North polar trough formation due to in-situ erosion as a source of young ice in mid-latitudinal mantles on Mars

J Alexis P Rodriguez,Ali M Bramson,Mario Zarroca,Kenneth L Tanaka,Gregory J Leonard,Victor R Baker

doi:10.1038/s41598-021-83329-3

J Alexis P Rodriguez, Ali M Bramson + Show 4 more

Open Access

https://doi.org/10.1038/s41598-021-83329-3

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Abstract

The clockwise spiral of troughs marking the Martian north polar plateau forms one of the planet’s youngest megastructures. One popular hypothesis posits that the spiral pattern resulted as troughs underwent poleward migration. Here, we show that the troughs are extensively segmented into enclosed depressions (or cells). Many cell interiors display concentric layers that connect pole- and equator-facing slopes, demonstrating in-situ trough erosion. The segmentation patterns indicate a history of gradual trough growth transversely to katabatic wind directions, whereby increases in trough intersections generated their spiral arrangement. The erosional event recorded in the truncated strata and trough segmentation may have supplied up to ~25% of the volume of the mid-latitude icy mantles. Topographically subtle undulations transition into troughs and have distributions that mimic and extend the troughs’ spiraling pattern, indicating that they probably represent buried trough sections. The retention of the spiral pattern in surface and subsurface troughs is consistent with the megastructure’s stabilization before its partial burial. A previously suggested warm paleoclimatic spike indicates that the erosion could have occurred as recently as ~50 Ka. Hence, if the removed ice was redeposited to form the mid-latitude mantles, they could provide a valuable source of near-surface, clean ice for future human exploration.

Highlights

Planum Boreum (PB), the Martian north polar plateau, consists of a water–ice cap that features a network of troughs arranged in a clockwise spiral p attern[1,2] (Fig. 1A)
Its stratigraphy includes an ancient, basal sequence of poorly preserved layers overlain by local sets of buried, frozen dunes and the much younger, well-preserved, water–ice-rich north polar layered deposits (NPLD)[1]
We used Esri’s ArcGIS software as the primary mapping and analytical tool for the spatial, topographic, and stratigraphic characterizations of troughs and undulations across the entire north polar plateau, Planum Boreum. Because this morphologic mapping required high-resolution images registered to an accurate digital elevation model (DEM), we used (~ 6 m/pixel) Mars Reconnaissance Orbiter Context Camera (CTX) and (~ 18 m/pixel) Thermal Emission Imaging System (THEMIS) VIS image mosaics georeferenced to a Mars Orbiter Laser Altimeter (MOLA) DEM (~ 115 m/pixel with a one-meter vertical accuracy)

Summary

Introduction

Planum Boreum (PB), the Martian north polar plateau, consists of a water–ice cap that features a network of troughs arranged in a clockwise spiral p attern[1,2] (Fig. 1A). There is a standing disagreement between the NPLD ages derived from geologic investigations[1,2,7] and those inferred from paleoclimatic s imulations[3,5] The latter view suggests NPLD accumulation may have started ~ 4 Ma when a decrease in Mars’ mean obliquity to ~ 25° destabilized the mid-latitude ice reservoirs, resulting in climatic conditions that facilitated water vapor transport and widespread deposition to the north pole[3,5]. In accordance with this geologic context, an estimate is that the upper few hundred meters in the NPLD, including the materials exposed within the troughs, could have formed during the last ~ 370 K a13. NPLD accumulation times of millions to hundreds of millions of years all seem plausible, and previous models of NPLD accumulation all make assumptions about processes for which much uncertainty exists

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