NASA Mars Lander sees falling snow

After studying vast libraries of data from NASA’s Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO), an MIT research team found some interesting facts about Martian snow.

For example, the group found that snow particles around the south pole are slightly smaller than snow around the north pole, with particles at both poles being the size of a red blood cell.

Unlike our water-based snow, the particles on Mars are carbon dioxide-based frozen crystals.  Because most of Martian atmosphere is composed of carbon dioxide and because the poles get so cold in winter, the gas condenses to form tiny particles of snow in the air.

“These are very fine particles, not big flakes, “ reports Keri Cahoy, Boeing Career Development Assistant Professor of Aeronautics and Astronautics at MIT.  Were the particles to eventually fall and settle on the Martian surface,” she continued, “you would probably see it as fog because they’re so small.”

During the course of a 687-day winter, the team found that snow clouds expand from the planet’s poles toward its equator as it gets darker and colder from fall to winter.  As winter turns to spring, the snow stretches halfway to the equator before shrinking back toward the poles.

Graduate student Renyu Hu, lead author of the study, used measurements of seasonal variations in the Martian gravitational field to estimate the total mass of carbon dioxide deposited at the two poles.  As snow piles up at the poles each winter, the planet’s gravitational field changes slightly.  The researchers determined the total mass of snow at the poles by analyzing the gravitational difference from season to season.

Using the total mass, Hu calculated the number of snow particles in a given volume of snow cover.  From that data, he determined the size of the particles:  At the north pole, molecules of condensed carbon dioxide ranged from 8 to 22 microns; at the south pole particles measured 4 to 13 microns.

“For the first time, using only spacecraft data, we really revealed this phenomenon on Mars,” said Hu.

“Since carbon dioxide makes up most of the Martian climate, understanding how it behaves on the planet will help scientist understand Mars’ overall climate,” observed Paul Hayne, a postdoc in planetary sciences at California Institute of Technology.

“The big-picture question this addresses is how the seasonal ice caps on Mars form,” says Hayne, who wasn’t involved in the research.  “The ice could be freezing directly on the surface, or forming as snow particles in the atmosphere and snowing down on the surface . . . this work seems to show that at least in some cases, it’s snowfall rather than direct ice deposition.  That’s been suspected for a long time, but this may be the strongest evidence.”

“It’s neat to think that we’ve had spacecraft on or around Mars for over 10 years, and we have all these great datasets,” Cahoy said.  “If you put different pieces of them together, you can learn something new just from the data.”

Sources:  Discovery News  June 19, 2012       MITnews  June 19, 2012    Study published in the Journal of Geophysical Research


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