Europa is objectively one of the most badass moons in the solar system.
The relatively small moon of Jupiter is thought to have a liquid water ocean beneath its icy shell, and it's considered one of the most likely places to host alien life in our solar system.
Now, thanks to a new study published in the journal Nature Astronomy this week, we may be inching closer to figuring out if Europa could host life in the ocean hidden beneath its frozen surface.
According to the new study, NASA's Galileo spacecraft — which ended its mission by purposefully crashing into Jupiter's atmosphere in 2003 — likely flew through a plume of water erupting from Europa in 1997.
We just didn't know about it until now.
"This is potentially great news for future exploration of Europa, because spacecraft may have a chance to directly sample materials that are linked to the subsurface ocean," Xianzhe Jia, lead author of the study, said via email.
"Observations of plumes may tell us a lot about whether or not Europa’s ocean has the ingredients suitable for life."
Circumstantial evidence, but a lot of it
The team of researchers behind the new study re-analyzed the data gathered by Galileo 20 years ago and found evidence that the spacecraft did, in fact, fly through a plume of water shot into space from Europa.
Jia explained that the team was inspired to take another look at the Galileo data because the Hubble Space Telescope recently found some evidence for possible plumes shooting from Europa. That Hubble data, however, wasn't definitive proof of erupting plumes because it's such a difficult observation to make from Earth's orbit.
"When we took a detailed look at the Galileo data obtained more than 20 years ago, we saw those peculiar signals in both the magnetic field and plasma wave data that no one seemed to have explained before," Jia said.
"The data has been there for a long time, but it didn’t get picked up by us until recently after we saw those Hubble images that seem to suggest Europa might have plumes erupting into space."
The team used numerical models to try to explain exactly what Galileo saw on that fateful day in 1997, revealing that the spacecraft likely got sprayed with water shooting from Europa when it made a flyby of the moon.
That said, the new study doesn't necessarily confirm the existence of a plume, either.
"I personally think that this [the new study] is strong circumstantial evidence that a plume could have been present at Europa 20 years ago, when this flyby took place," Cynthia Phillips, a NASA researcher whose work focuses on Europa, said via email.
"The Hubble observations are circumstantial evidence that plumes could have been present more recently, starting in 2012. Taken together, I still don’t find this definitive proof that a plume on Europa does exist – but it’s certainly possible," Phillips, who wasn't involved with the new study, added.
Signs of life
It's not unheard of that an icy moon in distant space would have water shooting out from it. The Cassini mission caught sight of plumes erupting from Saturn's moon Enceladus.
The only surefire way to find out if Europa does have plumes erupting from it is to send another mission there to observe and even sample the water.
"To detect a plume for certain, we’ll have to return to the Jupiter system, and NASA’s Europa Clipper spacecraft, currently in development, will do just that," Phillips said.
"If plumes do exist on Europa, Europa Clipper will be able to fly through them and study the chemical properties of the material erupted from the surface."
Sampling the water possibly eruption from Europa could have huge implications for our understanding of the world.
Researchers have long-thought that Europa's sea could play host to microbial life, but unless we get a sample of that water and analyze it, we'll never know if it's actually habitable.
If some of the water from Europa's interior can be collected without actually landing on the moon, it could be a boon for exploration in that it's much easier to send a spacecraft on a flyby mission than to actually land something on the surface of the world.
However, according to Phillips, that kind of mission also has its limitations when it comes to discerning habitability.
"It’s unlikely that plumes, if they exist, come directly from a subsurface ocean layer, since the surface ice layer is thought to be kilometers thick. It’s much more likely that any plumes would come from a water pocket or 'lake' contained within the ice shell, closer to the surface," Phillips added.
"So, if plume material is collected, it may not be a direct sample of the ocean layer, but will still yield important insights into the composition of materials within Europa, and the potential for habitability – could there be environments on Europa where life could survive?"