Water vapor plumes on Jupiter's Europa A new SwRI study has raised doubts about the existence of water vapor plumes on Jupiter’s moon Europa (shown above), initially reported based on Hubble Space Telescope observations from 2012. A reanalysis of the data reduced the certainty of that initial finding, but scientists are still hopeful that such plumes will be observed at some point in the future.
Image Credit: Courtesy of NASA
Scientific Frontline: Extended "At a Glance" Summary: Reconsidering Europa's Vapor Plumes
The Core Concept: A comprehensive reanalysis of 14 years of Hubble Space Telescope data has cast doubt on previous assertions that Jupiter's moon Europa actively discharges faint water vapor plumes. The new findings suggest that earlier detections may have been the result of statistical noise and instrument alignment uncertainties rather than actual geyser activity.
Key Distinction/Mechanism: Initial studies pushed the limits of the Hubble telescope to detect trace amounts of water vapor. However, the reanalysis demonstrated that placing Europa's exact position within the image context was highly sensitive; a misalignment of just a pixel or two fundamentally altered data interpretation, reducing the statistical confidence of the plumes' existence from 99.9% to less than 90%.
Major Frameworks/Components:
- Space Telescope Imaging Spectrograph (HST/STIS): The specific instrument aboard the Hubble Space Telescope utilized to capture the long-term observational data of the icy moon.
- Lyman-Alpha Emissions: A specific wavelength of ultraviolet light emitted and scattered by hydrogen atoms, which scientists use as a primary chemical marker to hunt for atmospheric water vapor.
- Statistical Reanalysis: The methodological correction applied to account for spatial uncertainty, image placement errors, and signal-to-noise ratios in deep-space telescopic observations.
Branch of Science: Planetary Science, Astrophysics, and Astronomy.
Future Application: These corrected models are vital for the planning of upcoming deep-space missions, such as NASA's Europa Clipper. By acknowledging the lack of concrete evidence for continuous plumes, engineers and scientists must prioritize alternative orbital sampling technologies and ice-penetrating radar to assess the moon's subsurface ocean.
Why It Matters: Europa is considered one of the most promising candidates for hosting extraterrestrial life due to its vast subsurface liquid water ocean. Determining whether this ocean vents its contents into space is critical, as it directly impacts how future probes might attempt to sample its chemistry and search for biosignatures.
Analyzing 14 years of Hubble Space Telescope data regarding Jupiter’s moon Europa has provided Southwest Research Institute (SwRI) scientists with a better understanding of its tenuous atmosphere. The findings cast doubt on previous evidence suggesting that the icy moon intermittently discharges faint water vapor plumes from a presumed subsurface ocean.
“The evidence for water vapor plumes on Europa isn’t as strong as we first understood it,” said SwRI’s Dr. Kurt Retherford, coauthor of the 2014 paper that initially made the assertion. Retherford and his colleagues recently published a new paper reanalyzing the data.
The new paper examines the past 14 years of data from the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (HST/STIS), focusing on Europa’s Lyman-alpha emissions. Lyman-alpha is a specific wavelength of ultraviolet light emitted and scattered by hydrogen atoms. From 2012 to 2014, the team pushed the limits of the 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.”
Consequently, what was previously thought to be evidence of a water vapor plume could simply 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 of the Royal Institute of Technology in Sweden, the paper’s lead author. “That’s simply not enough evidence to support the certainty of claims we made at the time.”
Retherford noted that 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 for them.
“The description of the phenomena just doesn’t hold up the same way anymore,” said Retherford. “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.”
SwRI scientists still hope to find water vapor plumes escaping from Europa. Similar water vapor plumes have been confirmed on Saturn’s moon Enceladus; additionally, Europa’s neighbor Io, another of Jupiter’s moons, exhibits plumes of sulfur dioxide expanding into space.
Scientists are particularly interested in Europa because its icy surface is thought to obscure a vast, subsurface saltwater ocean. Cracks in Europa’s icy shell could provide pathways for liquid water to rise to the surface and erupt into space. This phenomenon remains a distinct possibility that NASA’s Europa Clipper mission will investigate when it arrives in the Jovian system in 2030.
Published in journal: Astronomy & Astrophysics
Title: Europa’s Lyman-α emissions from HST/STIS observations
Authors: L. Roth, K. D. Retherford, J. Saur, D. F. Strobel, T. Becker, S. Bergman, A. Blöcker, S. R. Carberry Mogan, C. Grava, M. Ivchenko, S. Joshi, M. A. McGrath, F. Nimmo, L. Paganini, W. Pryor, and J. R. Spencer
Source/Credit: Southwest Research Institute
Reference Number: ps051826_01