Curiosity may be roving the Martian frontier to find out just
how similar the Red Planet is to Earth, but meanwhile NASA’s
other Martian explorers are turning up evidence of just how
different our neighboring planet can be. The Mars Reconnaissance
Orbiter has returned data suggesting that it snows on Mars just
like it snows on Earth, with one key difference: On Mars, it
snows dry ice. Dry ice, which is frozen carbon dioxide rather
than solidified water, requires temperatures dipping far below
those experienced beneath Earth’s atmosphere--roughly 193
degrees below zero Fahrenheit, to be slightly more precise.
Researchers had already firmly established that clouds of carbon
dioxide exist in Mars’ southern polar region, and they had
previously found carbon-dioxide ice in the polar caps at the
Martian south pole. What they lacked was the mechanism by which
this carbon dioxide moves between cloud and ice cap--via
precipitation or simply freezing out at ground level, like
frost. And that’s what they’ve now found, t