Europa, Jupiter’s possibly habitable moon, may not have as much oxygen – 03/07/2024 – Science

Beneath its shiny, icy shell, Jupiter’s moon Europa may harbor a salty ocean, making it a world that could be one of the most habitable places in our solar system.

But life, as we know it, needs oxygen. And it’s an open question whether Europa’s ocean has it.

Now, astronomers have determined how much of the molecule is produced on the icy moon’s surface, which could be a source of oxygen for the waters below. Using data from NASA’s Juno mission, the results, published Monday in the journal Nature Astronomy, suggest that the frozen world generates less oxygen than some astronomers might have expected.

“It’s at the lower end of what we would expect,” said Jamey Szalay, a plasma physicist at Princeton University who led the study. But it’s “not completely prohibitive” for livability, he added.

On Earth, photosynthesis by plants, plankton and bacteria pumps oxygen into the atmosphere. But the process works differently in Europe. Charged particles from space bombard the moon’s icy crust, breaking down the frozen water into hydrogen and oxygen molecules.

“The ice shell is like Europa’s lungs,” Szalay said. “The surface — which is the same surface that protects the ocean beneath from harmful radiation — is, in a sense, breathing.”

Astronomers speculate that this oxygen may move into Europa’s watery underworld. If so, it could mix with volcanic material on the seafloor, creating “a chemical soup that could end up generating life,” said Fran Bagenal, a planetary scientist at the University of Colorado Boulder.

The Juno probe, which was launched in 2011 to discover what lies beneath Jupiter’s thick veil of clouds, is now on an extended mission exploring the planet’s rings and moons. On board the vehicle is an instrument called Jade, short for Jovian Auroral Distributions Experiment. Szalay’s team studied data collected by Jade as Juno flew through the plasma surrounding Europa.

But they weren’t directly looking for oxygen — they were counting hydrogen. Because the molecule is so light, all the hydrogen produced on Europa’s surface floats high in the atmosphere. Oxygen, which is heavier, is more likely to stay lower or remain trapped in the ice.

But both molecules come from the same source: decomposed frozen water.

“And so if we measure hydrogen, we have a direct line to determine how much oxygen is produced,” Szalay said.

The team found that about 13 to 40 pounds of oxygen are generated every second by Europa’s surface. That’s more than 1,000 tons per day, roughly enough to fill the Dallas Cowboys’ football stadium 100 times a year.

While previous studies reported widely varying ranges of up to 2,245 pounds per second, this result shows that the upper limit of that range was unlikely. But, according to Bagenal, this does not necessarily harm Europa’s habitability potential.

“We don’t really know how much oxygen is needed to generate life,” she said. “So the fact that it’s lower than some previous estimates isn’t a big deal.”

Studying Europa’s atmosphere is “an important piece of the puzzle for learning about the moon as a system,” said Carl Schmidt, a planetary scientist at Boston University who was not involved in the work.

But the findings only confirm the amount of oxygen born in the ice. The study doesn’t reveal how much of the molecule is lost to the atmosphere, or how it might permeate the ice to enrich the ocean below.

In other words, Schmidt said, “We still have no idea how much is going down compared to how much is going up.”

Juno will no longer make close flybys of the global water world, but next-generation missions specifically designed to study Europa may find more answers. The European Space Agency’s Jupiter Icy Moons Explorer, scheduled to arrive in the Jovian system in 2031, aims to confirm the existence and size of Europa’s ocean. And NASA’s Europa Clipper, scheduled to launch in October, will investigate how the moon’s icy shell interacts with the water below.

For now, astronomers have a lot of work to do with Juno’s data. Although the pass lasted just a few minutes, it was the first time that the composition of plasma near Europa’s atmosphere had been directly measured.

“This is just the tip of the iceberg,” Szalay said. “For many years, we will be digging just this single flyby to find the treasure.”