Asked Brian Lawrence
At such cold temperatures, it does snow on Mars – NASA’s Phoenix Mars Lander detected snow falling from the Martian clouds back in September 2008. However, before the snow had a chance to reach the ground, it vaporised into streaks called virgae.
Even more-recent studies with the Mars Reconnaissance Orbiter revealed clear evidence that there are in fact carbon dioxide snow clouds. Scientists behind the study revealed that these clouds were thick enough to result in snowfall accumulation on the surface of the Red Planet. Just as water-based snowfalls occur during winter in Mars’ northern hemisphere, carbon dioxide snowfalls occur in the planet’s southern hemisphere during the south pole’s own winter.
Frozen CO2 persists in the southern region all year round, but how it got there is still a mystery.