Penitentes are snow and ice features formed by erosion that, on Earth, are characterized by bowl-shaped depressions several tens of centimetres across, whose edges grade into spires up to several metres tall1,2,3. Penitentes have been suggested as an explanation for anomalous radar data on Europa4, but until now no penitentes have been identified conclusively on planetary bodies other than Earth. Regular ridges with spacings of 3,000 to 5,000 metres and depths of about 500 metres with morphologies that resemble penitentes have been observed by the New Horizons spacecraft5,6,7,8 in the Tartarus Dorsa region of Pluto (220°–250° E, 0°–20° N). Here we report simulations, based upon a recent model3 representing conditions on Pluto7,9, in which deepening penitentes reproduce both the tri-modal (north–south, east–west and northeast–southwest) orientation and the spacing of the ridges of this bladed terrain. At present, these penitentes deepen by approximately one centimetre per orbital cycle and grow only during periods of relatively high atmospheric pressure, suggesting a formation timescale of several tens of millions of years, consistent with crater ages. This timescale implies that the penitentes formed from initial topographic variations of no more than a few tens of metres, consistent with Pluto’s youngest terrains.
J.E.M. was supported in this work by a Discovery Grant (436252-2013) from the Natural Sciences and Engineering Research Council of Canada (NSERC) and C.L.S. was supported by a fellowship under the Integrating Atmospheric Chemistry and Physics from the Earth to Space (IACPES) Collaborative Research and Training Experience (CREATE) programme of NSERC. We thank the New Horizons team for their efforts to plan, develop and operate a mission to explore Pluto. The successful fly-by of 2015 provided publicly available data and peer-reviewed analysis of the surface and atmosphere that enabled the research presented in this paper.