Fluffy White Stuff Falling in the Last Place You’d Expect It

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The fluffy white stuff in question fell during the winter of 2006/2007, so it’s been a few years. And, it didn’t fall any place nearby. In fact, it didn’t even fall on Earth. Even more peculiar, it wasn’t even white fluffy stuff…at least, not as we know it.

Scientists at NASA’s Jet Propulsion Laboratory have been poring over data collected from the Mars Reconnaissance Orbiter (MRO) and have discovered snowfall, in the form of carbon dioxide snowfall, that fell to the surface of Mars six years ago (six years means a lot of data are coming from the MRO, yes?). Frozen carbon dioxide by the way, in frozen form, is as close as your local Earth supermarket’s sub-zero freezer: it’s called dry ice.

Artist’s conceptual image of the Mars Reconnaissance Orbiter in orbit around Mars. Instruments aboard the orbiter measure brightness in various wavelengths of visible and infrared light, allowing scientists to learn characteristics of the particles and gases in the Martian atmosphere. Image: Wikipedia

This is quite interesting because if you add 2 and 2 your answer will lead you to the wrong conclusion. You’d likely think that the frozen carbon dioxide “precipitated” from the Martian clouds, falling to the surface. That’s true, in a way, but since the atmosphere of Mars is up to 95% carbon dioxide, the “snow” is actually thin slices of the Martian air — it might not even need a cloud to fall from. Compare that to Earth, where our atmosphere — at least the part that makes up snow and other forms of precipitation — is only about 1% water vapor.

It remains a question as to whether the dry ice falls from clouds or whether it just freezes in mid-air near the surface. One thing’s for sure: dry ice blankets the polar caps of Mars year-round. Since dry ice needs temperatures of -193 Fahrenheit to exist (if temperatures warm, the dry ice will evaporate into a fog — the classic ingredient of the best Halloween parties and horror movies back home on Earth), it’s a safe bet that when humans finally colonize Mars we’ll need some serious cold weather gear.

What would Halloween be like without the fog of evaporating dry ice? Photo: philosophyofscience

Speaking of Earth… It’s tough this time of year to find falling snow (the frozen water vapor-type). In the Northern Hemisphere, we’re moving into winter, while the Southern Hemisphere is moving out of winter. This means the coldest temperatures are mostly confined to the far northern and far southern latitudes…and that’s where the falling snow is today. For instance, there’s a strong area of low press moving towards the western coast of Chile where temperatures in the southern city of Punta Arenas are in the low 30s (F). Currently the skies of Puntas Arenas are sunny but the approaching front will bring rain, not snow.

No snow for the U.S. – at least, not yet. However, colder temperatures are now beginning to move southward from the northern latitudes. The first day of fall (Autumnal Equinox) is this coming Saturday. Image: ImpactWeather

On the other side of the globe, temperatures in the U.S. are getting colder. It’s 38 Fahrenheit in Sioux Falls, SD. It’s 30 in Whitehorse, Yukon Territory and in Fairbanks. On the northern coast of the Sea of Okhotsk, in Magadan it’s 30 degrees as they move into their overnight hours. None of these locations have snow in their forecast. But that will change, of course, as we’re quickly moving into the colder time of year.

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