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- Title
Evolution of Pluto's Impact‐Deformed Ice Shell Below Sputnik Planitia Basin.
- Authors
Kihoulou, M.; Kalousová, K.; Souček, O.
- Abstract
Sputnik Planitia basin, the dominant surface feature of the dwarf planet Pluto, is located very close to the far point of Pluto‐Charon tidal axis. This position is currently believed to be a result of whole body reorientation driven by the combination of (a) the uplift of a subsurface ocean in response to a basin‐forming impact and (b) the nitrogen layer accumulated inside the basin. Since an ice shell made of pure water ice cannot maintain the uplift on timescales of billions of years, the presence of an insulating and highly viscous layer of methane clathrates at the base of the shell has recently been proposed. In this study, we solve the thermo‐mechanical evolution of the ice shell in a 2D spherical axisymmetric geometry and evaluate the gravity anomaly associated with the evolving ice shell shape. Taking into account the effect of impact heating and stress‐dependent rheology of both ice and clathrates, we show that a thick shell (≥200 km) loses the impact heat slowly which leads to fast uplift relaxation of the order of hundreds of million years. On the contrary, a thin shell (∼100 km) cools down quickly (∼10 Myr), becoming rigid and more likely to preserve the ocean/shell interface uplift till the present. These results suggest that a thick ocean may be present beneath Pluto's ice shell. Plain Language Summary: Several icy bodies within our Solar System are believed to have harbored a subsurface ocean below an outer ice shell early in their history. During a few billions of years (Solar System age), such oceans are likely to freeze, unless supplied by additional energy sources or chemical compounds that slow down the crystallization processes. In 2015, the New Horizons mission revealed signs that the dwarf planet Pluto may have also harbored a subsurface ocean. Moreover, the unlikely position of Pluto's dominant surface feature, Sputnik Planitia basin, assumed to be formed by a giant impact, suggests that Pluto's deep ocean may still be present. One of the hypotheses explaining the basin's position assumes that the ocean/shell boundary below the basin is deformed and that its shape is stable on long timescales due to presence of a layer of highly rigid and thermally insulating clathrates. In this paper, we study the effects of more realistic rheology than assumed previously as well as those of heating due to the impact that formed the basin. We show that a rather thin ice shell (∼100 km) is more plausible than thicker shells thus implying that Pluto's ocean may be surprisingly thick (∼200 km). Key Points: We study viscous relaxation of Pluto's impact‐deformed ice shell and evolution of gravity anomaly associated with Sputnik Planitia basinStress‐dependent rheology can substantially speed up relaxation of the ice shell, while impact heating has only a minor effectThe positive gravity anomaly responsible for the basin's position can be preserved only if the ice shell is thin (∼100 km) or the ocean salty
- Subjects
NEW Horizons (Spacecraft); PLUTO (Dwarf planet); ICE; SOLAR system; GRAVITY anomalies; METHANE hydrates; SEA ice; POWER resources
- Publication
Journal of Geophysical Research. Planets, 2022, Vol 127, Issue 6, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2022JE007221