- NASA/ESA/K. Retherford/SWRI
Jupiter’s moon Europa – a giant ice ball thought to hide twice as much liquid water as there is on Earth – just became an even hotter target in the search for aliens.
Scientists on Monday unveiled new photographs from NASA’s Hubble Space Telescope, and they likely show “fingers” of water vapor squirting out of Europa’s hidden ocean and into space.
The grainy Hubble photos, taken in 2014, suggest water plumes sprayed 125 miles into space on at least three occasions over 15 months, then rained back down on the surface.
If true, this would be Hubble’s second time catching Europa’s water plumes since 2012.
Water vents would also make Europa, which is about the size of Earth’s moon, an even more irresistible place to look for signs of extraterrestrial life.
“In a future mission, we could fly through those plumes and tell a lot about the chemistry and nature of the surface” and possibly a liquid ocean below, Bob Pappalardo, a planetary scientist at NASA’s Jet Propulsion Laboratory who wasn’t involved in the work, told Business Insider – all without having to drill through the moon’s miles-thick ice shell.
But secretive water worlds like Europa are not alone; Enceladus around Saturn also sprays out water, and so does Neptune’s moon Triton, likely because they all hide giant, globe-spanning oceans.
“A decade or so ago, we had no idea there might be several global oceans within our solar system. Now that’s becoming generally accepted,” Pappalardo said. “Satellite oceans may be the most common habitats for life that exist in the universe.”
However, Pappalardo – and even the researchers behind a new study of Hubble’s images, which will be published in The Astrophysical Journal – could not say the photos prove the existence of water plumes at Europa.
Seeing water plumes from 500 million miles away
Two of the best Hubble photos show why the scientists are hesitant to confirm what they see are water jets:
- Hubble/NASA/STScI/Business Insider
Those blotchy “dark fingers,” circled in red, are the suspected plumes.
Why are the photos so grainy and difficult to make out? It boils down to Hubble’s capabilities, plus what the telescope took pictures of.
Hubble was about 400-500 million miles away from Jupiter at the time, and it was taking pictures of Europa’s backlit silhouette as it moved across the gas giant’s surface:
- NASA/ESA/W. Sparks (STScI)
During a press teleconference on Monday, William Sparks, an astronomer at the Space Telescope Science Institute, said “we are really working at the limits of Hubble’s unique capabilities.”
“Trying to just image Europa with the Hubble Space Telescope clearly from Earth is challenging,” Pappalardo said. “Trying to image the [silhouette] of a plume, via the light of Jupiter, is a remarkably hard feat. There’s essentially a lot of noise in the system.”
NASA’s press materials lean heavily on the word “if” as well (our emphasis added):
“These plumes, if they do indeed exist, may provide another way to sample Europa’s subsurface,” Geoff Yoder, the associate administrator for NASA’s Science Mission Directorate, said in the space agency’s release.
Another “if” regarded the moon’s water-enriched atmosphere: “If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette,” Sparks said in the release.
When we pressed Pappalardo for his opinion, he also expressed caution.
“I’m not pretty damn sure they are there. I’m not pretty sure they’re not there. Maybe I’m a little more of a skeptic, or need a higher threshold of proof,” Pappalardo said. “But it’s certainly plausible and reasonable there are plumes there that are active and sporadic.”
The next mission to Europa
Despite his inherent skepticism about the evidence, Pappalardo and other researchers hope water plumes at Europa do exist.
“We know there are [vapor] plumes out at Neptune’s moon Triton, and Enceladus at Saturn,” he said. “If they’re at Europa, too, they’d be a relatively common thing. It becomes something that icy worlds just do – they vent their interiors out into space.”
NASA’s James Webb Space Telescope, scheduled to launch in 2018, might have the instrumentation to analyze the chemistry of such plumes, if they do exist around Europa.
Pappalardo said another way to analyze them is to fly a robot right through the vapor: In particular the $2 billion Europa Clipper mission, also called the Europa Multiple-Flyby Mission, a project that he is a member of.
By flying a robot through watery plumes, scientists might detect molecules that support life’s existence in a subsurface ocean.
Some researchers also think it may be possible to compare the carbon, nitrogen, oxygen, and other chemicals in a plume to “default” levels seen in asteroids, which were formed at the dawn of the solar system – and ask if life is manipulating the chemistry there, or at least did so in the past.
“I really don’t know the odds, but the discovery of life elsewhere in our solar system would be so significant, we have to find out,” Pappalardo said. “If there’s life at Europa, it’d almost certainly be an independently evolved form of life. Would it use DNA or RNA? Would it use the same chemistry to store and use energy? Discovering extraterrestrial life would revolutionize our understanding of biology.”
He added: “And at the same time we’d know we’re not alone in the universe.”
Should we discover a habitable ocean with the next Europa mission, which is scheduled to launch in 2022, or even hints of life, researchers are ready to up the ante.
Fans of Europan exploration would like to make happen an ambitious scheme to sink a nuclear-powered robot below the ice and directly seek out signs of life.
It might be more possible than we might expect, too, since a growing line of research increasingly shows Europa is not a cold, dead world: Its surface is likely roiling with giant ice slabs that are cracking, breaking up, sinking, and melting.
In the chaos, there may be a shortcut to explore the depths below.