Penitentes as the origin of the bladed terrain of Tartarus Dorsa on Pluto

Abstract

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.

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Figure 1: The aligned ridges of Tartarus Dorsa on Pluto resemble high-latitude terrestrial penitentes.
Figure 2: Modelled growth rates of penitentes with different spacings appropriate for Tartarus Dorsa at the time of the New Horizons encounter.
Figure 3: Timing and orientation of penitentes formed, taking into account long-term variations in Pluto’s orbit.

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Acknowledgements

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.

Author information

This research was led by J.E.M., who adapted the penitente model3 to Pluto. C.L.S. led the geometric modelling efforts. A.D.T. and S.D.G. provided insights into the Plutonian atmosphere as well as output data from the PlutoWRF numerical atmospheric and surface energy balance models.

Correspondence to John E. Moores.

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The authors declare no competing financial interests.

Additional information

Reviewer Information Nature thanks D. Abbott and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Figure 1 Diagram showing the penitente geometry.

Initially a parabolic depression in a flat, horizontal surface, model penitentes were generated by rotating by the angle ω, with the positive sense indicated. The light grey region indicates the area in shadow under this orientation and projected solar zenith angle θ, shown in the negative sense.

Extended Data Figure 2 A sample run of the penitente geometry for LS = 230°, showing the distribution of received energy.

This orientation of penitentes at this time of year displays a concentration of energy near the bottom, arising from orientation and self-illumination.

Extended Data Table 1 Summary of symbols used in the penitentes dispersion relation of equation (1)

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Moores, J., Smith, C., Toigo, A. et al. Penitentes as the origin of the bladed terrain of Tartarus Dorsa on Pluto. Nature 541, 188–190 (2017). https://doi.org/10.1038/nature20779

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