Several images from the Hubble Space Telescope have also suggested that the moon might be venting out plumes, but the latest analysis of the data, which was collected up close on the icy moon, is probably the strongest evidence backing up the theory of subsurface water.
But the probe never directly encountered any of that water - or so scientists thought at the time.
The implications could be enormous.
Scanning the Canadian lakes for signs of basic microbial life could help scientists in the upcoming Clipper mission which will look for alien life on Europa. Nutrients sprayed onto the ice by the nearby volcanic moon Io, the thinking goes, may sink down to the ocean floor and serve as food. Now, a new report is helping to cement the idea that jets of water spewing from cracks in the planet's icy shell are a good place to start looking for evidence of life. Philips noted that collected plume material might not even be a direct sample of ocean water, but it would still "yield important insights into the composition of materials within Europa, and the potential for habitability-could there be environments on Europa where life could survive?" But until now, solid evidence has been hard to come by.
Images captured by the Hubble Telescope have previously suggested the presence of ocean plumes ejected through tissues in the icy crust of Jupiter's moon.
Artist's illustration of Jupiter and Europa (in the foreground) with the Galileo spacecraft after its pass through a plume erupting from Europa's surface.
To their delight, the scientists found such a signal on December 16, 1997, during the spacecraft's E12 orbit.
Flying at 6km (3.7 miles) a second Galileo made its closest ever flyby, shooting across the surface at an altitude of 200km (125 miles) when it detected something unusual. The magnetic field lines (depicted in blue) show how the plume interacts with the ambient flow of Jovian plasma. Mike Brown, a planetary scientist at the California Institute of Technology, said in a tweet he is a "big Europa fan", but "so far, all of the evidence for plumes on Europa has been hopeful, rather than truly convincing". Xianzhe Jia, a University of MI space scientist, and his colleagues published their findings on May 14 in Nature Astronomy.
"The data were there, but we needed sophisticated modeling to make sense of the observation", Jia said.
When plumes of water spray out of Europa, the molecules are immediately battered by highly energetic particles, a process that smashes them into charged ions.
To verify this monumental discovery, the space agency is planning a new expedition to Jupiter's moon. But that still means an orbiting spacecraft, like the Europa Clipper mission that's tentatively scheduled to launch in the early 2020s, could sample a plume and get a glimpse of what lies beneath the moon's ruddy, crisscrossed rind.
The Europa Clipper mission is expected to shed more light on the elusive moon with rapid, low-altitude flybys from its orbit. What they found is that magnetometer readings and radio signals also showed anomalies when the craft flew over the area of the purported plumes determined by Hubble.
Because the plumes erupt like geysers "there may be ways for that material from the ocean to come out above that ice shell and that means we would be able to sample it", she added. Would it use the same chemistry to store and use energy?