Scientists Reconsider Evidence of Water Vapor on Jupiter’s Moon

A new examination of 14 years of Hubble Space Telescope data has cast doubt on previous claims that Jupiter’s icy moon Europa periodically releases water vapor plumes. The research, published in Astronomy & Astrophysics, suggests earlier findings may have overestimated the certainty of these mysterious plumes, though the search for evidence continues.

Rethinking Europa’s Elusive Atmosphere

For over a decade and a half, scientists have studied Europa, fascinated by its icy crust and the potential subsurface ocean hidden beneath. Initial Hubble observations from 2012 suggested the moon might occasionally expel faint plumes of water vapor into space, raising hopes of studying Europa’s ocean without landing on its frozen surface. These plumes, if confirmed, could have significant implications for understanding the moon’s habitability.

“The evidence for water vapor plumes on Europa isn’t as strong as we first thought it was,” said SwRI’s Dr. Kurt Retherford, one of the authors of the 2014 paper that initially reported the phenomenon. Retherford and his colleagues recently published a new paper reanalyzing the data, providing a more cautious assessment of Europa’s tenuous atmosphere.

The new study focused on Lyman-alpha emissions, ultraviolet light scattered by hydrogen atoms, which can indicate escaping water molecules. By reassessing Hubble’s positioning and calibration, the team revealed uncertainties that could have affected earlier interpretations.

“One of the difficulties in interpreting the data back then was figuring out where to place Europa within its context,” Retherford explained. “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 by just a pixel or two, it could affect how the data gets interpreted.”

Confidence Levels Decrease, Questions Arise

The original research claimed a near-certain 99.9% confidence in the existence of water vapor plumes. The new analysis, detailed in Astronomy & Astrophysics, however, reduced that confidence to below 90%, which scientists say is insufficient to claim definitive evidence.

“Our reanalysis took our original 99.9% confidence in the plumes’ existence and reduced it to less than 90% confidence,” said Dr. Lorenz Roth of the Royal Technical Institute, Sweden, and lead author of the reanalysis. “That’s simply not enough evidence to support the certainty of claims we made at the time.”

The study does not rule out the possibility of plumes but highlights that prior data may have been misinterpreted. Retherford noted,

“The description of the phenomena just doesn’t hold up the same way anymore. The new data has 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.”

Comparisons With Other Icy Moons

Europa is not alone in showing potential geologic activity. Saturn’s moon Enceladus has confirmed water vapor plumes, and Jupiter’s Io ejects sulfur dioxide into space. These moons provide a framework for understanding Europa’s possible activity and demonstrate that plumes can occur in different chemical and physical environments.

Scientists are particularly interested in Europa because of its vast saltwater ocean beneath the icy shell. Cracks in the ice could serve as pathways for water to escape, but confirmation will require direct observation. NASA’s upcoming Europa Clipper mission, scheduled to arrive in 2030, is expected to provide definitive measurements that will settle lingering questions about Europa’s atmosphere and plume activity.