Constraining the bulk Dust to Ice Ratio and Compressive Strength for Comet Churyumov Gerasimenko Using CONSERT Radar Observations

Abstract : Using CONSERT most recent Bistatic observations in the Post-Philae landing phase we estimate the variability in the subsurface Dust to Ice ratios for comet Churyumov Gerasimenko under different dielectric hypotheses inverted from the 90 MHz radar observations and constrained by both the COSIMA and the Radio science experiments. In particular we constrain the comet dust type and ratios to the ice mass in the nucleus body. Additionally we estimat the subsurface density and porosity from CONSERT dielectric inversion and compare it to the values estimated for the upper crust from the Philae landing dynamics. Our preliminary results suggest that the comet dielectric properties are consistent with carbonated chondrites dust and water crystalline ice mixtures with very low dust concentration in the comet deep subsurface. Additionally we develop an empirical model that correlates the surface and subsurface compressive strengths to the dielectric properties. The compressive strength of both the surface and the subsurface are explored using this model using the dielectric properties inverted from the CONSERT observations. Our preliminary results suggest that the average surface compressive strength at 67P surface range from 2 kPa to 1 MPa, for a mean surface temperature of -70° C. We also analyzed the OSIRIS images of the Philae lander first impact footprints which are suggested to be ~15 cm deep into the upper regolith and hence suggesting a low surface compressive strength close to 2 kPa. The comet subsurface compressive strength of subsurface is estimated to be < 1kPa. We will discuss the implications of our results for understanding cometary formation and future sampling experiments.