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

TL;DR

This paper proposes that penitentes, ice-sculpted features observed on Earth, are the origin of the bladed terrain in Tartarus Dorsa on Pluto, supported by simulations matching observed morphology and formation timescales.

Contribution

It is the first to identify penitentes as the likely cause of Pluto's bladed terrain, adapting terrestrial models to Pluto's conditions and explaining observed feature orientations and spacing.

Findings

Simulations reproduce the observed penitente-like features on Pluto.

Penitentes deepen by about 1 cm per orbital cycle, forming over tens of millions of years.

Formation is linked to periods of high atmospheric pressure on Pluto.

Abstract

Penitentes are ablative features observed in snow and ice that, on Earth, are characterized by regular cm to tens of cm spaced bowl-shaped depressions whose edges grade into tall spires up to several meters tall (Nichols et al. 1939, Lliboutry et al. 1954, Claudin et al. 2015). While penitentes have been suggested as an explanation for anomalous radar data on Europa (Hobley et al. 2013), hitherto no penitentes have been identified conclusively on other planetary bodies. Regular ridges with spacing of 3000 m to 5000 m and a depth of $\sim500$ m with morphologies that resemble penitentes (Fig. 1) have been observed by the New Horizons spacecraft (Moore et al. 2016, Stern et al. 2015, Gladstone et al. 2016, Moore et al. 2017) in the Tartarus Dorsa (TD) region of Pluto (approximately 220-250$^\circ$ E, 0-20$^\circ$ N). Here we report simulations, based upon a recent model (Claudinet al. 2015) adapted to conditions on Pluto (Gladstone et al. 2016, Toigo et al. 2015), that reproduce both the tri-modal orientation and the spacing of these features by deepening penitentes. These penitentes deepen by of order 1 cm per orbital cycle in the present era and grow only during periods of relatively high atmospheric pressure, suggesting a formation timescale of several tens of millions of years, consistent with cratering ages and the current atmospheric loss rate of methane. This time scale, in turn, implies that the penitentes formed from initial topographic variations of no more than a few 10s of meters, consistent with Pluto's youngest terrains.