Curious Mars

Geologic Constraints on Early Mars Climate


Early Mars

Early Mars climate research has well-defined goals (Mars Exploration Program Analysis Group 2018). Achieving these goals requires geologists and climate modelers to coordinate.

Coordination is easier if results are expressed in terms of well-defined parameters. Key parameters include the following quantitative geologic constraints. (1) Cumulative post-3.4 Ga precipitation-sourced water runoff in some places exceeded 1 km column. (2) There is no single Early Mars climate problem: the traces of ≥2 river-forming periods are seen. Relative to rivers that formed earlier in Mars history, rivers that formed later in Mars history are found preferentially at lower elevations, and show a stronger dependence on latitude. (3) The duration of the longest individual river-forming climate was >(102-103) yr, based on paleolake hydrology. (4) Peak runoff production was >0.1 mm/hr. However, (5) peak runoff production was intermittent, sustained (in a given catchment) for only <10% of the duration of river-forming climates. (6) The cumulative number of wet years during the valley-network-forming period was >105 yr. (7) Post-Noachian light-toned, layered sedimentary rocks took >107 yr to accumulate. However, (8) an "average" place on Mars saw water for <107 yr after the Noachian, suggesting that the river-forming climates were interspersed with long globally-dry intervals. (9) Geologic proxies for Early Mars atmospheric pressure indicate pressure was not less than 0.012 bar but not much more than 1 bar.

A truth table of these geologic constraints versus currently published climate models shows that the late persistence of river-forming climates, combined with the long duration of individual lake forming climates, is a challenge for most models.

Edwin S. Kite
(Submitted on 31 Dec 2018)

Comments: Accepted by Space Science Reviews
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1812.11722 [astro-ph.EP] (or arXiv:1812.11722v1 [astro-ph.EP] for this version)
Submission history
From: Edwin Kite
[v1] Mon, 31 Dec 2018 08:32:21 UTC (3,442 KB)

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