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.

                                2020 April 13

                     A Sailing Stone across Death Valley
                          Image Credit: Keith Burke

   Explanation: How did this big rock end up on this strange terrain? One
   of the more unusual places here on Earth occurs inside Death Valley,
   California, USA. There a dried lakebed named Racetrack Playa exists
   that is almost perfectly flat, with the odd exception of some very
   large stones, one of which is pictured here in April of 2019 beneath a
   dark, Milky-Way filled sky. Now the flatness and texture of large playa
   like Racetrack are fascinating but not scientifically puzzling -- they
   are caused by mud flowing, drying, and cracking after a heavy rain.
   Only recently, however, has a viable scientific hypothesis been given
   to explain how heavy sailing stones end up near the middle of such a
   large flat surface. Unfortunately, as frequently happens in science, a
   seemingly surreal problem ends up having a relatively mundane solution.
   It turns out that in winter thin ice sheets form, and winds push ice
   sections laden with even heavy rocks across the temporarily slick playa
   when sunlight melts the ice.

                     Tomorrow's picture: garbled galaxy
     __________________________________________________________________

       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