Washington: In a surprise find, astronomers using NASA's Hubble Space Telescope have spotted water vapour plumes erupting off the surface on Jupiter's moon Europa, suggesting that life may exist in our solar system.
The observation increases the possibility that missions to Europa may be able to sample Europa's ocean without having to drill through miles of ice.
"Europa's ocean is considered to be one of the most promising places that could potentially harbour life in the solar system," said Geoff Yoder, acting associate administrator for NASA's Science Mission Directorate in Washington, DC.
"These plumes, if they do indeed exist, may provide another way to sample Europa's subsurface," Yoder added.
Europa is one of the largest of Jupiter's 67 known moons. In late 2013, the Hubble telescope observed water vapour erupting from Europa, in what was hailed as a atremendously exciting' discovery.
The plumes are estimated to rise about 200 km before, presumably, raining material back down onto Europa's surface.
Europa 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.
The plumes provide a tantalising opportunity to gather samples originating from under the surface without having to land or drill through the ice.
The team, led by William Sparks of the Space Telescope Science Institute (STScI) in Baltimore observed these 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, or exosphere.
"The atmosphere of an extrasolar planet blocks some of the starlight that is behind it," Sparks said.
"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. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter," he explained.
In 10 separate occurrences spanning 15 months, the team observed Europa passing in front of Jupiter. They saw what could be plumes erupting on three of these occasions.
If confirmed, Europa would be the second moon in the solar system known to have water vapour plumes.
In 2005, NASA's Cassini orbiter detected jets of water vapour and dust spewing off the surface of Saturn's moon Enceladus.
Scientists may use the infrared vision of NASA's James Webb Space Telescope, which is scheduled to launch in 2018, to confirm venting or plume activity on Europa.
NASA is also formulating a mission to Europa with a payload that could confirm the presence of plumes and study them from close range during multiple flybys.
"Hubble's unique capabilities enabled it to capture these plumes, once again demonstrating Hubble's ability to make observations it was never designed to make," said Paul Hertz, director of the Astrophysics Division at NASA headquarters in Washington, DC.
The work by Sparks and his colleagues is forthcoming in the Astrophysical Journal.