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As the discussion progresses from the likelihood that there is water on Mars through yes, near the poles, now to to Is there really a frozen lake near the equator on Mars? and There's a lot of subsurface water ice at many mid-latitude sites..., I'm wondering how a water resources map will be generated in the next few decades to identify the best candidate locations for water-intensive efforts such as making methalox and growing food.

Would the workhorse likely be a few satellites with neutron detectors, or multi-spectral radar, or sensitive hyperspectral vis-IR imagery, or is there not much room for improvement on space-based observation and the search would have to be done by surface or lower atmospheric craft (e.g. rovers and aircraft)?

Some of the earlier data is mentioned in answers to the question What's the scientific evidence of water for return trip methalox on Mars?

update: There are some problems with some observations: Help understanding the false MRO observations of hydrated minerals on Mars

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In addition to vis-IR and radar, I think we may see a set of satellites similar to GRACE, which compared gravity maps over time to visualize changing aquifers on Earth. Watching the equatorial zones during the summer months would give us a good idea of where water was in which seasons, where it moved, and where it stays regularly consistent.

But ultimately, we're going to need to probably do some correlation on this stuff, and that will mean rovers. We can match the expected water levels to what we'd see on Earth and our models of Mars, but at some point we're going to have to send something with a big drill or shovel to actually verify that yes there is water ice in the volumes we expect, and yes it is clean enough to be usable for our purposes.

EDIT: I want to clarify in response to some of the (absolutely correct) comments. It would be difficult to detect using purely gravitational analysis, and the CO2 cycle on Mars is likely to produce a significant amount of noise. However, with careful analysis we could still glean some data from gravitational mapping. For example, CO2 sublimates at -78.5 C, while H2O sublimates at 0 C. Mapping surface temperature alongside the gravitational changes would likely allow us to separate CO2 and H20 sublimation.

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  • $\begingroup$ Interesting! What forces might cause water to move on Mars? I'd thought that water is expected to be in solid form;wouldn't this movement imply liquid water and that it is replenished by rainfall? After millions of years of no rain, wouldn't some static equilibrium be reached? $\endgroup$
    – uhoh
    Commented Jun 19, 2018 at 1:29
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    $\begingroup$ If we're looking to detect ice in the top meter or so of the crust, we could maybe just drop small but dense impactors (lumps of Phobos rock, for instance) and look at the spectrum of the flare when they hit. $\endgroup$
    – Steve Linton
    Commented Jun 19, 2018 at 9:09
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    $\begingroup$ The problem is - Mars has CO2 cycle and it is more intensive (freezing-sublimation) than water cycle. Because of this I doubt that gravity observation will be useful for monitoring of water on Mars. $\endgroup$
    – Heopps
    Commented Jun 19, 2018 at 11:05
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    $\begingroup$ @EverydayAstronaut that would be surface ice sliding downhill, continuously replenished by snowfall which came from our liquid water oceans. I think you are talking here about buried, subsurface water left over from some billions of years ago. I'm pretty sure it's found a stable place now and isn't going anywhere. $\endgroup$
    – uhoh
    Commented Jan 9, 2019 at 5:26
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    $\begingroup$ @uhoh I agree on that $\endgroup$
    – Everyday Astronaut
    Commented Jan 10, 2019 at 5:39

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