Apparently there is a lot more going on on the Martian surface than we thought. Sure, we're interested in all the stuff that happened there billions of years ago, but as it turns out we can observe some interesting things happening with the change of the Martian seasons each year. Frozen carbon dioxide thaws and somewhat violently creates feathery looking sand dunes in Mars' northern hemisphere.
The process happens every Martian spring. The frozen carbon dioxide — dry ice — lies in layers on the dark basalt formations below it. During the thaw, the first ice to "melt" is the layer closest to the dark and sandy surface. What is really happening is the frozen CO2 is thawing into its gaseous state and building up enormous pressure under the surface of the top ice. Eventually, the pressure causes cracks in the surface where the gas jets out, forming grooves on the surface and brining up bits of the basalt and sand with it.
Once released, the CO2 condenses, dragging the surface material back down with it. Those dark fans formed on the surface show where the CO2 landed after escaping under extreme pressure. If there's some wind, the fans can be even more pronounced and streaked.
It's a temporary display as the wind and the other layers of dry ice evaporate during the rest of the springtime activity. Fortunately it's one we can observe via a video created from images captured by the HiRISE camera on the Mars Reconnaissance Orbiter as it has orbited over six years.
Candice Hansen from the Planetary Science Institute was quoted in Space.com:
“It’s an amazingly dynamic process. We had this old paradigm that all the action on Mars was billions of years ago. Thanks to the ability to monitor changes with the Mars Reconnaissance Orbiter, one of the new paradigms is that Mars has many active processes today.”
In fact, data continuing to come back from the MRO is showing similar activity may be happening in the southern hemisphere. So it seems Mars isn't just a dusty old rock; if it can create dunes, who knows what else we'll discover about its surface?
Fortunately for us, the good people at the Jet Propulsion Laboratory at the California Institute of Technology know we love to see appearing and disappearing Martian dunes and of course, gaseous explosions, and they gladly share their findings with the world.