Reorientation of Sputnik Planitia implies a Subsurface Ocean on Pluto

TL;DR

This paper proposes that Pluto's Sputnik Planitia reorientation can be explained by the presence of a subsurface ocean, which causes a positive gravity anomaly through shell thinning and uplift, supported by geological and physical modeling.

Contribution

It introduces a novel explanation linking Sputnik Planitia's location and gravity anomaly to a subsurface ocean on Pluto, supported by impact and reorientation models.

Findings

A subsurface ocean explains the gravity anomaly and reorientation.

Without an ocean, a thick nitrogen layer is implausible.

Shell thinning and ocean uplift are key to the observed features.

Abstract

The deep nitrogen-covered Sputnik Planitia (SP; informal name) basin on Pluto is located very close to the longitude of Pluto's tidal axis[1] and may be an impact feature [2], by analogy with other large basins in the solar system[3,4]. Reorientation[5-7] due to tidal and rotational torques can explain SP's location, but requires it to be a positive gravity anomaly[7], despite its negative topography. Here we argue that if SP 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 N2 deposition. Without a subsurface ocean a positive gravity anomaly requires an implausibly thick N2 layer (greater than 40 km). A rigid, conductive ice shell is required to prolong such an ocean's lifetime to the present day[8] and maintain ocean uplift. Because N2 deposition is latitude-dependent[9], nitrogen loading and reorientation may have exhibited complex feedbacks[7].