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Sputnik Planitia is a nitrogen-ice-filled basin on Pluto1. Its polygonal surface patterns2 have been previously explained as a result of solid-state convection with either an imposed heat flow3 or a temperature difference within the 10-km-thick ice layer4. Neither explanation is satisfactory, because they do not exhibit surface topography with the observed pattern: flat polygons delimited by narrow troughs5. Internal heating produces the observed patterns6, but the heating source in such a setup remains enigmatic. Here we report the results of modelling the effects of sublimation at the surface. We find that sublimation-driven convection readily produces the observed polygonal structures if we assume a smaller heat flux (~0.3 mW m-2) at the base ofthe ice layer than the commonly accepted value of 2-3 mW m-2 (ref.7). Sustaining this regime with the latter value is also possible, but would require a stronger viscosity contrast (~3,000) than the nominal value (~100) considered in this study.
(ProQuest: ... denotes formulae omitted.)
Ice sublimation is a common geomorphic process at the surface of solid planets8: for instance, sublimation of carbonic ice draws a variety of spectacular depressions on the Martian south polar cap. On Earth, penitentes observed in high-altitude deserts are attributed to snow sublimation9,10. In the outer Solar System, some of Pluto's terrains rank among the most emblematic landforms created by sublimation. In summer 2015, the flyby by the New Horizons spacecraft revealed that Tombaugh Regio, sitting slightly north of Pluto's equator, is the richest province in this regard11. Owing to the specific nature of Pluto's tenuous atmosphere, N2, its most abundant constituent, is considered to be the key ingredient. The 1,000-km-wide Sputnik Planitia (SP; the western part of Tombaugh Regio) is shown by climatic models12,13 to provide the dominant source of N2 ice involved in climate cycles. Ice cycles are driven by intense condensation and sublimation on annual to astronomical timescales. Typical daily sublimation rates could reach values of 4.2 x 10-7 kg m-2 s-1 in the north of SP. Even in regions where sublimation may be less predominant such as the central-south bright cellular plains2, pronounced pits attest that net sublimation occurs at the surface in spite of the possible deposition of fresh N2 ice responsible for the high albedo. Their distribution enables...