reports the three new studies, published in the journal Icarus
, were based on images of sand dunes on Mars' north polar region snapped by NASA's Mars Reconnaissance Orbiter (MRO)
spacecraft over a period of three Martian years, or about six Earth years, using its High Resolution Imaging Science Experiment
camera (HiRise). The images revealed how thawing of carbon dioxide ice, known as "dry ice," at the beginning of Martian spring in the northern hemisphere, carves grooves in the region's sand dunes (see video
reports that Candice Hansen of the Planetary Science Institute
in Tucson Arizona, lead author of the one of the studies, said: "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."
reports that the thawing begins in the underside of the ice layer in contact with warmer ground. The dry ice sublimes, that is, passes from solid state to gaseous state. As more gas is formed, pressure builds in the lower layers until cracks appear in the ice. The carbon dioxide gas is released through the cracks, breaks through to the surface, creating grooves in the dunes with hissing as the gas escapes.
The escaping gas also lifts sand which form as dark streaks or fans across the dry ice covering the dunes. The fans are erased as Martian spring progresses, and dry ice covering the sand dunes evaporates. Winds erase the grooves before the next winter commences.
Ganna Portyankina of the University of Bern in Switzerland, lead author of one of the studies, said in a statement: "It is a challenge to catch when and how those changes happen, they are so fast. That's why only now we start to see the bigger picture that both hemispheres actually tell us similar stories."