Dry Ice "Snowboards" on Mars   
       
   June 11, 2013: NASA research indicates hunks of frozen carbon dioxide -- dry   
   ice -- may glide down some Martian sand dunes on cushions of gas similar to   
   miniature hovercraft, plowing furrows as they go.   
       
   "I have always dreamed of going to Mars," said Serina Diniega, a planetary   
   scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and lead   
   author of a report published online by the journal Icarus. "Now I dream of   
   snowboarding down a Martian sand dune on a block of dry ice."   
       
   http://www.nasa.gov/mission_pages/MRO/multimedia/pia17260.html   
       
   This image from the High Resolution Imaging Science Experiment (HiRISE) camera   
   on NASA's Mars Reconnaissance Orbiter is an example of a type called "linear   
   gullies," which may be explained by slabs of dry ice gliding down the slopes   
   of sand dunes. Image credit: NASA/JPL-Caltech/Univ. of Arizona   
       
   Researchers deduced this process could explain one enigmatic class of gullies   
   seen on Martian sand dunes by examining images from NASA's Mars Reconnaissance   
   Orbiter (MRO) and performing experiments on sand dunes in Utah and California.   
       
   The hillside grooves on Mars, called linear gullies, show relatively constant   
   width -- up to a few yards, or meters, across -- with raised banks or levees   
   along the sides. Unlike gullies caused by water flows on Earth and possibly on   
   Mars, they do not have aprons of debris at the downhill end of the gully.   
   Instead, many have pits at the downhill end.   
       
   "In debris flows, you have water carrying sediment downhill, and the material   
   eroded from the top is carried to the bottom and deposited as a fan-shaped   
   apron," said Diniega. "In the linear gullies, you're not transporting   
   material. You're carving out a groove, pushing material to the sides."   
       
   Images from MRO's High Resolution Imaging Science Experiment (HiRISE) camera   
   show sand dunes with linear gullies covered by carbon-dioxide frost during the   
   Martian winter. The location of the linear gullies is on dunes that spend the   
   Martian winter covered by carbon-dioxide frost. By comparing before-and-after   
   images from different seasons, researchers determined that the grooves are   
   formed during early spring. Some images have even caught bright objects in the   
   gullies.   
       
   http://tinyurl.com/kjh3lnp   
       
   A video from JPL shows how dry ice sliding down slopes can produce gully-like   
   furrows. Play itScientists theorize the bright objects are pieces of dry ice   
   that have broken away from points higher on the slope. According to the new   
   hypothesis, the pits could result from the blocks of dry ice completely   
   sublimating away into carbon-dioxide gas after they have stopped traveling.   
       
   "Linear gullies don't look like gullies on Earth or other gullies on Mars, and   
   this process wouldn't happen on Earth," said Diniega. "You don't get blocks of   
   dry ice on Earth unless you go buy them."   
       
   That is exactly what report co-author Candice Hansen, of the Planetary Science   
   Institute in Tucson, Ariz., did. Hansen has studied other effects of seasonal   
   carbon-dioxide ice on Mars, such as spider-shaped features that result from   
   explosive release of carbon-dioxide gas trapped beneath a sheet of dry ice as   
   the underside of the sheet thaws in spring. She suspected a role for dry ice   
   in forming linear gullies, so she bought some slabs of dry ice at a   
   supermarket and slid them down sand dunes.   
       
   That day and in several later experiments, gaseous carbon dioxide from the   
   thawing ice maintained a lubricating layer under the slab and also pushed sand   
   aside into small levees as the slabs glided down even low-angle slopes.   
       
   The outdoor tests did not simulate Martian temperature and pressure, but   
   calculations indicate the dry ice would act similarly in early Martian spring   
   where the linear gullies form. Although water ice, too, can sublimate directly   
   to gas under some Martian conditions, it would stay frozen at the temperatures   
   at which these gullies form, the researchers calculate.   
       
   "MRO is showing that Mars is a very active planet," Hansen said. "Some of the   
   processes we see on Mars are like processes on Earth, but this one is in the   
   category of uniquely Martian."   
       
   To see images of the linear gullies and obtain more information about MRO,   
   visit: http://www.nasa.gov/mro .   
       
   Credits:   
       
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More information:   
       
   Hansen also noted the dry ice "snowboarding" process could be unique to the   
   linear gullies described on Martian sand dunes. "There are a variety of   
   different types of features on Mars that sometimes get lumped together as   
   'gullies,' but they are formed by different processes," she said. "Just   
   because this dry-ice hypothesis looks like a good explanation for one type   
   doesn't mean it applies to others."   
       
   The University of Arizona Lunar and Planetary Laboratory operates the HiRISE   
   camera, which was built by Ball Aerospace & Technologies Corp. of Boulder,   
   Colo. JPL, a division of the California Institute of Technology in Pasadena,   
   manages MRO for NASA's Science Mission Directorate in Washington. Lockheed   
   Martin Space Systems, Denver, built the orbiter.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.94   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)