New research led by planetary scientists from Southwest Research Institute and KTH Royal Institute of Technology suggests that evidence for vapor erupting from Jupiter’s icy moon Europa may be less conclusive than once believed.
This is an artist’s impression of a water-vapor geyser on Europa. Image credit: University of Cologne.
“The evidence for water vapor plumes on Europa isn’t as strong as we first understood it,” said Dr. Kurt Retherford, a researcher at Southwest Research Institute one of the authors of a 2014 paper initially making that assertion.
In the new study, Dr. Retherford and his colleague analyzed data collected by the Space Telescope Imaging Spectrograph (HST/STIS) aboard the NASA/ESA Hubble Space Telescope in 1999 and between 2012 and 2020.
They focused on Europa’s Lyman-alpha emission, a specific wavelength of ultraviolet light emitted and scattered by hydrogen atoms.
“One of the difficulties in interpreting the data back then was determining where to place Europa within its context,” Dr. Retherford said.
“The way Hubble works left some uncertainty in terms of placement relative to the center of the image.”
“If Europa’s placement was off even just by a pixel or two, it could affect how the data gets interpreted.”
As a result, what the researchers thought could be evidence of a water vapor plume could also just be statistical noise.
“Our reanalysis took our original 99.9% confidence in the plumes’ existence and reduced it to less than 90% confidence,” said Dr. Lorenz Roth, a researcher at KTH Royal Institute of Technology.
“That’s simply not enough evidence to support the certainty of claims we made at the time.”
“The current dataset does not rule out the possibility of the water vapor plumes described in the 2014 paper, but it no longer provides concrete evidence of them,” Dr. Retherford said.
“The description of the phenomena just doesn’t hold up the same way anymore.”
“The new data have made us reconsider the strength of the previous paper’s conclusion regarding water vapor plumes.”
“The recent analysis also provides improved information about the neutral hydrogen atom component of Europa’s escaping atmosphere, originating from its water ice surface.”
“We still hope to find water vapor plumes escaping from Europa.”
“Similar water vapor plumes have been confirmed on Saturn’s moon Enceladus, and Europa’s neighbor Io, another moon of Jupiter, has plumes of sulfur dioxide expanding out into space.”
The team’s new paper was published May 5 in the journal Astronomy & Astrophysics.
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L. Roth et al. 2026. Europa’s Lyman-α emissions from HST/STIS observations. A&A 709, A59; doi: 10.1051/0004-6361/202659406
