Galileo was passing some 124 miles (200 kilometres) above Europa's surface when it apparently flew through the plume.
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.
The newest proof was discovered among data collected by the Galileo mission in 1997 during a Europa flyby. The study, published Monday in the journal Nature Astronomy, adds to the mounting evidence that Europa is spewing its contents into space.
Europa is among the most enticing destinations of the Solar System to pursue the presence of life beyond the Earth.
The implications could be enormous.
At a meeting in Maryland, near Washington, scientists preparing the next mission to Europa, the Europa Clipper, set for 2022, had the idea to check the old Galileo data to see if they could find confirmation of what Hubble noticed in 2012, namely jets of water vapour coming from inside the icy moon of Jupiter.
This could help scientists to determine if Europa's ocean is habitable to life - or detect signs of it directly - without having to land a probe on the moon's surface.
"I think it tells you there's probably more plumes than we can see right now, because the odds that we'd happen to fly through the only one that exists are pretty low", McGrath says. 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. That's another requirement for life that might be checked off the list - in fact, some scientists theorize that life on Earth started in the deep sea vents that erupt in geysers.
Before ending its mission in 2003 with a planned crash into Jupiter's atmosphere, Galileo reported the first data suggestive of a liquid water ocean under Europa's surface.
NASA's Hubble Space Telescope has spotted tantalizing signs of such a plume multiple times over the past half decade, but those measurements were near the limits of the powerful instrument's sensitivity. During this trip, the spacecraft swung by Europa 11 times, conducting radio experiments that hint of an atmosphere. So a team of United States astronomers went back and took a second look at data collected by the Galileo spacecraft during its eight-year stay in the Jovian system.
Last month researchers found two lakes hidden under thick ice in Canada that could be similar to the conditions found on Jupiter's moon Europa. Galileo actually did a flyby of that location, and it was the closest one we ever had.
"There were some odd signatures in the magnetic field that we had never really been able to account for", Kivelson, who now works at the University of California, Los Angeles, said Monday on NASA TV. Second, these plumes mean that a spacecraft could have easy access to Europa's water without having to drill through its ice crust. Old data has turned up new evidence of water plumes spraying through the icy shell into space.
Their discovery not only suggests Europa's watery plumes really do exist, but are also frequent and widespread.
"This one certainly stood out as very special", the study's lead author Xianzhe Jia said. "We can even collect dust particles".
A mission called Europa Clipper was proposed several years ago.
Scientists believe Jupiter's moon Europa has a greater life-supporting potential than previously thought, and NASA is planning to send a spacecraft to investigate.
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 odd.