Cometary activity and surface evolution

Abstract

Cometary surfaces evolve on a different time scale than most Solar System objects. Because changes are principally driven by the sublimation of volatiles in the subsurface, most changes take place when the comet orbit brings the nucleus within the inner Solar System, for a time period that typically lasts a few 104 years before the nucleus becomes extinct or disintegrates. Recent work based on the analysis of several comets visited by space missions, especially Rosetta, has shown that the large scale topography of cometary nuclei is mostly controlled by events which took place in the Outer Solar System. Tall cliffs and deep pits are more likely to be the outcome of impacts in the primitive Kuiper Belt or large scale outbursts when the comet was in its Centaur phase, rather than being due to the current sublimation. Indeed, water driven activity (<3AU) tends to not carve large features in the surface, but instead breaks apart the topography in smaller features, until the surface is dominated by a sooth layer of pebbles and dust (e.g. comet 103P/Hartley 2). Therefore, the large scale roughness of cometary nuclei provides a measure of how evolved the surface is, and can be used as a crude datation tool to assess how long the comet has been in the inner Solar System.