Abstract
Our interpretation of the data returned by Rosetta and other cometary missions is based on the predictions of theoretical models and the results of laboratory experiments. For example, Kossacki et al. (2015) showed that 67P's surface hardness reported by Spohn et al. (2015) can be explained by sintering. The present work supports Rosetta's observations by investigating the hardening process of the near-surface layers and the change in surface morphology during insolation. In order to create as simple an analogue as possible our sample consists of pure, porous H2O ice and carbon black particles. The observations suggest that translucence of the near-surface ice is important for enabling subsurface hardening. As an end product of our experiments we also obtained carbon agglomerates with some residual strength.
Highlights
The space missions Giotto, Deep Space I, Stardust, Deep Impact, EPOXI and, most recently, Rosetta have substantially contributed to our understanding of the processes driving the activity of comets
In terms of sample height, ice loss is largely constant there is a small increase in ice loss between 0.1% and 0.5%
While the water vapour released at the surface is directly released into free space, the vapour molecules in the underlying layers travel along the vapour pressure gradient, i.e. down towards the cooler base plate, and are deposited as the temperature decreases with depth, increasing the hardness of the ice in a layer 3–6 cm below the surface
Summary
The space missions Giotto, Deep Space I, Stardust, Deep Impact, EPOXI and, most recently, Rosetta have substantially contributed to our understanding of the processes driving the activity of comets. Images of comet 67P taken by the OSIRIS imaging system (Keller et al, 2007) show a wide variety of different structures and textures. This includes dust-covered terrains, smooth terrains, ‘brittle’ materials with pits and circular structures, large-scale depressions, and exposed consolidated surfaces (El-Maarry et al, 2015; Thomas et al, 2015). Higher resolution OSIRIS data gave evidence of bright icy outcrops on the surface of 67P (Pommerol et al, 2015). These metersized bright spots are widespread on the surface within the different areas
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