Europa in true color, taken by Juno September 2022.
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The uncertainty of science: Based on a re-analysis of data from the Hubble Space Telescope, scientists now say that the plumes of water vapor that Hubble had supposedly detected erupting from the surface of the Jupiter moon Europa might not exist, and could instead simply be statistical noise in the data.

The new paper looks at the last 14 years of data from the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (HST/STIS) focused on Europa’s Lyman-alpha emissions. Lyman-alpha is a specific wavelength of ultraviolet light emitted and scattered by hydrogen atoms. From 2012-2014, the team was pushing the limits of the Hubble telescope’s capabilities.

“One of the difficulties in interpreting the data back then was determining where to place Europa within its context,” 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 they 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 (KTH Royal Institute of Technology, Sweden), the paper’s lead author. “That’s simply not enough evidence to support the certainty of claims we made at the time.”

The plumes might still exist, but the data used here is simply more uncertain that previously thought. It is hoped that when Europa Clipper and Juice both enter Jupiter orbit in a few years they will be able to settle this issue more definitively.