Experiments Explain Mysterious Distribution of Hydrogen Peroxide on Europa
by Southwest Research Institute
Southwest Research Institute (SwRI) scientists conducted laboratory experiments to address a mystery regarding the origins of frozen hydrogen peroxide (H2O2) on Jupiter's icy moon Europa. Their results, published in the July 2025 issue of Planetary Science Journal, may help explain puzzling observations made by the James Webb Space Telescope (JWST).
Scientists studying the telescope data observed elevated levels of hydrogen peroxide on Europa in unexpected areas. Decades of laboratory studies suggested that higher concentrations of hydrogen peroxide would reside in the colder, polar regions, but JWST revealed the opposite—the highest peroxide concentrations were at the warmer equatorial chaos terrain known as Tara Regio.
This puzzle inspired Bereket Mamo, a graduate student at The University of Texas at San Antonio and a SwRI contractor, to submit a NASA proposal for a series of experiments to investigate the mystery. He received a Future Investigators in NASA Earth and Space Science and Technology grant to help fund the research at SwRI's Center for Laboratory Astrophysics and Space Science Experiments (CLASSE) facility.
Mamo and colleagues noted that the chaos terrains with enhanced hydrogen peroxide also showed elevated levels of carbon dioxide (CO2). Scientists theorize that CO2 may be seeping up through cracks in the ice crust from a presumed subsurface liquid ocean.
"We simulated the surface environment of Europa inside a vacuum chamber by depositing water ice mixed with CO2," Mamo said. "We then irradiated this ice mixture with energetic electrons to observe how the peroxide production changed."
The SwRI experiments demonstrated that trace amounts of CO2 in water ice can significantly enhance hydrogen peroxide production at temperatures found on the surface of Europa, helping explain the new JWST observations.
Dr. Ujjwal Raut, program manager in SwRI's Planetary Science Section and Mamo's advisor, indicated that a key factor driving their research is assessing the potential habitability of Europa. The occurrence of increased hydrogen peroxide in a region that has evidence of CO2, sodium chloride, and other species of interest is intriguing.
According to Raut, this finding hints at a chemical cycle where materials rising to Europa's icy surface from a subsurface ocean are irradiated, creating chemical potential in the form of oxidants like hydrogen peroxide. Such oxidants can be cycled back to the ocean over geological timescales where they may react with reductants coming from Europa's seafloor to release chemical energy possibly capable of supporting life.
"Synthesis of oxidants such as hydrogen peroxide on Europa's surface is important from an astrobiological perspective," noted Richard Cartwright from Johns Hopkins University Applied Physics Laboratory and a co-author of the paper. "In fact, an entire NASA mission, the Europa Clipper, is en route to the Jovian system right now to explore the icy moon and help us understand its habitability."
"Our experiments provide clues to better understand JWST Europa observations and serve as a prelude to upcoming close-range investigations by Europa Clipper and ESA's JUICE spacecraft," Cartwright added.
"When you have a source of carbon from the interior, such as from an interior ocean like on Europa, and you combine it with energy from the magnetosphere, it produces new species on the surface, including hydrogen peroxide and other organic compounds, that store chemical energy," stated Dr. Ben Teolis, a planetary scientist at SwRI and another co-author of the paper.
"Chemical energy is important as it is a necessary ingredient for dark habitable ocean worlds where sunlight doesn't reach."
These findings provide a plausible explanation for the perplexing hydrogen peroxide distribution on Europa. They also have implications for understanding its presence on other icy bodies, such as Jupiter's moon Ganymede and Pluto's moon Charon, where hydrogen peroxide has been detected along with CO2.
More information: Bereket D. Mamo et al, Laboratory Investigation of CO2-driven Enhancement of Radiolytic H2O2 on Europa and Other Icy Moons, The Planetary Science Journal (2025). DOI: 10.3847/PSJ/ade3d8
Journal information: The Planetary Science Journal
