Nights on Mars are shrouded in icy fog that turns to scattered precipitation, according to a new study of weather near the red planet's north pole, wrote National Geographic News online April 4:

The finding marks the first time that fog has been directly observed on the neighbouring world, adding to evidence that modern Mars experiences a type of ongoing water cycle akin to Earth's.

"Because the atmosphere is so thin on Mars, there is nothing to keep in the heat overnight, so the ground cools off very quickly," said study co-author John Moores, a [n NSERC post doctoral fellow and] planetary scientist at York University [Faculty of Science & Engineering].

"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 vapour 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 snow-like 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.

"Because we have the fog," Moores said, "that means that there is a reservoir of water [in the atmosphere] to interact with subsurface water on a daily basis."

The Martian-fog study was published in the Feb. 25 issue of Geophysical Research Letters.

Moores is also a member of the Centre for Research in Earth & Space Science (CRESS), which has had a significant role in the Mars-Phoenix lander mission.

Posted by Elizabeth Monier-Williams, research communications officer, with files courtesy of YFile– York University’s daily e-bulletin.