Constraints on the ejecting-crust activity model on comet 67P/Churyumov-Gerasimenko

Abstract

Reproducing the observed activity of comets with thermophysical models remains a primary challenge of cometary science. We use a pebble-based thermophysical model of gas-pressure build-up in the subsurface to reproduce the global emission rates of dust, water, CO${}_2$, and CO observed by Rosetta at comet 67P/Churyumov-Gerasimenko (hereafter 67P). For sufficiently low diffusivities, the low tensile strength is overcome, leading to the ejection of $\sim$ millimetre- to decimetre-sized dust-particles as well as roughly the correct outgassing rates. All the ejections, and thus the bulk of the outgassing, come from the southern hemisphere during the time that it is strongly illuminated at perihelion. This leads to a 'blow-off' of the dust-crust that otherwise forms: volatiles are much closer to the surface in the south (within the top centimetre) than in the north (10-or-more cm deep), naturally explaining the strong southern water-outgassing expected from 67P's non-gravitational accelerations and torques. We find that low gas-diffusivity, as well as large heat-capacity and steeply decreasing tensile strength with depth or ice-content, are in best agreement with the outgassing data. However, even in these cases, we struggle not to exceed the observed emission rates of dust, CO${}_2$, and CO. In the south, it is difficult for models to achieve a balance between triggering activity and generating too much of it (with CO${}_2$ the critical driving-species here); while in the north, it remains challenging to generate activity at all. Strong constraints are placed on the nature of the activity mechanism by the location of dust-ejection and erosion.

13 pages, 13 figures, accepted for publication in MNRAS

References in corpus (12)

• Evidence for the formation of comet 67P/Churyumov-Gerasimenko through gravitational collapse of a bound clump of pebbles
• Seasonal Mass Transfer on the Nucleus of Comet 67P/Chuyumov-Gerasimenko
• The thermal, mechanical, structural, and dielectric properties of cometary nuclei after Rosetta
• Thermophysical evolution of planetesimals in the Primordial Disk
• Tensile Strength of Porous Dust Aggregates
• Airfall on Comet 67P/Churyumov-Gerasimenko
• Modelling the water and carbon dioxide production rates of Comet 67P/Churyumov-Gerasimenko
• Activity distribution of comet 67P/Churyumov-Gerasimenko from combined measurements of non-gravitational forces and torques
• A quantitative description of comet 67P's dust and gas production remains enigmatic
• Varying water activity and momentum transfer on comet 67P/Churyumov-Gerasimenko from its non-gravitational forces and torques
• Diurnal ejection of boulder clusters on comet 67P lasting beyond 3 AU
• Ejection and Dynamics of Aggregates in the Coma of Comet 67P/Churyumov-Gerasimenko