Investigating the Geophysical Control of 67P/Churyumov-Gerasimenko’s Outburst Plumes

Scientific Goals
Cometary outbursts (transient, rapid material ejections from the comet’s nucleus) have been observed from the ground for decades, many of which appear to result from the ejection of highly collimated plumes of materials from the comet’s nucleus. Recently, the Rosetta mission to comet 67P/Churyumov-Gerasimenko has provided the first high-resolution observations of such outburst plumes as they leave the nucleus. Long thought to be controlled by internal processes, Rosetta revealed that some outburst plumes result from mass-wasting events at the surface of the nucleus. Further analysis revealed that the morphology of some of these outburst plumes are consistent with avalanches of material moving downslope into active regions on the nucleus. However, the effects of topography, geomorphology, and material properties on the appearance of mass-wasting-driven outburst plumes has not been studied. For example, differences in the morphology of the avalanching region and material, active area shape and composition, slope structures, and solar phase angle may result in different appearances and behaviors of outbursting regions. We propose to systematically investigate how differences in these surface structures and materials affect the behavior and morphology of outburst plumes, and constrain which outbursts on 67P could be driven by mass-wasting.

Methodology
We will use numerical models to explore how geophysical processes and geomorphological structures on the surface of Comet 67P affect the appearance and behavior of comet outbursts. These models use sublimative thermodynamics and rarefied gas dynamics to simulate the interactions between dust grains and between dust grains and sublimating gases outgassing near the surface of the nucleus. We will use these numerical models, already developed to simulate plumes on on active comets and other small bodies, to conduct a sensitivity study that investigates how different shapes and compositions of the avalanche source material and active area affect observed outburst plume morphology. We will also simulate different surface structures observed in the shape of 67P to understand how such structures affect the appearance and behavior of the observed outburst plumes. The outputs of these models will be compared to Rosetta observations, to connect the observed outbursts with geophysical processes at the surface of the nucleus.