Paper submitted on the atmospheric entry of comets
We’ve just submitted a new article to MNRAS discussing the atmospheric entry of cometary impactors (see the GitHub here!), which we apply to the cometary delivery of prebiotic feedstock molecules, and deposition of mass and energy in planetary atmospheres. Send me an email if you want to know more!
The atmospheric entry of cometary impactors
Richard J. Anslow, Amy Bonsor, Zoe Todd, Robin Wordsworth, Auriol Rae, Catriona McDonald, Paul Rimmer
Abstract:
The impact of comets plays an important role in the early evolution of Earth, and other terrestrial exoplanets. Here, we present a numerical model for the interaction of weak, low density cometary impactors with planetary atmospheres, which includes semi-analytical parameterisations for the ablation, deformation, and fragmentation of comets. Deformation is described by a pancake model, as is appropriate for weakly cohesive, low density bodies, while fragmentation is driven by the growth of Rayleigh-Taylor instabilities. The model retains sufficient computational simplicity to investigate cometary impacts across a large parameter space, and permits simple description of the key physical processes that control the interaction of comets with the atmosphere. We apply our model to two case studies. First, we consider the cometary delivery of prebiotic feedstock molecules. This requires the survival of comets during atmospheric entry, which is determined by three parameters: (i) the comet’s initial radius, (ii) the comet’s bulk density, and (iii) the atmospheric surface density. There is a sharp transition between the survival and catastrophic fragmentation of comets at a radius of about 150m, which increases with increasing atmospheric surface density and decreasing cometary density. Second, we consider the deposition of mass and kinetic energy in planetary atmospheres during cometary impacts, which determines the strength and duration of any atmospheric response. We demonstrate that mass loss is dominated by fragmentation, not mass ablation. Small comets deposit the entirety of their mass within a fraction of an atmospheric scale height, at an altitude determined by their initial radius. Large comets lose only a small fraction of their initial mass to ablation in the lower atmosphere.