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In this work, we present results that simultaneously constrain the dust sizedistribution, dust-to-gas ratio, fraction of dust re-deposition, and total massproduction rates for comet 67P/Churyumov-Gerasimenko. We use a 3D DirectSimulation Monte Carlo (DSMC) gas dynamics code to simulate the inner gas comaof the comet for the duration of the Rosetta mission. The gas model isconstrained by ROSINA/COPS data. Further, we simulate for different epochs theinner dust coma using a 3D dust dynamics code including gas drag and thenucleus' gravity. Using advanced dust scattering properties these results areused 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 thetotal gas and dust production rates. We determined a total volatile mass lossof $(6.1 \pm 1.5) \cdot 10^9$~kg during the 2015 apparition. Further, we foundthat power-laws with $q=3.7^{+0.57}_{-0.078}$ are consistent with the data.This results in a total of $5.1^{+6.0}_{-4.9}\cdot10^9$~kg of dust beingejected from the nucleus surface, of which $4.4^{+4.9}_{-4.2}\cdot10^9$~kgescape to space and $6.8^{+11}_{-6.8}\cdot10^8$~kg (or an equivalent of$14^{+22}_{-14}$~cm over the smooth regions) is re-deposited on the surface.This leads to a dust-to-gas ratio of $0.73^{+1.3}_{-0.70}$ for the escapingmaterial and $0.84^{+1.6}_{-0.81}$ for the ejected material. We have furtherfound that the smallest dust size must be strictly smaller than $\sim30\mu$mand nominally even smaller than $\sim12\mu$m.

frontiers in physics

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