                        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.

                               2026 January 20
    A big ball that is mostly yellow is shown. The ball has many circular
     and irregular regions that are different colors, typically brown or
   olive green. Please see the explanation for more detailed information.

                              Io in True Color
                  Image Credit: NASA, JPL, Galileo Project

   Explanation: The strangest moon in the Solar System is bright yellow.
   The featured picture, an attempt to show how Io would appear in the
   "true colors" perceptible to the average human eye, was taken in 1999
   July by the Galileo spacecraft that orbited Jupiter from 1995 to 2003.
   Io's colors derive from sulfur and molten silicate rock. The unusual
   surface of Io is kept very young by its system of active volcanoes. The
   intense tidal gravity of Jupiter stretches Io and damps wobbles caused
   by Jupiter's other Galilean moons. The resulting friction greatly heats
   Io's interior, causing molten rock to explode through the surface. Io's
   volcanoes are so active that they are effectively turning the whole
   moon inside out. Some of Io's volcanic lava is so hot it glows in the
   dark.

                       Tomorrow's picture: open space
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
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                      A service of: ASD at NASA / GSFC,
                           NASA Science Activation
                             & Michigan Tech. U.

