NASA’s Mars Reconnaissance Orbiter has provided scientists with the clearest evidence to date of carbon-dioxide snowfalls on Mars, revealing the only known example of carbon-dioxide snow falling anywhere in our solar system.
Frozen carbon-dioxide is better known here on Earth as dry ice, and requires temperatures of around minus minus 125 Celsius (193 degrees Fahrenheit), much, much colder than what is needed to freeze water.
The report of this discovery is to be published in the Journal of Geophysical Research.
“These are the first definitive detections of carbon-dioxide snow clouds,” said the report’s lead author, Paul Hayne of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We firmly establish the clouds are composed of carbon dioxide — flakes of Martian air — and they are thick enough to result in snowfall accumulation at the surface.”
The Mars Reconnaissance Orbiter is a multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit. The Orbiter detected the snowfalls in clouds around Mars’ south pole in winter, though the presence of carbon-dioxide ice in Mars’ seasonal and residual southern polar cabs has been known for decades. NASA’s Phoenix Lander mission in 2008, for example, detected falling water-ice snow on northern portion of the planet. Mars’ south pole is the only location on the planet where frozen carbon dioxide persists on the surface year round.
Hayne and his six co-authors analysed data taken using the Mars Climate Sounder, one of six instruments on board the Mars Reconnaissance Orbiter. The Sounder looked at clouds from directly above and side on, recording brightness in nine wavebands of visible and infrared light as a means to examine particles and gases in the Martian atmosphere.
The results revealed information detailing temperature, particle sizes, and their concentrations.
“One line of evidence for snow is that the carbon-dioxide ice particles in the clouds are large enough to fall to the ground during the lifespan of the clouds,” co-author David Kass of JPL said. “Another comes from observations when the instrument is pointed toward the horizon, instead of down at the surface. The infrared spectra signature of the clouds viewed from this angle is clearly carbon-dioxide ice particles and they extend to the surface. By observing this way, the Mars Climate Sounder is able to distinguish the particles in the atmosphere from the dry ice on the surface.”
“The finding of snowfall could mean that the type of deposition — snow or frost — is somehow linked to the year-to-year preservation of the residual cap,” Hayne said.
Source: NASA Jet Propulsion Laboratory