Previous research has offered circumstantial evidence that Ganymede, the largest moon in the solar system, contains more water than all of Earth's oceans put together. However, temperatures there are so cold that the water on the surface is frozen solid. Also, Ganymede ’ s ocean is thought to be 100 miles below the moon ’ s crust. This means that the water vapor discovered by Hubble is not likely to represent the evaporation of this ocean.
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