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Evolution of impact melt pools on Titan

Presentation #216.05 in the session Titan III: Surface and Interior (Oral Presentation)

Published onOct 23, 2023
Evolution of impact melt pools on Titan

Titan is the only known moon with a dense atmosphere, which is composed primarily of nitrogen with a few percent of methane. Complex chemistry that occurs high in this atmosphere leads to the formation of organic hazes that fall to the surface. A main science question that remains after the Cassini mission is whether these organics mix with liquid water to form prebiotic molecules, which would be of significant astrobiological interest. Large impacts, such as those that created the Selk crater, typically heat the moon’s shallow subsurface and create liquid water melt pools. Wakita et al. (2023) performed simulations of impacts on Titan that consider a range of thermal profiles that correspond to different thicknesses of methane clathrate layers in Titan’s subsurface. Methane clathrates are stable at Titan’s surface conditions and have low thermal conductivity, making them efficient insulators that can lead to steep thermal gradients and thinning of the stagnant lid (Kalousova and Sotin, 2020). Wakita et al. (2023) showed that the clathrate layer thickness primarily influences the melt distribution while its volume is governed by the impactor size. In this follow-up study, we investigate the fate of the melt formed during the impact into a methane clathrate covered ice shell. We use an enthalpy-based numerical code that self-consistently handles the melting/freezing process as well as the flow of melt locked in the ice matrix. Our results show two different behaviors: in most of the cases, the subsurface melt pool remains close to the surface and freezes on timescales between 1 and ~20 kyr. For a few cases, we found that enough melt is produced to promote a downward-oriented transport of the partially-molten material. As it moves down, part of the melt freezes but, depending on model parameters, some melt may reach the ocean within a few kyr. Vertical impact, high surface porosity and small grain size (viscosity) are favorable for this surface-to-ocean exchange which would affect the habitability of Titan’s ocean. This study will provide key parameters that govern the evolution of a melt pool beneath a Selk-sized impact crater, which is important for the environment that will be explored by the Dragonfly mission.

References:

Kalousova and Sotin (2020), The Insulating Effect of Methane Clathrate Crust on Titan’s Thermal Evolution, GRL, 47(13), e2020GL087481, doi:10.1029/2020GL087481.

Wakita et al. (2023), Modeling the Formation of Selk Impact Crater on Titan: Implications for Dragonfly, PSJ, 4(3), 51, doi:10.3847/PSJ/acbe40.

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