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Jupiter’s Moon Europa May Have Less Oxygen Than Previously Thought

The new findings could have implications for whether Europa’s vast ocean contains the conditions necessary to support life

Will Sullivan

Daily Correspondent

Artist's rendition of a spacecraft flying over Europa with Jupiter in the background
An artist's rendition of the Europa Clipper mission, set to launch to Europa in October. The mission could provide new insights about the life-supporting potential of the moon, which hosts a massive saltwater ocean beneath its icy surface. NASA / JPL-Caltech

Below the icy surface of Jupiter’s moon Europa lies a saltwater ocean. This body of water has long been considered a promising spot for hosting life, but a new study puts a bit of a damper on that idea.

In a paper published Monday in the journal Nature Astronomy, scientists suggest the Jovian moon is producing significantly less oxygen than past studies have calculated. The findings may mean that Europa has less potential for hosting life than previously thought, writes New Scientist’s Leah Crane.

More work will be needed to confirm the research, which contradicts previous telescope observations of oxygen in Europa’s ice, Kevin Hand, a NASA scientist who did not contribute to the findings, tells Marcia Dunn of the Associated Press (AP).

But even though the results suggest less oxygen exists on Europa, that level is “still compatible with microbial habitability for life as we know it,” Manasvi Lingam, an astrobiologist at the Florida Institute of Technology who was not involved in the study, says to Scientific American’s Sharmila Kuthunur.

Europa is considered one of the best candidates in the solar system for supporting extraterrestrial life. It’s covered by an icy shell, beneath which sits a watery ocean thought to be 40 to 100 miles deep. The moon’s diameter is only about a quarter of Earth’s, but its ocean is thought to hold more than twice as much water as our planet does.

When radiation from Jupiter reaches Europa’s crust of ice, it splits up the water molecules into their components, producing both hydrogen and oxygen. The moon has a thin atmosphere made mostly of oxygen, which comes from this reaction. Scientists think this oxygen, a building block for life, could find its way into the moon’s ocean and potentially support metabolism in life forms, according to a statement from NASA.

Before NASA’s Juno spacecraft, Europa’s atmosphere had never been directly observed, and estimates of oxygen from models varied widely, according to the new study. But in 2022, Juno flew within 220 miles of the moon’s surface, measuring the hydrogen and oxygen molecules produced by the radiation.

The study authors analyzed the data from Juno’s flyby and calculated that around 13 to 40 pounds of oxygen were being produced on Europa every second. This estimate was lower than those from previous studies, which had found that the Jovian moon was making as much as 2,000 pounds of oxygen per second.

While oxygen production was found to be in “a significantly narrower range than we previously thought, there’s still a lot we can learn,” Jamey Szalay, first author of the new study and a research scientist at Princeton University, says to the AP.

A lingering uncertainty is how much of this limited amount of oxygen makes it into the ocean, where life, if it exists, could make use of it. Some of the oxygen might stay in the ice or escape into the atmosphere.

“In some sense, the shell is like a lung for Europa. It’s continuously generating oxygen,” Szalay tells New Scientist. “That being said, we can’t speak to what happens after the oxygen is produced on the surface—it’s still a question how much of it could get into the ocean.”

Europa’s oxygen production could have been significantly higher in the past, the study authors note. Since Earth has greatly changed throughout its history, there’s “no reason to think that any other planetary body would have experienced an unchanging atmosphere for 4.5 billion years,” Emily Martin, a geologist at the National Air and Space Museum who did not contribute to the findings, tells Scientific American.

Juno isn’t the last chance scientists have to study Europa. Set to launch in October, NASA’s Europa Clipper mission will arrive at Jupiter in 2030 and will study whether Europa has conditions that could support life.

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Will Sullivan

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.