Two Recently Accepted Papers in Icarus Relating to Mars Climate Change – J. Fastook

Two papers recently accepted for publication in the journal Icarus that are about work on Mars relating to investigations into early Mars climate when the atmosphere was denser and there was more water around. Both deal with the ongoing controversy about whether early Mars was “wet & warm” with rainfall to produce the observed fluvial features, or “cold & icy” with ice sheets and glaciers sequestering water that is then released as melt water to produce the fluvial features (the latter our preferred hypothesis).

Here is the “plain language” summary from the Hellas Basin paper:

Models for early Mars atmosphere and climate predict that a denser atmosphere and faint young sun together would produce cold temperatures (mean annual temperatures of ~226K) that further decrease with altitude, producing a “cold and icy highlands”.  We assess the implications of this predicted climate on snow and ice accumulation/flow on the eastern rim of the Hellas impact basin, finding that snow/ice preferentially accumulate there and glacial ice is predicted to flow down the eastern basin rim slope and out onto the basin floor, producing an integrated Hellas Glacial System. Although the basin floor is predicted to be above the melting point for only 2% of the year, we find that shear heating, thick ice and ablation can produce large volumes of liquid meltwater that can migrate vertically and laterally before freezing.  A subset of our glacial flow models and available water budget predictions corresponding to ice at Alpheus Colles Plateau at western edge of the Hellas floor suggest that the Noachian water budget may have been in the range of 1000 GEL (global equivalent layer).  Several tens of meters GEL may currently lie sequestered below a surface layer of sublimation till, and unaccounted for in current Noachian water budgets.

The second paper on the Medusae Fossae Formation was a response to the recent radar discovery of kilometer-thick ice deposits near the equator (Watters et al. 2024). We explored a high obliquity climate with UMISM (the University of Maine Ice Sheet Model), proposing a mechanism whereby they are the remnants of a larger ice sheet that as it sublimated, developed a 300-600 m thick armoring debris layer that protected it from complete removal. Water ice near the equator will be key to human occupation of Mars. “Highlights” from the article include:

·        We assess and test the recent radar-sounding findings of kms-thick ice along the equatorial region of Mars.

·      An ice sheet model, driven by results of a general circulation model, is used to characterize an ice sheet forming near the Medusae Fossae Formation.

·      Ablation of this ice deposit surface during the Amazonian provides a mechanism sufficient to form the thick capping layer.