CO2 snow on Mars

(News from Mars that isn’t Curiosity related!)  New data from the Mars Reconnaissance Orbiter provides firm evidence of carbon dioxide snow falling on the south pole of Mars. The atmosphere of Mars is about 95% CO2 and it has long been known that in the winter time CO2 freezes directly out of the atmosphere onto the residual polar ice caps.  But snow??

South polar residual cap of Mars, taken in April 2000 by the Mars Global Surveyor. The summer-time surface ice is mostly frozen carbon dioxide and the southern residual pole is about 400 km in size. (Credit: NASA/JPL/Malin Space Science Systems)

Paul Hayne of NASA JPL and collaborators have for the first time detected CO2 ice clouds that are thick enough to produce snow that would fall and accumulate on the surface.  Using infrared observations from the Mars Climate Sounder on the Mars Reconnaissance Orbiter from the southern Martian winter of 2006-2007, the team studied a number of “cold spots”, which are regions of anomalously low infrared brightness temperatures.  They found a large CO2 cloud about 500 km in diameter that persisted over the south polar cap throughout the winter, as well as a number of smaller, shorter-lived CO2  ice clouds at latitudes between 70 and 80 degrees.  The Mars Climate Sounder measures optical and infrared radiation from  directly overhead as well as “sideways” (by looking towards the Martian horizon from orbit) to provide information about the temperature, pressure, particles and gases in the atmosphere.

Infrared measurements by the Mars Climate Sounder on the Mars Reconnaissance Orbiter shows the size distribution of carbon dioxide ice particle deposits thought to have formed by snowfall over the south pole of Mars. (Credit: NASA/JPL-Caltech)

The authors argue that the CO2 ice particles in the clouds are large enough to fall to the ground as snow over the lifetime of the cloud.  The sideways views of the clouds also show that the CO2 ice particles extend all the way to the surface.  These new results suggest that snowfall at the south pole likely builds up the extended winter polar ice cap.

For more details, see

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