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WASHINGTON, Sept. 26 (Xinhua) -- U.S. space agency NASA said Monday its Hubble space telescope has imaged what may be water vapor plumes erupting off the surface of Jupiter's icy moon Europa, a finding that may allow scientists to much more easily study whether life exists in the moon's hidden subsurface ocean.
"For a long time humanity has been wondering whether there is life beyond Earth ... Europa might be such a place," Paul Hertz, director of the astrophysics division at NASA, told reporters at a teleconference.
"Today's results increase our confidence that water and other materials from Europa's hidden ocean might be on the surface of Europa and available for us to study without landing and digging through those unknown miles of ice," Hertz said.
The new discovery, to be published in the Sept. 29 issue of The Astrophysical Journal, attracted widespread attention after NASA released a statement last week announcing a news conference for Monday on evidence of "surprising activity" on Europa.
The U.S. space agency later clarified via Twitter: "Spoiler alert: NOT aliens!"
Europa, one of Jupiter's largest moons, is slightly smaller than Earth's moon. It has a huge global ocean containing twice as much water as Earth's oceans, but it is protected by a layer of extremely cold and hard ice of unknown thickness.
In the new study, the team, led by William Sparks of the Space Telescope Science Institute in Baltimore, Maryland, observed "finger-like projections" while viewing Europa's limb as the moon passed in front of Jupiter.
The original goal of the team's observing proposal was to determine whether Europa has a thin, extended atmosphere, but the team also realized if there was water vapor venting from Europa's surface, this observation would be an excellent way to see it.
"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.
"And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter."
In 10 separate occurrences spanning 15 months, the team observed Europa passing in front of Jupiter and saw what could be plumes erupting on three of these occasions.
The finding followed a similar discovery in 2012, in which a team led by Lorenz Roth of Southwest Research Institute detected evidence for water vapor erupting from the frigid south polar region of Europa and reaching more than 160 kilometers into space.
Although both teams used Hubble's Space Telescope Imaging Spectrograph instrument, each used a totally independent method to arrive at the same conclusion, the space agency said.
"Observations thus far have suggested the plumes could be highly variable, meaning that they may sporadically erupt for some time and then die down," it said.
"For example, observations by Roth's team within a week of one of the detections by Sparks' team failed to detect any plumes."
If confirmed, Europa would be the second moon in the solar system known to have water vapor plumes. In 2005, NASA's Cassini orbiter detected jets of water vapor and dust spewing off the surface of Saturn's moon Enceladus.
Scientists may use the infrared vision of the James Webb Space Telescope, which is scheduled to launch in 2018, to confirm venting or plume activity on Europa, NASA said.
The U.S. space agency also said it's formulating a mission to Europa with a payload that could confirm the presence of plumes and study them from close range during multiple flybys.
"Life, as we know it, requires liquid water, and Europa's on NASA's hit list because it is one of the most likely places to find water in our solar system," Rice University planetary geophysicist Adrian Lenardic, who was not involved in the study, said in comments on Hubble's new finding.
"If you find a place with liquid water, the potential that it could host life, be it probably little bacteria at this point in time, increases. And that's the excitement. That's the draw."
