In the video below, scientists Tony Darnell, Dr. Carol Christian and Scott Lewis discuss observations of Ganymede with the Hubble Space Telescope science team.

Nearly 500 million miles from the Sun lies a moon orbiting Jupiter that is slightly larger than the planet Mercury and may contain more water than all of Earth’s oceans. Temperatures are so cold, though, that water on the surface freezes as hard as rock and the ocean lies roughly 100 miles below the crust. Nevertheless where there is water there could be life as we know it.

Identifying liquid water on other worlds – big or small – is crucial in the search for habitable planets beyond Earth. Though the presence of an ocean on Ganymede has been long-predicted based on theoretical models, NASA’s Hubble Space Telescope found the best circumstantial evidence for it.

Hubble was used to watch aurorae glowing above the moon’s icy surface. The aurorae are tied the moon’s magnetic field which descends right down to the core of Ganymede. A saline ocean would influence the dynamics of the magnetic field as it interacts with Jupiter’s own immense magnetic field that engulfs Ganymede.

Because telescopes can’t loo inside planets or moons, tracing the magnetic field through aurorae is a unique way to probe the interior of another world.

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