- NASA's Juno mission found that Jupiter's icy moon Europa produces 1,000 tons of oxygen every 24 hours.
- It's enough to keep a million people breathing for a day but is much less than previously thought.
About 400 million miles away, floating in deep space, is a water world called Europa that produces 1,000 tons of oxygen every 24 hours. That's enough oxygen to keep a million people alive for a day, NASA reported this week.
However, these new estimates, published in the peer-reviewed journal Nature Astronomy, aren't meant to determine how many people could inhabit this moon of Jupiter. They're helping scientists figure out whether, or not, Europa hosts life of its own.
"We think that Europa is the most likely place to look beyond Earth for life today," said Curt Niebur, NASA's lead scientist for outer planet exploration who wasn't involved with the study.
If life forms exist on Europa, they might look like microbes, or perhaps something more complex, according to NASA. But they wouldn't be visible from the surface, which is a frozen desert.
They'd most likely exist in the moon's vast underground ocean that may contain as much as twice the amount of water as Earth.
While water is one key ingredient for life, as we know it, it's not the only one. There's a laundry list of other chemicals that scientists are looking for — oxygen being one of them.
Now, NASA's Juno spacecraft, which is currently flying around Jupiter and its moons, has taken the most precise estimate of Europa's oxygen production to date. And it turns out to be a lot less than we thought.
The latest estimate of 1,000 tons of oxygen every 24 hours is more than 86 times less than some previous estimates. And this new data may call Europa's habitability into question.
How Europa produces oxygen
Oxygen production looks very different on Europa than on Earth. Whereas Earth gets its oxygen from photosynthesis, Europa's is a result of its parent planet Jupiter.
Jupiter emits powerful radiation that showers Europa with high-energy particles. These particles then interact with frozen water ice (H2O) on the moon's surface.
The interaction splits the H2O molecules apart into hydrogen and oxygen gas. But where that oxygen goes is the big question. Some of it may get stuck in the ice, some may escape to space, and some may travel downward into Europa's subsurface ocean.
If enough oxygen reaches underground, that would mean Europa's ocean has one of the critical ingredients for life as we know it. "But that's a big question mark for us," since the oxygen can end up in so many different places, Niebur said.
What NASA's Juno mission has done is shed more light on the total amount of oxygen that Europa's surface generates. It's still not clear, however, how much, if any, seeps into the underground ocean.
Measuring oxygen on Europa
To measure how much oxygen Europa's surface generates, scientists used the Jovian Auroral Distributions Experiment (JADE) instrument on board Juno.
JADE was designed to measure charged particles in Jupiter's auroral regions. But when Juno flew by Europa in September 2022, JADE successfully measured the charged particles shed from the moon's atmosphere for the very first time.
Using the JADE data, scientists estimated the total amount of hydrogen (not oxygen) gas in Europa's thin atmosphere. Since there is one oxygen atom for every two hydrogen atoms in a water molecule, scientists could use the hydrogen gas data to then calculate the amount of oxygen generated on the surface.
"This has really refined and narrowed down our understanding of how much oxygen is made in the surface," said study lead author Jamey Szalay, a space physics researcher at Princeton University.
"But we don't know how much of it leaves the surface and how much of it makes its way to the ocean," Szalay added. NASA's next Europa mission, Clipper, could bring us closer to answering that question.
An ongoing search for the possibility of life
NASA's Europa Clipper mission is scheduled to launch in October 2024. Its primary objective is to determine whether or not Europa is habitable.
Clipper will be equipped with instruments that should help reveal Europa's inner structure, such as its subsurface radar. With this tool, NASA scientists will peer down tens of miles below the crust to identify features that could help determine whether oxygen is reaching the subsurface ocean, Niebur told BI.
"Clipper is an incredibly exciting mission, and it has important science objectives that will likely revolutionize our understanding of the ice shell, the subsurface ocean, and how they interact with each other," Szalay said.
While finding out whether Europa's subsurface ocean contains oxygen, or not, would improve our understanding of the moon's habitability, it won't automatically confirm whether life exists, or could exist, on Europa.
"The amount of oxygen available on Europa is not a binary switch you flip to decide whether or not life could be present," Niebur explained.
He pointed out that life existed on Earth for about 1.5 billion years without oxygen. If it could happen here, it could happen on this faraway moon, too.
As for the Juno mission, Szalay will continue working through the data they retrieved during this Europa flyby.
"For years to come, we're going to be digging through this and learning everything we can," he said.