Spring is approaching us here in the northern hemisphere on Earth once again, and we are experiencing the annual thaw of the winter ice. Spring is approaching the northern hemisphere of Mars as well, and with it comes the thaw of carbon dioxide ice. Some of that dry ice sits at the tops of cliffs, and when it thaws it dislodges the material there. The rock and debris on Mars then does the same thing it would do on Earth: it falls. Fast. And when it does, you get this slice of Martian awesomeness:
Holy scarp! That's another avalanche on Mars caught in the act by the HiRISE camera on Mars Reconnaissance Orbiter. I say another, because a few others have been seen, including this spectacular one two years ago, and lots of older ones that left their marks on the Red Planet's surface. This one is amazing! You can see the debris falling down the cliff's edge (the top of the cliff is to the bottom left of the image, and we're looking almost straight down the cliff's face) and then creating a plume of dust at the bottom, hundreds of meters below. When HiRISE took this image, the slide couldn't have been more than a minute old. If you look at the higher-res image (click the image above to embiggen) you can see that there have been a lot of avalanches here in the past, too. The bottom of the cliff has lots of material clearly deposited by fast-moving falling debris. To be honest, it's not completely sure that the sublimation (the change from solid directly to gas) of carbon dioxide is causing these avalanches, but it does seem the most likely explanation. Whether it's dry ice or not, what this shows us directly is that Mars is still an active place. Certainly the surface is undergoing continual (if small scale) modification, with avalanches, meteor strikes, and other processes still occurring even, literally, today. Mars is a very, very cool place. If you want to learn more, check out the HiRISE blog, which always has great stuff, including explanations of these extraterrestrial rockslides. And when you read about Mars and our exploration of it, remember this: it is an entire world, worthy of our attempts to understand it. And that is one of the grandest things we humans ever do.