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    Dry Ice Surfs Martian Dunes

    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." (NASA/JPL-Caltech/Univ. of Arizona)
    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." (NASA/JPL-Caltech/Univ. of Arizona)

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    VOA News
    Some of the mysterious gullies seen on Martian sand dunes may be formed by sliding blocks of carbon dioxide, also known as dry ice, according to a NASA research report.

    "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."

    According to the research, the so-called linear gullies all have a near constant width of a few meters, with raised banks on the sides. The reason the gullies don’t appear to be formed by liquid is that there are no deposits of debris at the bottom of their lower edge. Instead, NASA says, they have pits.

    "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 NASA's Mars Reconnaissance Orbiter (MRO) led scientists to the theory, which in turn led to performing experiments on sand dunes in Utah and California.

    During the experiments on Earth, scientists found that dry ice forms a “lubricating layer” of gaseous carbon dioxide that allowed the chunks to glide down the dunes even when the slope was shallow. The chunks also pushed aside sand into small levees.

    "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," said report co-author Candice Hansen of the Planetary Science Institute in Tucson, Arizona. "Just because this dry-ice hypothesis looks like a good explanation for one type doesn't mean it applies to others."

    Images taken during the Martian winter show the gullies covered by frozen carbon dioxide frost, while images taken early in the Martian spring reveal the gullies. In some of the images, NASA said there appear to be bright object in the gullies. Scientists believe they are pieces of dry ice that have fallen from higher areas of the dunes. The pits at the bottom of the gullies, NASA believes, are caused by the evaporation of the ice chunks after they’ve come to rest.

    "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."

    Here's a video about the gullies:


    Embedded video from
    NASA Jet Propulsion Laboratory California Institute of Technology

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