Snowflakes on Mars are smaller than their Earth counterparts, having roughly the same diameter as a human red blood cell, a new study reports.

Researchers analyzed observations made by two Mars-orbiting spacecraft to calculate the size of snowflakes on the Red Planet, which are composed of carbon dioxide rather than water.

"These are very fine particles, not big flakes," study co-author Kerri Cahoy, of the Massachusetts Institute of Technology in Cambridge, said in a statement. An astronaut standing among snow particles falling onto the Martian surface "would probably see it as a fog, because they’re so small," Cahoy added.

Clouds of snow hang above Mars during the planet's winter, covering its poles and reaching about halfway to the equator. The researchers studied observations of these clouds made over the last decade or so by two NASA spacecraft, the Mars Global Surveyor (MGS) and the Mars Reconnaissance Orbiter (MRO).

For example, the team looked at temperature and pressure profiles taken by MRO to determine where and when conditions would allow carbon dioxide snow particles to form. They also analyzed measurements from MGS' laser altimeter, which gauged the topography of Mars by timing how long laser pulses took to bounce back from the planet's surface. (livescience.com)