**By Duncan Geere, Wired UKA team of exometeorologists at MIT have calculated the size of the snowflakes that fall onto the polar regions of Mars in its winter, and it turns out that they're pretty tiny.

[partner id="wireduk"] Mars' weak atmosphere is comprised almost entirely of carbon dioxide, and during the chilly -87C winters on the red planet, it gets cold enough for particles of snow to form. Except that it's not snow as we know it, which is made of water crystals. Instead, it's dry ice – frozen crystals of carbon dioxide.

Using data from orbiting spacecraft, MIT researchers found that the crystals are about the size of a red blood cell – eight to 22 micrometers across – in the northern hemisphere and a smaller four to 13 micrometers across in the southern hemisphere. "These are very fine particles, not big flakes," said Kerri Cahoy, who worked on the project, in a press release, adding that if you were standing in a Martian blizzard, "you would probably see it as a fog, because they're so small."

To work out how big the particles are, the team first estimated the mass of snow deposited at both poles by measuring tiny changes in the planet's gravitational field over the seasons. Using this mass, and physical characteristics of carbon dioxide crystals, the team was able to determine the number of snow particles in a given volume of snow cover, and from there the dimensions of the particles.

"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."

The research addresses the question of how Mars' ice caps form. Over the course of a 687-day-long Martian year, snow clouds can stretch half-way to the equator, before shrinking back again as winter recedes. Since carbon dioxide makes up almost the entirety of the planet's atmosphere, it's hoped that it could shed light on Mars' climate – something that would be crucial if humans were to ever settle on the planet.

The research was funded by the Radio Science Gravity investigation of the NASA Mars Reconnaissance Orbiter mission.

Image: MSSS/JPL/NASA

Source: Wired UK

Image: MSSS, JPL, Nasa