Europa's Famous Water Plumes May Have Been a Trick of the Light

In 2013, astronomers detected faint ultraviolet emissions from Europa's southern hemisphere using the Hubble Space Telescope and interpreted the signal as water vapor escaping from the moon's surface — evidence that liquid water was finding its way out of Europa's subsurface ocean. Now the same researchers have gone back through a decade of data and concluded, with admirable candor, that they were probably wrong.

The new study examines 14 years of Hubble observations using its Imaging Spectrograph, focusing on Europa's Lyman-alpha emissions: a specific ultraviolet wavelength emitted and scattered by hydrogen atoms. The team found two problems with the original analysis. First, Europa occupies only a small fraction of Hubble's 1,000 x 1,000-pixel detector; an alignment error of even one or two pixels skews how the data gets interpreted. Second, hydrogen atoms scattering sunlight produce a natural glow around the satellite. That halo caused researchers to overestimate the photon count at the moon's limb. Once the team corrected target alignment and accounted for the background glow, the plume signature dissolved.

The reanalysis dropped their original 99.9 percent confidence in the plumes to under 90 percent. "That's simply not enough evidence to support the certainty of claims we made at the time," said lead author Lorenz Roth.

Two pixels. A decade of excited papers. It is, as miscalibrations go, rather a lot to rest a subsurface ocean narrative on.

Europa's geologically active surface and magnetic readings still offer strong independent evidence for that ocean. The ocean almost certainly remains. The convenient exit door, however, may never have been there.

Read the full story at Sky & Telescope, June 3, 2026

Hot Take: There is a particular kind of scientific integrity involved in being the researcher who discovered a thing and then publishing the paper that undoes your own discovery, and it deserves more credit than it typically gets.