June 21, 2012
Snow On Mars Size Of Red Blood Cells
Lee Rannals for redOrbit.com
It snows on Mars, but it´s a little alien to what you see in places like Vail, Colorado here on Earth. The snow is actually made up of frozen crystals of carbon dioxide about the size of red blood cells, according to new research.
Most of Mars' atmosphere is made up of carbon dioxide (CO2), so during the winter months the poles get so cold that gas condenses and forms tiny particles of snow.
MIT researchers decided to use science to calculate the size of the snow particles in the clouds and at the Martian poles.
The group determined the snow particles in the south are slightly smaller than those found up in the north pole, but they are both about as small as a red blood cell.
The team didn't use some humungous microscope to reach their findings, but instead analyzed data like temperature and pressure profiles taken by the Mars Reconnaissance Orbiter (MRO) every 30 seconds over the course of five Martian years.
The MIT scientists also analyzed the data from the Mars Global Surveyor's (MGS) laser altimeter, which measure the topography of the Red Planet.
Throughout the course of a Martian year, the researchers found that it gets colder and darker from fall to winter, and snow clouds expand from Mars' poles toward its equator. The snow extends down to about halfway to the equator before shrinking toward the poles as winter turns to spring.
Using data from MRO, the team was able to see where and when conditions would allow carbon dioxide cloud particles to form.
MGS' laser altimeter would send laser pulses that bounced back to the spacecraft, and every now and then, the instrument picked up a strange signal and reflected off a high point above the planet's surface.
Graduate student Renyu Hu, who worked with Kerri Cahoy, the Boeing Career Development Assistant Professor of Aeronautics and Astronautics at MIT, analyzed the cloud returns from MGS to find evidence to confirm carbon dioxide condensation.
Hu would try and match the laser data with concurrent data on local temperature and pressure, and found in 11 instances that conditions were good for CO2 to condense.
In order to estimate the total mass of carbon dioxide snow deposited at the poles, Hu used earlier measurements of seasonal variations in the Martian gravitational field.
Hu was able to figure out the number of snow particles in a given volume of snow cover, which helped him determine the size of the particles. The snow particles in the north pole reached to a range of 8 to 22 microns, while particles in the south were between 4 to 13 microns.
“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.”
So why doesn't the Earth have CO2 snow? Well, Cahoy told redOrbit in an email why exactly that is something we do not have to worry about.
"Fortunately Earth is too warm for CO2 to condense into snow during the seasonal cycle," she told redOrbit. "If it got cold enough to snow CO2, all our water would have already frozen out of the atmosphere. On Earth, we see 'dry ice' CO2 in science class and sometimes even in the dance floor. It sublimates really fast because it's so warm. "
The team's research could lead to other understandings about planets and exoplanets in the Universe.
"Understanding more about carbon dioxide on Mars not only tells us more about how weather on Mars works today, but helps us understand more about the behavior of important gases, like CO2, in lower pressure and temperature conditions than we see on Earth," Cahoy told redOrbit. "How many other planets, exoplanets, might be out there walking the fine line between runaway greenhouse and atmospheric escape like Earth? There is so much yet to explore."