Details of Snowfall on Mars Explained

The planetMars conjures images of red rocks and arid, dusty plains, but as NASA's PhoenixMars Lander showed last year, it snows on Mars.

Thestationary robot observed icecrystals falling to the martian surface near the end of its 5-month missionin the arctic Vastitas Borealis plains last year. Today, scientists detail thisfinding and others in a set of four papers in the journal Science. Theresearch could help shed light on the past and present action of water on themartian surface and characterize the potential habitability of the red planet.

Phoenix landed on the red planet on May 25,2008, with a mission to dig up and analyze samples of Martian dirt, confirm theexistence of a subsurface layer of water ice and observe the weather at its farnorthern locale.

Cirrusclouds?

Spacecraftorbiting Mars had previously detected clouds high up in the Martian atmosphereand low-level "ice fog," "but they've never seen precipitation,"said James Whiteway of York University in Canada, the lead scientist for Phoenix's meteorological instruments.

From itsvantage point on the Martian surface, Phoenix used its LIDAR (light detectionand ranging) instrument, supplied by the Canadian Space Agency, to emit laserpulses upward into the atmosphere and detectedclouds and precipitation above its landing site.

The cloudswere low-level, wispy clouds made up of ice crystals, similar to the cirrusclouds that form over the Earth's polar regions in the winter. Whiteway alsolikened them to the thin clouds jet planes fly through high in the Earth'satmosphere.

"Thethin, wispy clouds up there have a similar water content," he told SPACE.com.

The cloudsdidn't begin forming until around sol (Martian day) 80 or 90 of the mission,when air temperatures were cool enough for water vapor in the atmosphere tocondense out, Whiteway explained.

As themission wore on, the clouds became thicker, lower to the ground and persistedfor longer.

?andsnow

The snowdidn't come until close to the end of the mission. It too is similar to thesnow that falls to the ground at Earth'spoles, sometimes called "diamond dust." Whiteway describes it as"ice crystals sparkling in the air."

The snowwasn't enough to build a snowmartian with, however, amounting to only a couplemicrometers (there are 1,000 micrometers in a millimeter) a day if it wasmelted on the surface, Whiteway said.

Theobservations show that "precipitation is a component of the hydrologiccycle" on Mars, which was not suspected before the Phoenix mission,Whiteway said.

How thefinding might impact our understanding of the global Mars water cycle ? bothnow and in the distant past, when the planet is suspected to have been warmerand wetter ? is not yet known.

The newinformation can be used to modify Martian climate models, which currently don'tfeature these newly discovered clouds and precipitation, "and then we'llsee what the implications are," Whiteway said.

• Very Short Movie: The Clouds of Mars
• Earth vs. Mars: Polar Opposites
• Images: Phoenix on Mars