Inside Solar System's Biggest Moon: an Ocean

Where there is water, there could be life, NASA scientists say—and they have found evidence of a vast amount of water on Ganymede, Jupiter's biggest moon and the biggest moon in the solar system. Ganymede is the only one known to have its own magnetic field, and Hubble Space Telescope researchers studied the auroras the field produces to detect a huge, salty ocean under its surface that is believed to hold more water than all the oceans on Earth, Space.com reports. The researchers believe the ocean under the planet's icy crust, which earlier research had hinted at, is 60 miles deep, more than 50 miles deeper than the deepest spot in our planet's oceans, Scientific American reports.

"The solar system is now looking like a pretty soggy place," says NASA's director of planetary science—and the method the Hubble researchers used to look inside Ganymede could detect oceans on planets far beyond our solar system, experts say. To detect water on exoplanets by monitoring auroras "may require a much larger telescope than Hubble, it may require some future space telescope, but nevertheless, it's a tool now that we didn't have prior to this work," an Association of Universities for Research in Astronomy spokeswoman tells Space.com. (Earlier this year, NASA detected signs of a subsurface ocean capable of hosting life on the solar system's biggest asteroid.)