Scientists may have discovered water on Europa, the smallest of the four Galilean moons orbiting Jupiter, after re-examining data collected by NASA's Galileo spacecraft, which was launched in 1989 and arrived around Jupiter in 1995.
NASA said the findings provide evidence that Europa has a subsurface liquid water reservoir that is venting plumes of water vapour above its icy shell.
If true, it could bring new insights to the question of whether it could support life in any form, notwithstanding its cold surface temperature.
The new and advanced computer examinations unearth what NASA call a mystery in the data: a "brief, localised bend in the magnetic field".
While previous ultraviolet images from NASA's Hubble Space Telescope in 2012 suggested the presence of plumes, the anomaly had gone unexplained until now.
However, the new analysis used data collected much closer to the source and is considered strong, corroborating support for plumes.
The research was led by University of Michigan physicist Xianzhe Jia. His team was inspired to dive back into the Galileo data after a member of the Europa Clipper science team, Melissa McGrath, delivered a presentation highlighting other Hubble observations of Europa.
"The data was there, but we needed sophisticated modelling to make sense of the observation," Jia said.
"One of the locations she mentioned rang a bell. Galileo actually did a flyby of that location, and it was the closest one we ever had. We realised we had to go back.
"We needed to see whether there was anything in the data that could tell us whether or not there was a plume."
When they examined the information gathered during the flyby some 21 years ago, magnetometer data showed a bend in the magnetic field. Until now that had not been explained.
However, they knew this had to be evidence of a plume because previous missions have proven that material in plumes becomes ionised, leaving a "characteristic blip" in the magnetic field.
The team also visited a measurement Galileo carried out during its quest: a powerful Plasma Wave Spectrometer, which measures plasma waves caused by charged particles in gases around Europa's atmosphere. This also appeared to back the theory of a plume, the scientists said.
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