Auroras wrapped around Jupiter’s moon Ganymede, the solar system’s largest moon, have confirmed that a salty ocean hides beneath the world’s surface.

The observations, made with the Hubble Space Telescope, add Ganymede to a long list of places in the solar system where water is abundant. They also suggest a way for scientists to remotely look for water on distant exoplanets. Described today in the Journal of Geophysical ResearchDescribed today in the Journal of Geophysical Research, the results are a slick observational feat, and the first time auroras have been used to remotely peer inside a world.

“We aren’t at Jupiter. Hubble is at the Earth, and yet it can probe the internal structure of this