Properties of the dust in the coma of 67P/Churyumov-Gerasimenko observed with VIRTIS- M

An investigation is presented of the dust scattering in the coma of 67P/Churyumov- Gerasimenko for the dates of 2015 February 28, March 15 and April 27. A comparison of the morphology of dust continuum maps at 1.1 μm and gas emission shows that for the above dates the spatial distribution of the dust is strongly correlated with H₂O but not with CO₂ emission. For April 27, the radial profile on the illuminated side of the nucleus in the inner coma agrees well with the direct simulation Monte Carlo (DSMC) calculations as the dust is accelerating and flows outwards but follows a 1/ρ distribution at distances larger than 4 km from the nucleus. The azimuthal distribution of the dust is narrower than the broader emission of the gas. Afρ values are 1.13 m for 2015 February 28, 2.02 m for April 27, while local values for March 15 are 2.3-5.3 m, depending on the nucleus illumination. In the inner coma, the spectral reflectivity from 0.35 to 3.5 μm displays a red slope with a change at around 1 μm. From 0.35 to 0.8 μm, the values range from 9 to 12 ± 1 per cent per 100 nm both on the sunlit side and on the dark side. From 1 to 2.5 μm, the values are 1.7 ± 0.2 per cent per 100 nm on the sunlit side and 3 ± 1 per cent per 100 nm on the dark side. For the August 26 jet, no significant increase of the colour gradient with distance from the nucleus could be observed, nor any significant difference detected between the jet and the background coma.