Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2021 January 6

                         Striped Sand Dunes on Mars
   Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA; Processing: Wl/odek
                                 Gl/azewski;
      Text: Alex R. Howe (NASA/USRA, Reader's History of SciFi Podcast)

   Explanation: Why are these sand dunes on Mars striped? No one is sure.
   The featured image shows striped dunes in Kunowsky Crater on Mars,
   photographed recently with the Mars Reconnaissance Orbiter's HiRISE
   Camera. Many Martian dunes are known to be covered unevenly with carbon
   dioxide (dry ice) frost, creating patterns of light and dark areas.
   Carbon dioxide doesn't melt, but sublimates, turning directly into a
   gas. Carbon dioxide is also a greenhouse material even as a solid, so
   it can trap heat under the ice and sublimate from the bottom up,
   causing geyser-like eruptions. During Martian spring, these eruptions
   can cause a pattern of dark defrosting spots, where the darker sand is
   exposed. The featured image, though, was taken during Martian autumn,
   when the weather is getting colder - making these stripes particularly
   puzzling. One hypothesis is that they are caused by cracks in the ice
   that form from weaker eruptions or thermal stress as part of the
   day-night cycle, but research continues. Watching these dunes and
   others through more Martian seasons may give us more clues to solve
   this mystery.

                       Tomorrow's picture: open space
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
                NASA Web Privacy Policy and Important Notices
                      A service of: ASD at NASA / GSFC
                             & Michigan Tech. U.

--- hpt/lnx 1.9.0