-A thin atmosphere is compensated by huge diurnal temperatures.
THe long time quest for water on Mars has been resolved for some time, there is some, but it may be easier to find huge permafrost lakes by simply looking at the horizon line. Mars Permafrost, should be similar to Arctic permafrost, just as much as Arctic sea ice. Permafrost leaves a drier interface than water, but unlike water, ice is an insulator, like permafrost. In the Mars under shallow rock permafrost, the ground temperature should be colder than with thick dry rock layers, rapid conduction sun forced diurnal atmospheric inversions are a feature found with sea ice, permafrost does the same. Martian atmosphere is 100 times thinner than on Earth, however there is one. Where there is an atmosphere there is atmospheric refraction. One must observe there more carefully.
To prove this, one of the rovers must take pictures at 3 hours intervals after Local Apparent Midnight and Noon, without moving at all. The same pictures will show a different horizon line something like: