Subglacial water on Mars Options

[ngunn]

This topic has been discussed here over a spread of time and in various threads but not recently, I think. This article might be a good way to kick off some more discussion from a present day perspective if anyone's interested:
https://www.sciencedaily.com/releases/2020/...00803120154.htm

[jccwrt]

Where we see modern evidence of glacial activity doesn't tell us much about where glaciers were located in ancient Mars. It's worth pointing out that the climate models (depending on how much stock you put into them), consistently show the highlands to be a cold trap, and that the largest cold traps are associated with the highest densities of valley networks. Even in a relatively warm and wet environment, scattered ice caps or ice sheets probably existed scattered across the highlands. We wouldn't necessarily see evidence of them, since most unambiguous glacial landforms involve either the direct presence of ice or sediments deposited by a glacier. Bear in mind that we see substantial erosion of sedimentary rocks and deposits all over the Martian surface, so unless there is unusually high-quality preservation of these landforms we're unlikely to see direct evidence of a Noachian-Hesperian ice sheet from modern topography. If those ice sheets existed, the clearest remaining evidence of them would likely be cirques and glacial valleys cut into the high-standing hardrock massifs of the highlands. Even those wouldn't be unambiguous evidence, since they'd likely be modified by fluvial and aeolian erosion in warmer/dryer epoch.

I'd also caution about extrapolating global conditions from Gale Crater. The modern rock surface is ~4 km below datum, while most valley networks are located between 1 and 3 km above datum. So the Gale Crater basin would probably be recording a much warmer environment than the valley networks. Additionally, the Gale Crater lake (estimated at 3.5 - 3.2 Ga) appears to substantially post-date the Noachian-Hesperian boundary (~3.8 Ga), and so records a slightly different slice of Martian history. So while there's ground truth for a warm, wet environment at Gale Crater, that doesn't necessarily mean that the environment the valley networks formed in was as well.

EDIT: My main research area so far has been to look at intercrater basins in the Noachian highlands, which appear to host sedimentary deposits. I have a couple of HiWish requests awaiting fulfillment targeting where the valley networks open into these basins. There is one region with a weird, speckled rock at CTX resolution that I suspect might be a tillite. This was recently picked up and I'll share it once it's in the PDS (probably next month's release).