APOD 4.8

May 15, 2012: All the Water on Planet Earth

     Even though we tend to think that there is a lot of water on Earth (since 70 percent of Earth's surface is covered by ocean), there actually is not that much, as this photo demonstrates.  The oceans are very shallow in comparison to Earth's radius.  If all of the water on Earth were bunched up into a concentrated point, the sphere of water would only have a radius of 700 kilometers which is less than half the radius of our moon.  We are unsure if there is water under Earth's surface.