In 2008, we learned from the Phoenix Mars lander that it snows in Mars northern hemisphere — perhaps quite regularly – from clouds made of water vapor. But now, Mars Reconnaissance Orbiter data has revealed the clearest evidence yet of carbon-dioxide snowfalls on Mars. Scientists say this is the only known example of carbon-dioxide snow falling anywhere in our solar system.“These are the first definitive detections of carbon-dioxide snow clouds,” said Paul Hayne from the Jet Propulsion Laboratory, lead author of a new study published in the Journal of Geophysical Research. “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.”
Scientists have known for decades that carbon-dioxide exists in ice in Mars’ seasonal and permanent southern polar caps. Frozen carbon dioxide, sometimes called “dry ice” here on Earth, requires temperatures of about -125 Celsius (- 193 degrees Fahrenheit), which is much colder than needed for freezing water.
Even though we like to think Mars is a lot like Earth, findings like this remind us that Mars is indeed quite different. But just as the water-based snow falls during the winter in Mars’ northern hemisphere, the CO2 snowfalls occurred from clouds around the Red Planet’s south pole during winter in the southern hemisphere.
― Elvis Telecom, Friday, 14 September 2012 04:51 (eleven years ago) link