Scientists say the biggest moon in the solar system has a subsurface ocean

For decades, scientists have thought that under the surface of Jupiter's moon Ganymede there lies a salty ocean. Now, with help from the Hubble Telescope, they have been able to prove it.

"The solar system is now looking like a pretty soggy place," Jim Green, director of planetary science at NASA, told the Los Angeles Times. "The more we look at individual moons, the more we see that water is really in enormous abundance." Ganymede is the largest moon in the solar system, and the only one with its own magnetic field. It is also influenced by Jupiter's magnetic field, and head researcher Joachim Saur of the University of Cologne in Germany determined that shifts in Jupiter's magnetic field would affect the position of auroras in the moon's atmosphere differently if there were a subsurface ocean.

Computer models showed that if Ganymede did not have an ocean, the auroras would rock 6 degrees over 10 hours, and if there was an ocean, it would reduce the rocking to 2 degrees. After looking at measurements taken from the Hubble Telescope in 2010 and 2011, Saur saw the auroras move just 2 degrees over a seven-hour period. "We ran more than 100 models on supercomputers with with different parameters, but every time we got the same result," Saur said. "If you add an ocean it reduces the rock to 2 degrees."

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