title: Reorientation of Sputnik Planitia implies a subsurface ocean on Pluto.
abstract: The deep nitrogen-covered basin on Pluto, informally named Sputnik Planitia, is located very close to the longitude of Pluto's tidal axis and may be an impact feature, by analogy with other large basins in the Solar System. Reorientation of Sputnik Planitia arising from tidal and rotational torques can explain the basin's present-day location, but requires the feature to be a positive gravity anomaly, despite its negative topography. Here we argue that if Sputnik Planitia did indeed form as a result of an impact and if Pluto possesses a subsurface ocean, the required positive gravity anomaly would naturally result because of shell thinning and ocean uplift, followed by later modest nitrogen deposition. Without a subsurface ocean, a positive gravity anomaly requires an implausibly thick nitrogen layer (exceeding 40 kilometres). To prolong the lifetime of such a subsurface ocean to the present day and to maintain ocean uplift, a rigid, conductive water-ice shell is required. Because nitrogen deposition is latitude-dependent, nitrogen loading and reorientation may have exhibited complex feedbacks.
authors.affiliation: Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA.
authors.forename: F
authors.initials: F
authors.lastname: Nimmo
authors.affiliation: Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: D P
authors.initials: DP
authors.lastname: Hamilton
authors.affiliation: Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St Louis, St Louis, Missouri 63130, USA.
authors.forename: W B
authors.initials: WB
authors.lastname: McKinnon
authors.affiliation: Lunar and Planetary Institute, Houston, Texas 77058, USA.
authors.forename: P M
authors.initials: PM
authors.lastname: Schenk
authors.affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: R P
authors.initials: RP
authors.lastname: Binzel
authors.affiliation: Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Bierson
authors.affiliation: National Aeronautics and Space Administration (NASA) Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Beyer
authors.affiliation: National Aeronautics and Space Administration (NASA) Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Moore
authors.affiliation: Southwest Research Institute, Boulder, Colorado 80302, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Stern
authors.affiliation: Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA.
authors.forename: H A
authors.initials: HA
authors.lastname: Weaver
authors.affiliation: Southwest Research Institute, Boulder, Colorado 80302, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: Olkin
authors.affiliation: Southwest Research Institute, Boulder, Colorado 80302, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Young
authors.affiliation: National Aeronautics and Space Administration (NASA) Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Smith