title: Convection in a volatile nitrogen-ice-rich layer drives Pluto's geological vigour.
abstract: The vast, deep, volatile-ice-filled basin informally named Sputnik Planum is central to Pluto's vigorous geological activity. Composed of molecular nitrogen, methane, and carbon monoxide ices, but dominated by nitrogen ice, this layer is organized into cells or polygons, typically about 10 to 40 kilometres across, that resemble the surface manifestation of solid-state convection. Here we report, on the basis of available rheological measurements, that solid layers of nitrogen ice with a thickness in excess of about one kilometre should undergo convection for estimated present-day heat-flow conditions on Pluto. More importantly, we show numerically that convective overturn in a several-kilometre-thick layer of solid nitrogen can explain the great lateral width of the cells. The temperature dependence of nitrogen-ice viscosity implies that the ice layer convects in the so-called sluggish lid regime, a unique convective mode not previously definitively observed in the Solar System. Average surface horizontal velocities of a few centimetres a year imply surface transport or renewal times of about 500,000 years, well under the ten-million-year upper-limit crater retention age for Sputnik Planum. Similar convective surface renewal may also occur on other dwarf planets in the Kuiper belt, which may help to explain the high albedos shown by some of these bodies.
authors.affiliation: Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St Louis, Saint Louis, Missouri 63130, USA.
authors.forename: William B
authors.initials: WB
authors.lastname: McKinnon
authors.affiliation: Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA.
authors.forename: Francis
authors.initials: F
authors.lastname: Nimmo
authors.affiliation: Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St Louis, Saint Louis, Missouri 63130, USA.
authors.forename: Teresa
authors.initials: T
authors.lastname: Wong
authors.affiliation: Lunar and Planetary Institute, Houston, Texas 77058, USA.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Schenk
authors.affiliation: National Aeronautics and Space Administration (NASA) Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: Oliver L
authors.initials: OL
authors.lastname: White
authors.affiliation: Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Roberts
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: J R
authors.initials: JR
authors.lastname: Spencer
authors.affiliation: Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22904, USA.
authors.forename: A D
authors.initials: AD
authors.lastname: Howard
authors.affiliation: National Aeronautics and Space Administration (NASA) Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: O M
authors.initials: OM
authors.lastname: Umurhan
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