Fog on Mars

This report on a newly-released analysis of data from the Phoenix lander pretty closely describes what we had in mind for the “yardang” scene…only in reverse – Martian-Fog Study Finds Thick Haze, “Diamond Dust”:

“Heat from the air is lost to the ground, so the air close to the ground gets colder, and as that pocket of [cold] air gets larger,” more water vapor in the atmosphere condenses into ice crystals, and the fog gets thicker, Moores said.

“The fog starts closer to the ground and rises in height over time, so the cloud gets thicker and thicker and higher and higher as the night goes on,” he added.

Eventually the icy haze begins to shower the ground with a light sprinkling of snowlike particles. The shower is not quite snowfall, the scientists say, but is perhaps more akin to the “diamond dust” that falls from the skies on some cold nights in Earth’s Arctic regions.

Some 0.0001 inch (2.5 micrometers) of frost coats the Martian surface by the time the sun begins to rise in the morning. That icy layer then sublimates—turns directly from a solid to a gas.

In our case, the resulting frost at first sublimates into a fog as sunlight hits it, then rapidly dissipates. It may be a bit of literary license (or not — there’s no saying that what we described doesn’t happen), but it’s not far off from observed reality.