Last year I wrote a post for the Heli-Ski blog, musing about the potential of snowboarding and skiing on the dry ice snow that falls on Mars. I had fun writing the post, but I must admit I felt a bit like the ski bum who’d had a few too many talking about some absurd snow-riding mission. (Not that there's anything wrong with that!)
Then, when Jason Semenek at CMH Heli-Skiing sent me a link from the NASA website with a clip of Serina Diniega, a Systems Engineer at the Jet Propulsion Laboratory, having similar ideas, complete with animation of an astronaut snowboarding on the Marian dunes, I suddenly felt like I wasn’t so far out after all. She concluded:
“I’m looking forward to the day when astronauts can engage in a whole new era of extreme sports – when they can snowboard down a carbon dioxide-covered dune on a cushion of carbon dioxide and just shoot right down those slopes. It would be amazing.”
Of course Ms. Diniega has a lot better science to back up her musings.
While I imagined riding the dry ice snow that falls on the Martian poles during the winter, Ms. Diniega was explaining the mysterious, snowboard-like tracks seen on the slopes of Martian sand dunes:
To test a theory that the tracks were caused by the motion of dry ice blocks melting from the ridges of the dunes, a group of scientists took blocks of water ice, dry ice, and wood to a sand dune on Earth. What they found was surprising, but backed up the theory of dry ice causing the tracks on Mars.
Unsurprisingly, the wood block, acting as a control group, slid until sand built up in front of it, and then stopped. The water ice acted much the same, stopping after only a few feet of travel. The dry ice block, surprisingly, slid smoothly and quickly all the way to the bottom of the dune.
On the steepest dunes – 33 degrees, the steepest angle sand can sit on in repose – the results were surprising. When they repeated the experiment on dunes as low angle as 6 degrees, the dry ice still slid all the way to the bottom of the dune. So what was happening?
According to the JPL scientists, what happens is that the sand was warmer than the dry ice, so it causes melting on the bottom of the solid ice. This forms a cushion of gas that allows the dry ice to slide along on an air cushion, thus travelling along the sandy surface with much reduced friction.
I must admit, it got me musing again. Not so much about snowboarding on Mars this time, but about riding sand dunes here on earth with a snowboard tuned, not with P-Tex and wax, but with dry ice. Ripping sand dunes on a board riding a cushion of air? Now we’re talkin’. Besides, the lift ticket would be a lot cheaper than riding on Mars…
Screenshot of dry ice tracks and video from NASA's multimedia gallery.