NASA spacecraft provides new evidence of water plumes on Europa

Scientists re-examining data from an old NASA spacecraft have found evidence that the liquid water reservoir under the surface of Jupiter's moon Europa are venting plumes above its icy shell.

Data collected by NASA's Galileo spacecraft in 1997 was put through new and advanced computer model to untangle a mystery - a brief, localised bend in the magnetic field - that had gone unexplained until now.

Previous ultraviolet images from NASA's Hubble Space Telescope in 2012 suggested the presence of plumes.

However, the new analysis published in the journal Nature Astronomy, used data collected much closer to the source and is considered strong, corroborating support for plumes.

"There now seem to be too many lines of evidence to dismiss plumes at Europa," said Robert Pappalardo, Europa Clipper project scientist at NASA's Jet Propulsion Laboratory (JPL) in the US.

"This result makes the plumes seem to be much more real and, for me, is a tipping point. These are no longer uncertain blips on a faraway image," said Pappalardo.

At the time of the 1997 flyby, about 200 kilometers above Europa's surface, the Galileo team did not suspect the spacecraft might be grazing a plume erupting from the icy moon.

When they examined the information gathered during that flyby 21 years ago, sure enough, high-resolution magnetometer data showed something strange.

Drawing on what scientists learned from exploring plumes on Saturn's moon Enceladus - that material in plumes becomes ionised and leaves a characteristic blip in the magnetic field - they knew what to look for.

Scientists detected a brief, localised bend in the magnetic field that had never been explained.

They layered the magnetometry and plasma wave signatures into new 3D modelling developed at the University of Michigan in the US, which simulated the interactions of plasma with solar system bodies.

The final ingredient was the data from Hubble that suggested dimensions of potential plumes, NASA said.

The result that emerged, with a simulated plume, was a match to the magnetic field and plasma signatures the team pulled from the Galileo data.

The findings are good news for the Europa Clipper mission, which may launch as early as June 2022, NASA said.

From its orbit of Jupiter, Europa Clipper will sail close by the moon in rapid, low-altitude flybys, it said.

If plumes are indeed spewing vapour from Europa's ocean or subsurface lakes, Europa Clipper could sample the frozen liquid and dust particles.