The Dust-to-Gas Ratio, Size Distribution, and Dust Fall-Back Fraction of Comet 67P/Churyumov-Gerasimenko: Inferences From Linking the Optical and Dynamical Properties of the Inner Comae

Abstract

In this work, we present results that simultaneously constrain the dust size distribution, dust-to-gas ratio, fraction of dust re-deposition, and total mass production rates for comet 67P/Churyumov-Gerasimenko. We use a 3D Direct Simulation Monte Carlo (DSMC) gas dynamics code to simulate the inner gas coma of the comet for the duration of the Rosetta mission. The gas model is constrained by ROSINA/COPS data. Further, we simulate for different epochs the inner dust coma using a 3D dust dynamics code including gas drag and the nucleus' gravity. Using advanced dust scattering properties these results are used to produce synthetic images that can be compared to the OSIRIS data set. These simulations allow us to constrain the properties of the dust coma and the total gas and dust production rates. We determined a total volatile mass loss of (6.1 +/- 1.5) center dot 10(9)kg during the 2015 apparition. Further, we found that power-laws withq=3.7-0.078+0.57are consistent with the data. This results in a total of5.1-4.9+6.0 center dot 109kg of dust being ejected from the nucleus surface, of which4.4-4.2+4.9 center dot 109kg escape to space and6.8-6.8+11 center dot 108kg (or an equivalent of14-14+22cm over the smooth regions) is re-deposited on the surface. This leads to a dust-to-gas ratio of0.73-0.70+1.3for the escaping material and0.84-0.81+1.6for the ejected material. We have further found that the smallest dust size must be strictly smaller than similar to 30 mu m and nominally even smaller than similar to 12 mu m.