Scientists presented further evidence Monday for water plumes on the surface of Jupiter's moon Europa, raising hopes of probing the jets for signs of life around the second planet from Earth.
Europa's frozen surface has long been thought to cover a salty ocean about twice the size of our planet's.
Given the suspected abundance of warm, liquid water under its kilometres-thick ice shell, the moon is considered a "top candidate" by NASA for life on a Solar System body other than Earth.
But sending a robot craft to land on Europa and drill through its surface would be a much more costly and complicated endeavour than, say, flying through a plume of water ejected from the moon's innards, and measuring its composition.
Twice before has NASA reported evidence, from its Hubble Space Telescope, for the existence of water plumes on Europa, though this interpretation has caused much debate.
The new data, reported in the scientific journal Nature Astronomy, comes from measurements made from much closer up during a flyby of NASA's now-expired Galileo spacecraft.
The data was captured on Galileo's closest encounter with the moon on December 16, 1997, and has now been re-examined for evidence that a blip in the data it captured was caused when it crossed a water plume.
The spacecraft, launched in 1989 to examine the fifth planet from the Sun with its dozens of moons, became the first in 1995 to enter the orbit of a gas giant planet.
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.
For the new study, experts measured variations in the moon's magnetic field and plasma waves as measured during Galileo's close flyby, and found they were "consistent" with the spacecraft crossing a plume.
"These results provide strong independent evidence of the presence of plumes at Europa," they wrote.
The team reconstructed the spacecraft's path to pinpoint the plume's location on the moon's surface.
"These findings will help plan future missions to Europa, such as NASA’s Europa Clipper and ESA’s Jupiter Icy Moons Explorer spacecraft, both of which are expected to arrive at Jupiter between the late 2020s and early 2030s," said a Nature summary.