The discovery, set to be published in the Astrophysical Journal, whets the appetite of scientists who want to investigate whether this distant world could potentially harbor life.
"If there are plumes emerging from Europa, they're significant because it means we may be able to explore [its ocean] for organic chemicals or even signs of life, without having to drill through unknown miles of ice," team leader William Sparks, an astronomer at the Space Telescope Science Institute, said at a news briefing Monday.
Europa's ocean holds about twice as much water as Earth's oceans do. Like Saturn's much-smaller moon Enceladus, it is one of the solar system's frigid water worlds, both of which may hold the right chemical ingredients for life to theoretically exist beneath their surface. Scientists have already found evidence for hydrothermal vents on Enceladus, which on Earth provide fertile ground for deep-sea microbial life.
The plumes that may give these ocean worlds away are well documented on Enceladus, spewing from "tiger stripe" cracks that are squeezed and stretched by tidal forces. NASA's Cassini spacecraft has even flown through the plumes, sampling its contents. On Europa, however, trying to find those plumes is much more of a challenge, scientists said.
"It's covered with ridges and fractures, much like a tectonic yarn ball," Britney Schmidt, a planetary scientist at the Georgia Institute of Technology who was not involved in the findings, said at the news briefing.
"Whereas on Enceladus the geology makes it a little bit obvious where the activity has been, on Europa there's activity everywhere, which could lead to plumes or could muddy the interpretation," Schmidt said.
In 2012, a team led by Lorenz Roth of the Southwest Research Institute found signs of water geysering out near the moon's southern pole. Now, Sparks' team found these plumes by using essentially the same method that astronomers use to find planets around far-off stars.
As a planet transits in front of its star, a tiny slice of starlight will filter through the little world's atmosphere. Scientists can look at what's missing in that sliver of light to determine the composition of the planet's atmosphere.
Jupiter doesn't make its own light, but it reflects quite a bit of the sun. Scientists realized they could study Europa's atmosphere by watching how Jupiter's reflected ultraviolet luminescence filtered through it.
Over the course of 15 months, the scientists observed Europa passing in front of Jupiter 10 times. And on three of those occasions, they saw plumes of what appears to be water vapor erupting from the surface.
The findings are good news for researchers working on NASA's planned mission to Europa, scientists said.
"If nature's being kind and some of this water's being vented into the outer regions where spacecraft can fly by and make measurements, that would be spectacular," said Adrian Lenardic, a planetary geologist at Rice University who was not involved in the study. "And I think that's one of the next things that is in the plans for the future Europa mission."
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Sept. 27, 1:05 p.m.: This story was updated with additional information from Britney Schmidt.