                        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.

                              2025 September 1
   A dark spherical body is shown that has many light craters. Please see
               the explanation for more detailed information.

                      Callisto: Dirty Battered Iceball
   Image Credit: NASA, JPL-Caltech, Voyager 2; Processing & License: Kevin
                                  M. Gill;

   Explanation: Its surface is the most densely cratered in the Solar
   System -- but what's inside? Jupiter's moon Callisto is a battered ball
   of dirty ice that is larger than the planet Mercury. It was visited by
   NASA's Galileo spacecraft in the 1990s and 2000s, but the recently
   reprocessed featured image is from a flyby of NASA's Voyager 2 in 1979.
   The moon would appear darker if it weren't for the tapestry of
   light-colored fractured surface ice created by eons of impacts. The
   interior of Callisto is potentially even more interesting because
   therein might lie an internal layer of liquid water. This potential
   underground sea is a candidate to harbor life -- similar with sister
   moons Europa and Ganymede. Callisto is slightly larger than Luna,
   Earth's Moon, but because of its high ice content is slightly less
   massive. ESA's JUICE and NASA's Europa Clipper missions are now headed
   out to Jupiter to better investigate its largest moons.

                    Tomorrow's picture: flaming sky horse
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
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                           NASA Science Activation
                             & Michigan Tech. U.

