Hubble Data Reanalysis Lowers Confidence in Europa's Water Plumes

Confidence in the existence of water vapor plumes on Europa, one of Jupiter's moons, has significantly decreased following a reanalysis of Hubble telescope data. What was reported as promising evidence in 2014 is now considered less conclusive, according to new findings from a team of researchers.

Astronomers in 2014 had reported evidence of faint plumes detected through Lyman-alpha emissions, a specific ultraviolet wavelength associated with hydrogen atoms. This data hinted that water vapor escaping from Europa's surface could be breaking apart into hydrogen and oxygen in space, a key indicator of geological activity.

Europa has long fascinated scientists because beneath its geologically active yet frozen "chaos terrain" of ridges and valleys lies what is believed to be a vast saltwater ocean. If water vapor plumes exist, they could provide a rare opportunity to study material from the moon’s hidden ocean without drilling through miles of ice, though that would still require a spacecraft flyby.

"The evidence for water vapor plumes on Europa isn’t as strong as we first understood it."

However, researchers now state that the original data analysis pushed the Hubble telescope to the limits of its capabilities. Dr. Kurt Retherford of Southwest Research Institute, a co-author of both the original 2014 study and the new reanalysis paper, confirmed that "the evidence for water vapor plumes on Europa isn’t as strong as we first understood it."

What was thought to be evidence of a water vapor plume could simply be statistical noise. Dr. Lorenz Roth of the KTH Royal Institute of Technology, Sweden, the paper’s lead author, explained that "our reanalysis took our original 99.9% confidence in the plumes’ existence and reduced it to less than 90% confidence." For Roth, "that’s simply not enough evidence to support the certainty of claims we made at the time."

Despite these revised findings, scientists remain optimistic that Europa could still harbor active plumes. For instance, Saturn's moon Enceladus has directly confirmed water vapor jets. Jupiter’s moon Io also produces dramatic volcanic plumes, although these are composed of sulfur dioxide.

Even if its water vapor plumes are less certain, Europa’s fractured icy crust could still provide pathways for water from the subsurface ocean to escape into space. Scientists hope future missions will settle the question once and for all.

Among these missions is NASA’s Europa Clipper, scheduled to arrive in the Jupiter system in 2030. This spacecraft will closely study Europa’s icy shell, atmosphere, and possible subsurface ocean. Meanwhile, the European Space Agency’s JUpiter ICy moons Explorer (JUICE) will arrive in 2029 and take three and a half years to examine Europa, as well as two of Jupiter’s other Galilean moons, Ganymede and Callisto.

These upcoming explorations promise to deliver crucial data that could definitively confirm or rule out the presence of plumes, offering an unprecedented look into Europa's habitability potential.