Science and Exploration

A Billion Or More Years Of Possible Periglacial/glacial Cycling In Protonilus Mensae, Mars

By Keith Cowing
Press Release
October 29, 2022
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A Billion Or More Years Of Possible Periglacial/glacial Cycling In Protonilus Mensae, Mars
a) Example of ubiquitous surface-coverage of unit eHt by decametre-scale circular to sub-circular or quasi-polygonised structures, elevated at the margins. The margins are punctuated by boulders and show a slightly lighter tone than the terrain circumscribed by them. HiRISE image ESP_028457_2255. Examples of four morphologic categories of depressions based on similarities to impact craters. b) Type 0 – unlikely: shallow, often irregular, or elliptical in shape with no apparent rim. c) Type 1 – possible but ambiguous: similar to Type 0 but are circular in planform making them candidates for being impact related. d) Type 2 – probable: circular with uplifted rims and steeper interior wall slopes than typical of the surrounding depressions. e) Type 3 – unambiguous: bowl-shaped with sharp edges or rims and steep inward slopes. Scale bars are 20 m. North is up in all panels. 54 HiRISE ESP_028457_2255. North is up in all panels. Image credit: NASA/JPL/University of Arizona.

The long-term cyclicity and temporal succession of glacial-periglacial (or deglacial) periods or epochs are keynotes of Quaternary geology on Earth.

Relatively recent work has begun to explore the histories of the mid- to higher-latitudinal terrain of Mars, especially in the northern hemisphere, for evidence of similar cyclicity and succession in the Mid to Late Amazonian Epoch.

Here, we carry on with this work by focusing on Protonilus Mensae [PM] (43-490 N, 37-590 E). More specifically, we discuss, describe and evaluate an area within PM that straddles a geological contact between two ancient units: [HNt], a Noachian-Hesperian Epoch transition unit; and [eHT] an early Hesperian Epoch transition unit. Dark-toned terrain within the eHt unit (HiRISE image ESP_028457_2255) shows continuous coverage by structures akin to clastically-sorted circles [CSCs].

The latter are observed in permafrost regions on Earth where the freeze-thaw cycling of surface and/or near-surface water is commonplace and cryoturbation is not exceptional. The crater-size frequency distribution of the dark-toned terrain suggests a minimum age of ~100 Ma and a maximum age of ~1 Ga. The age estimates of the candidate CSCs fall within this dispersion. Geochronologically, this places the candidate CSCs amongst the oldest periglacial landforms identified on Mars so far.

Richard J. Soare, Jean-Pierre Williams, Adam J. Hepburn, Frances E. G. Butcher

Comments: 71 pages, 15 figures, published in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2210.09124 [astro-ph.EP] (or arXiv:2210.09124v1 [astro-ph.EP] for this version
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Journal reference: Mars, Icarus 385, 115115 (2022)
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Submission history
From: Frances Butcher
[v1] Mon, 17 Oct 2022 14:17:08 UTC (5,485 KB)

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