It has also established the aggregated structure of dust particles within a wide range of sizes in the inner coma, with, e.g., MIDAS experiment giving evidence for the hierarchical fractal structure of dust particles, down to tens of nm-sized grains [5-6].
Such discoveries confirm previous interpretations of remote observations of solar light scattered by dust in cometary comae, which have suggested for a few comets, including 67P/C-G, the presence of fractal, likely porous aggregates, and of more compact particles within the coma [7,8]. Some drastic changes in remote polarimetric observations of comets during fragmentation or disruption events could have been clues to differences in structure between the surface and the interior of their nuclei. Finally, the significance of such results for the possible survival and delivery of the surface of telluric planets of organics after heavy bombardment event(s) in the early Solar System will be discussed.
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