Water vapour plumes spotted on Jupiter's moon Europa: NASA

The Hubble Space Telescope has spotted what may be water vapour plumes erupting off Jupiter's moon Europa - believed to be one of the most promising places that could harbour alien life in the solar system, NASA said.
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, from NASA's Science Mission Directorate.
"These plumes, if they do indeed exist, may provide another way to sample Europa's subsurface," said Yoder.

The plumes are estimated to rise about 200 kilometres before 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, NASA said.
The team, led by William Sparks of the Space Telescope Science Institute (STScI) in the US, 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.
Using the same observing method that detects atmospheres around planets orbiting other stars, the team also realised if there was water vapour venting from Europa's surface, this observation would be an excellent way to see it.
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.
This work provides supporting evidence for water plumes on Europa, researchers said.
In 2012, a team led by Lorenz Roth of Southwest Research Institute in the US detected evidence for water vapour erupting from the frigid south polar region of Europa and reaching more than 160 kilometres into space.

Although both teams used Hubble's Space Telescope Imaging Spectrograph (STIS) instrument, each used a totally independent method to arrive at the same conclusion.
Observations thus far have suggested the plumes could be highly variable, meaning that they may sporadically erupt for some time and then die down.
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 vapour plumes.
In 2005, NASA's Cassini orbiter detected jets of water vapour and dust spewing off the surface of Saturn's moon Enceladus.