Behind its bright, snowy crust, Jupiter’s moon Europa is believed to harbor a salty ocean, making it a world that may be one of the most suitable places in our solar system.
However, life as we know requires oxygen. And it is still questionable whether Europa’s ocean has oxygen.
Now, astronomers have discovered how many molecules are created on this icy moon’s surface, which could be a source of oxygen for the water beneath. Using data from NASA’s Juno mission, the results, published Monday in the journal Nature Astronomy, show that these frozen worlds produce less oxygen than some astronomers might expect.
“The numbers are on the lower end of what we expected,” said Jamey Szalay, a plasma physicist at Princeton University who led the research. However, “it doesn’t completely preclude” the existence of life, he added.
On Earth, the photosynthesis of plants, plankton, and bacteria pumps oxygen into the atmosphere. However, this process is different on Europa. Charged particles from space crash into this moon’s icy crust, breaking the frozen water into hydrogen and oxygen molecules.
“This ice crust is like Europa’s lungs,” said Dr. Szalay. “The surface, which is the same as the surface that protects the ocean below from harmful radiation, is essentially ‘breathing’.”
Astronomers speculate that this oxygen may have migrated into Europa’s deep waters. If true, that oxygen could have mixed with volcanic material from the ocean floor, creating “a chemical soup that might have led to life,” said Fran Bagenal, a planetary scientist at the University of Colorado Boulder.
The Juno orbiter, launched in 2011 to find out what lies beneath Jupiter’s thick clouds, is now on an extended mission to explore the planet’s rings and moons. Inside the vehicle there is an instrument called JADE, which stands for Jovian Auroral Distributions Experiment. Dr. Team Szalay studied data collected by JADE as Juno flew through the plasma covering Europa.
However, the team wasn’t looking for oxygen directly; they’re calculating hydrogen. Because the molecules are so light, all the hydrogen produced on Europa’s surface floats high into the atmosphere. Oxygen, being heavier, is more likely to be at lower levels or trapped in ice.
“If we measure hydrogen, we can immediately know how much oxygen is produced,” said Dr. Szalay.
The team found that Europa’s surface produces about 13 to 40 pounds of oxygen every second. That equates to more than 1,000 tons per day, about enough to fill the Dallas Cowboys football stadium 100 times each year.
Although previous studies reported varying ranges, up to 2,245 pounds per second, these results suggest that the upper end of that range is likely not reached. However, according to Dr. Bagenal, this does not have to be detrimental to Europa’s habitability potential.
“We actually don’t know how much oxygen is needed to create life,” he said. So, the fact that the figure is lower than previous, more optimistic estimates is not a big deal.
Studying Europa’s atmosphere is “an important puzzle in understanding the moon as a system,” said Carl Schmidt, a planetary scientist at Boston University who was not involved in the research.
However, this finding only confirms the amount of oxygen born in the ice. The study doesn’t reveal how many molecules are lost to the atmosphere, or how the oxygen penetrates the ice to enrich the ocean beneath.
In other words, said Dr. Schmidt, “we still don’t know how much oxygen is going down rather than going up.”
Juno will not make another close flyby of this global water world, but the next generation of missions aimed specifically at studying Europa may find more answers. The European Space Agency’s Jupiter Icy Moons Explorer, expected 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 probe interactions between the moon’s icy crust and the water beneath it.
For now, astronomers have to work hard with data from Juno. Although the flyby lasted only a few minutes, it was the first time that the composition of plasma near Europa’s atmosphere was directly measured.
“This is just the tip of the iceberg,” said Dr. Szalay. “For many years, we will explore this only flyway to find all the treasures.”
2024-03-04 16:48:13
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