NASA scientists announced Monday that Jupiter’s moon Europa is spewing out plumes of water vapor off its surface, according to new data collected by the Hubble Space Telescope.
The findings, teased in last week’s announcement, were perhaps not as “surprising” as they were originally billed, but they nevertheless stoke a healthy amount of excitement that Europa could be another habitable world for life outside of Earth — and may already be home to primitive extraterrestrials.
Europa, an icy little rock about the size of Earth’s moon, contains a very intriguing ocean located underneath a several-miles-long layer of ice covering up the surface. Scientists are insanely eager to learn more about the ocean and investigate the potential for the world to host life. It is “a truly compelling astrobiological target in the solar system,” said astronomer William Sparks, an astronomer with the Space Telescope Science Institute in Baltimore and one of the leads of the new findings, to be published in the September 29 issue of the Astrophysical Journal.
Unfortunately, as of now we have yet to study Europa through close observations. The outer layer of ice makes it impossible to learn more about the vast reserves of liquid water swishing around on the planet.
“We’re impatient and we want to study Europa now,” said Paul Hertz, the director of NASA’s astrophysics division.
So Sparks and his team decided to pool their time and effort into maximizing Hubble’s capabilities and finding out whether there’s anything to see from a distance. In 2014, through ultraviolet observations of Europa’s atmosphere using Hubble, the team found evidence of water jets erupting on three different occasions from the icy surface layer and being ejected out into high altitudes.
The results are encouraging for two reasons: “If water vents open in the ice,” said Sparks, “plumes may emerge and rain back down on the surface,” which means that ocean material left over the surface could be directly studied and analyzed without the need to drill down through the thick ice to collect water samples. The vents may also highlight cracks or points in the ice where a drilling rover could have an easier time diving in order to explore the ocean directly.
Unfortunately, there’s a lot of uncertainty behind the results. Sparks emphasized that the new data itself is not definitive proof that Europa has plumes of water. “The Hubble images are working at the limits of its unique capabilities” and measuring the ultraviolet activity at very extreme wavelengths.
It’s also unclear if the plumes really are water and ice, or something else entirely. The most ideal result would be that the water plumes would contain organic chemicals or other materials indicative of biosignatures, or at the very least a habitable environment. However, the plumes might be composed of something entirely different — elements unrelated to water. The only reason the team has hypothesized water is because “That’s what Europa is made of,” said Sparks. Unless there are problems with Hubble’s instruments — which seems low, given the high statistical significance of the results — he does not know of any other natural alternative.
The eruptions on Europa were also observed from the same perspective. This is important because “if the features are real, they have to be intermittent,” said Sparks.
Finding water plumes on another world would not be a first-of-a-kind discovery. Saturn’s moon Enceladus exhibits similar plumes — lending more support to the notion that Europa possesses the same kind of features. “If it works on Enceladus then why not on Europa?” asked Sparks.
The geology of Europa also suggests the plumes could be located in a multitude of sites, according to Britney Schmidt, a planetary science researcher at Georgia Tech. It’s unclear yet exactly what causes the water to ascend to the surface — it could be heat from the sun, or internal volcanism — but that’s a question to be answered on a future mission.
And a future mission to study Europa is already in the planning stages. Curt Niebur, the program scientist for Europa, discussed how effective the upcoming James Webb Space Telescope will be for verifying the UV measurements.
More important, however, will be the Europa Multiple-Flyby Mission, which will launch sometime in the 2020s and conduct multiple swoops around Europa to measure surface data on nine different instruments to better understand what the water vents mean for the prospects of life on the moon. In addition, the probe will carry “compositional instruments to ingest samples of the [plume] material,” said Niebur, and analyze it directly.
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