Pluto’s Volatile and Climate Cycles on Short and Long Timescales

Abstract

The volatiles on Pluto’s surface, N2, CH4, and CO, are present in its atmosphere as well. The movement of volatiles affects Pluto’s surface and atmosphere on multiple timescales. On diurnal timescales, N2 is transported from areas of high to low insolation, and the latent heat of sublimation or condensation maintains a nearly isobaric atmosphere. On seasonal (orbital) timescales, Pluto’s atmosphere changes its 20 pressure by orders of magnitude, but most models predict that it is unlikely to collapse even at aphelion due to the equatorial N2 source in Sputnik Planitia and the high thermal inertia of the subsurface. On seasonal timescales, meters of N2 ice are transported across Pluto’s surface, but it is not yet clear from models how much of this transport is between areas which maintain N2 over an entire year (such as Sputnik Planitia) and to what extent deposition creates new volatile-covered areas (of either N2-rich or CH4-rich ice) or sublimation reveals underlying terrain. Pluto’s orbit and obliquity variations on ~3 Myr timescales (a Milankovitch cycle) induce considerable climate changes along with local accumulation or erosion of m-to-km thick layers of volatile ice. In a non-cyclical process, volatiles filled the large depression that is now Sputnik Planitia.