A new analysis of data collected by NASA’s Galileo spacecraft in 1997 has found strong evidence that the underground ocean of Jupiter’s moon Europa may be venting plumes of water vapor above the icy shell. The results appear in the journal Nature Astronomy.
The archival Galileo data were put through new computer models to untangle a mystery — a brief, localized bend in the magnetic field — that had gone unexplained until now. Previous images from the NASA/ESA Hubble Space Telescope in 2012 suggested the presence of plumes, but the new analysis used data collected much closer to the source and is considered strong, corroborating support for plumes.
“The data were there, but we needed sophisticated modeling to make sense of the observation,” said study lead author Dr. Xianzhe Jia, a space physicist at the University of Michigan.
At the time of the 1997 flyby, about 124 miles (200 km) above Europa’s surface, Galileo scientists didn’t suspect the spacecraft might be grazing a plume erupting from the icy moon.
Now, Dr. Jia and co-authors believe, its path was fortuitous. When the team examined the information gathered during that flyby, 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 ionized and leaves a characteristic blip in the magnetic field — they knew what to look for. And there it was on Europa — a brief, localized bend in the magnetic field that had never been explained.
The Galileo spacecraft carried a Plasma Wave Spectrometer (PWS) to measure plasma waves caused by charged particles in gases around Europa’s atmosphere. Dr. Jia and colleagues pulled that data as well, and it also appeared to back the theory of a plume.
But numbers alone couldn’t paint the whole picture. The researchers layered the magnetometry and plasma wave signatures into new 3D modeling, which simulated the interactions of plasma with solar system bodies. The final ingredient was the data from Hubble that suggested dimensions of potential plumes.
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 NASA’s Europa Clipper mission, which may launch as early as June 2022.
From its orbit of Jupiter, Europa Clipper will sail close by the moon in rapid, low-altitude flybys. If plumes are indeed spewing vapor from Europa’s ocean or subsurface lakes, the spacecraft could sample the frozen liquid and dust particles.
“There now seem to be too many lines of evidence to dismiss plumes at Europa,” said Europa Clipper project scientist Dr. Robert Pappalardo, from NASA’s Jet Propulsion Laboratory.
“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.”
Xianzhe Jia et al. Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures. Nature Astronomy, published online May 14, 2018; doi: 10.1038/s41550-018-0450-z