Looking for water? Try Jupiter’s largest moon.

In the search for extraterrestrial life within our solar system, Mars has tended to dominate the conversation. But there may be more promising destinations a little further afield. For decades, scientists have suspected that several of the moons of Jupiter have one major advantage: Liquid water, and lots of it, deep below their icy surfaces.

Now, a pair of discoveries made in the last three weeks has further confirmed the presence of an ocean beneath the surface of Ganymede, the biggest moon orbiting Jupiter and the largest satellite in the solar system.

The challenge scientists face when trying to understand and measure an internal ocean is that by definition, such a body of water is not visible through any lens. Researchers must instead find ways to make indirect observations. One team lead by Joachim Saur, a professor of geophysics at the University of Cologne in Germany, found an innovative way to measure Ganymede’s ocean — by study’s the moon’s auroras.

“We used the Hubble Space Telescope to monitor the aurora because you cannot directly look into the moon, so we use something that gives us signs about the interior…we found it’s a massive reservoir of water, likely an a ocean with a hundred kilometers of width,” Saur says.

Saur’s paper was published on March 12. Then, eight days later, a separate team lead by scientist Paul Schenk of the Lunar and Planetary Institute in Houston revealed an unexpected finding that further confirmed the existence of water below the surface of Ganymede.

Like someone you know who has grown too fond of beer in the their 30s, Ganymede has a giant bulge across its middle.

As Nadia Drake explains for National Geographic, scientists believe that the 375-mile-wide and 2-mile-high bulge was originally part of a thick concentration of ice at one of the moon’s poles. As the ice grew heavier, it began to drift, until eventually, it ended up near the equator.

A phenomenon known as “true polar drift,” it could only happen on the moon if the ice on the surface were sitting atop something more fluid, which in Ganymede’s case, scientists suspect is a global ocean.

The belief was that water on Ganymede is part of what lead the European Space Agency to plan to send a probe to the moon, the the Jupiter Icy moons Explorer (JUICE), which is set to launch in 2022. In terms of the known ingredients for life, Ganymede checks off a few boxes: water, oxygen, minerals and a heat source, courtesy of the strong tides of Jupiter. There is no direct sign of life on Ganymede, but researchers think its worth a closer look.

“In the search for life outside of the earth one, a good strategy is to first look for places where there’s liquid water and then you look in more detail like with further studies,” Saur says.

Scientist hope to one day send probes below the surface. They just have to find a way around the ice.

“There are even like ideas like how you actually would study the water and there is something like probes… that melt through the ice so that you get down into the liquid water like a submarine that wouldn’t just like explore the water,” he says.

Another one of Jupiter’s moons has a ocean whose water may be easier to study. NASA scientists have detected a plume of water vapor on the surface of Europa, the smallest of the four “Galilean satellites” or Jupiter’s largest moons. NASA is studying the possibility of sending a probe to Europa, the “Europa Clipper,” in the early 2020s.

Saur thinks that eventually, spacecraft might be able to sample Europa’s water vapor up close.

“The water is being spit out and then the spacecraft doesn’t need to drill through it but you can fly through it,” he says. “That would be a huge technical advantage.”

He for one, would be willing to go himself, should the opportunity ever present itself.

“I’m somebody who loves water all my life so I would go with you,” he says. “Just give me a ticket.”

This story was adapted from a broadcast on the PRI radio show Science Friday.