Vigorous convection as the explanation for Pluto’s polygonal terrain
Abstract
Pluto’s surface is surprisingly young and geologically active. One of its youngest terrains is the nearequatorial region informally named Sputnik Planum, which is a topographic basin filled by nitrogen (N_{2}) ice mixed with minor amounts of CH_{4} and CO ices. Nearly the entire surface of the region is divided into irregular polygons about 2030 kilometres in diameter, whose centres rise tens of metres above their sides. The edges of this region exhibit bulk flow features without polygons. Both thermal contraction and convection have been proposed to explain this terrain, but polygons formed from thermal contraction (analogous to icewedges or mudcrack networks) of N_{2} are inconsistent with the observations on Pluto of nonbrittle deformation within the N_{2}ice sheet. Here we report a parameterized convection model to compute the Rayleigh number of the N_{2} ice and show that it is vigorously convecting, making RayleighBénard convection the most likely explanation for these polygons. The diameter of Sputnik Planum’s polygons and the dimensions of the ‘floating mountains’ (the hills of of water ice along the edges of the polygons) suggest that its N_{2} ice is about ten kilometres thick. The estimated convection velocity of 1.5 centimetres a year indicates a surface age of only around a million years.
 Publication:

Nature
 Pub Date:
 June 2016
 DOI:
 10.1038/nature18016
 Bibcode:
 2016Natur.534...79T