                        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 7
   An illustration of planet Earth is shown where the Earth is tan and has
   no water shown on its surface. In the foreground are several small blue
   spheres showing how much water is known to reside on our planet. Please
             see the explanation for more detailed information.

                        All the Water on Planet Earth
    Illustration Credit: Jack Cook, Adam Nieman, Woods Hole Oceanographic
                 Institution; Data source: Igor Shiklomanov

   Explanation: How much of planet Earth is made of water? Very little,
   actually. Although oceans of water cover about 70 percent of Earth's
   surface, these oceans are shallow compared to the Earth's radius. The
   featured illustration shows what would happen if all of the water on or
   near the surface of the Earth were bunched up into a ball. The radius
   of this ball would be only about 700 kilometers, less than half the
   radius of the Earth's Moon, but slightly larger than Saturn's moon Rhea
   which, like many moons in our outer Solar System, is mostly water ice.
   The next smallest ball depicts all of Earth's liquid fresh water, while
   the tiniest ball shows the volume of all of Earth's fresh-water lakes
   and rivers. How any of this water came to be on the Earth and whether
   any significant amount is trapped far beneath Earth's surface remain
   topics of research.

                     Tomorrow's picture: butterfly webb
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       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.

