Planetary science: Pluto's telltale heart.

Studies of a large frost-filled basin on Pluto show that this feature altered the dwarf planet's spin axis, driving tectonic activity on its surface, and hint at the presence of a subsurface ocean. See Letters p.86 , p.90 , p.94 & p.97 Tanguy Bertrand and Francois Forget have developed a model for volatile transport on Pluto and use it to simulate the evolution of N2, CH4 and CO on the dwarf plant over tens of thousands of Earth years. The model predicts N2 ice accumulation in the deepest low-latitude basin and the threefold increase in atmospheric pressure that has been observed to occur since 1988. This points to atmospheric–topographic processes as the origin of the prominent equatorial N2 glacier known as Sputnik Planitia (formerly Sputnik Planum). This is one of four papers on the geology of Sputnik Planitia in this issue of Nature. In News & Views, Amy Barr puts these latest contributions into context. James Keane et al. report that the location of Sputnik Planitia, the approximately 1,000-kilometre-diameter topographic basin that dominates the surface of Pluto, is a natural consequence of the infill of volatile ices within the basin and the resulting reorientation (true polar wander) of the dwarf planet. As Sputnik Planitia slowly loaded with volatiles, the pull of tidal torques from Charon would have resulted in the eventual alignment of the basin with the Pluto–Charon tidal axis. Sputnik Planitia probably formed northwest of its present location, and was loaded with volatiles over million-year timescales as a result of volatile transport cycles. This is one of four papers on the geology of Sputnik Planitia in this issue of Nature. In News & Views, Amy Barr puts these latest contributions into context. The present location of Sputnik Planitia—the prominent deep icy basin on Pluto—is close to one of the longitudes of the dwarf planet's tidal axis. By analogy with other large basins in the Solar System, it is thought to be an impact feature. Although reorientation arising from tidal and rotational torques can explain the present-day location of the basin, it requires the feature to be a positive gravity anomaly, despite its negative topography. Francis Nimmo et al. argue that if Sputnik Planitia formed via impact and if Pluto possesses a subsurface ocean, a positive gravity anomaly would naturally result because of shell thinning and ocean uplift, followed by later modest nitrogen deposition. This is one of four papers on the geology of Sputnik Planitia in this issue of Nature. In News & Views, Amy Barr puts these latest contributions into context. Douglas Hamilton et al. present modelling data that imply that Pluto's Sputnik Planitia basin may be an ice cap, rather than the product of an impact. Their data suggest that the feature formed shortly after Pluto's largest satellite Charon did, and has since been stable, with its latitude corresponding to a minimum in annual solar illumination over its orbital precession period of about a million years, and its longitude determined by tidal forces from Charon. This is one of four papers on the geology of Sputnik Planitia in this issue of Nature. In News & Views, Amy Barr puts these latest contributions into context.