There are snowflakes on Mars.
Although they're not the type you can stick out your tongue and lick, as Massachusetts Institute of Technology researchers have found that the carbon dioxide snow particles are roughly the size of a human red blood cell.
These are very fine particles, not big flakes, Kerri Cahoy, an assistant professor of aeronautics and astronautics at MIT, said.
To the naked eye, Mars snowflakes would resemble a fog, Cahoy said, because they're so small.
For the first time, using only spacecraft data, we really revealed this phenomenon on Mars, said Renya Hu, a graduate student who worked with Cahoy and MIT geophysics professor, Maria Zuber.
The MIT researchers studied the Martian atmosphere at the planet's poles, which become cold enough in winter to freeze alcohol and to condense the carbon dioxide gas into tiny snowlike particles that are about the size of a human red blood cell.
Because Mars landers so far are incapable of surviving harsh conditions at the poles, according to National Geographic, the MIT researchers came to their conclusion using nine years' worth of data (five years in Mars time), from the Mars Global Surveyor and Mars Reconnaissance Orbiter, among other resources.
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.
Mars snowflakes were larger in the northern pole, where carbon dioxide ranged from 8 to 22 microns. Snow particles in the south were measured to be between 4 and 13 microns.
A human red blood cell is about 6 to 8 microns wide, according to National Geographic.
The findings may help future researchers understand the Mars climate, according to Paul Hayne, a post-doctoral student in planetary sciences, at the California Institute of Technology. Carbon dioxide makes up most of the Red Planet's atmosphere.
The big-picture question this addresses is how the seasonal ice caps on Mars form, said Hayne, who was not involved in the research. The ice could be freezing directly at 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.
The size of Mars snowflakes may also be helpful in understanding the properties of dust in the Martian atmosphere, according to Hu.
Hu said the research leads to questions about dust particles, which are needed for snow to form as carbon dioxide needs something to condense.
What kinds of dust do you need to have this kind of condensation? Hu asks. Do you need tiny dust particles? Do you need a water coating around that dust to facilitate cloud formation?