January 25, 2013
Spring Carbon Dioxide Thaw On Mars Creates Geologic Changes
[ Watch the Video: Mars Dry Ice and Dunes ]
April Flowers for redOrbit.com - Your Universe OnlineA new study, led by the Planetary Science Institute's Senior Scientists Candice Hansen, shows that the spring thaw on Mars leads to a variety of geologic changes on the planet's surface.
Frozen carbon dioxide, also known as dry ice, is deposited on the dunes surrounding the north pole's permanent water ice polar cap. In the spring, as it begins to sublimate, or change directly from a solid to a gas, the gas erodes and destabilizes the sand of the dunes.
“It´s an amazingly dynamic process,” said Hansen. “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.”
The exotic spring phenomena on Mars are described by Hansen and her team in three associated articles recently published in the journal Icarus. The team made observations from the High Resolution Imaging Science Experiment (HiRISE) camera and the infrared spectrometer (CRISM) on the Mars Reconnaissance Orbiter, which have provided a rich data set that now covers three spring seasons in the northern hemisphere.
In the first paper, the researchers use three years of data to compile reports on the sequence and variety of changes that take place over the spring. These include outbursts of gas carrying sand, polygonal cracking of the ice on the dunes, sandfalls down the slipface of the dunes, and dark fans of sand propelled out onto the ice. Channels are eroded into the dunes by gas escaping from under the seasonal layer of dry ice, not unlike the erosion that carves more permanent "spider" channels in the southern hemisphere's polar region.
Results from analyses of HiRISE images from a dozen different locations inside the area of northern polar shifting sand dunes make up the second paper. These locations are at similar latitudes but differing latitudes around the northern pole. The locations range from inside the polar ice trough to outside, from near the polar cap scarp to far away; despite the differences, all the locations follow similar trends during the spring sublimation phase. The locations experience a brightening phase, they all develop dark streaks, blotches and linear cracks in the ice, and all locations develop wind-modified fan deposits at similar times.
The third paper concerns CRISM data, which shows the variability of the composition of the seasonal ice cap in the spring. The dry ice is coated by water ice frost at some times, which is blown around on top of the dry ice.