Pluto'S Antipodal Terrains Imply A Thick Subsurface Ocean And Hydrated Core

Recent analysis of New Horizons data revealed an similar to 1,000-km-diameter region of large-scale lineations antipodal to Sputnik Planitia, the 1,200 x 2,000 km elliptical impact basin on Pluto's anti-Charon hemisphere. At the available resolution, these lineations are similar to antipodal terrains associated with large impact basins elsewhere in the Solar System. Here, we simulate the Sputnik Planitia-forming impact and track stress waves through a Pluto-like target body to the antipode. We find that the Sputnik Planitia-forming impact is capable of producing significant antipodal terrains and the observed lineations may be extensional graben. The extent and mode of deformation at the antipode, however, is sensitive to ocean thickness and core composition. Simulations that best reproduce the observed terrains imply that Pluto may have hosted a >150-km-thick ocean and a hydrated core at the time of impact.Plain Language Summary Pluto's interior structure remains largely a mystery, including the composition of the core and the existence and extent of a subsurface ocean. Though seismological study is not yet possible on Pluto, the reaction of a planet's interior structure to stress waves produced by large impacts can be used to indirectly probe the planet's interior-seismology by impact. We use impact modeling to simulate the formation of Sputnik Planitia, Pluto's massive impact basin, to determine how the dwarf planet's interior controls transmission of stress waves to the opposite hemisphere. Our results suggest that a large subsurface ocean beneath the ice shell, as well as a core that has experienced substantial alteration from interactions with an ocean above, are critical to match the size of the lineated terrain observed antipodal to Sputnik Planitia.Key Points.We model the formation of Pluto's Sputnik Planitia basin from an impact origin to assess the dwarf planet's interior structureOur simulations illustrate the Sputnik Planitia-forming impact is capable of producing significant antipodal terrains on PlutoThe extent and mode of deformation at the antipode is most consistent with a thick (>150-km) ocean and a hydrated core