NASA has announced that it has found evidence of water plumes erupting from the surface of Jupiter’s moon Europa, using images taken by the Hubble Space Telescope, hinting that the Jovian moon’s subsurface oceans — oceans that scientists consider to be a good candidate as a host for extraterrestrial life — may be more accessible than what was once thought.

Previous hints of what may have been geyser eruptions on Europa were seen in 2005 as the Cassini orbiter flew by on its way to Saturn, and again in 2012 more evidence was spotted by Hubble. This prompted the current study, where Europa was imaged by Hubble as it made its transit across the face of Jupiter. The researchers found that many of the images showed what appeared to be clouds of material high above the surface near Europa’s south pole that were occulting the ultraviolet light being emitted from Jupiter in the background.

NASA is cautioning that what they are seeing is not definitively water geysers — a proper spectrographic study still needs to be done to determine the cloud’s chemical composition — but that ejected water is the best candidate to explain their observations.

Europa receives a great deal of gravitational influence from Jupiter, creating strong tidal forces within the icy moon, forces that are theorized to keep the subsurface water in a liquid state. The plumes appear to be ejected to an altitude of 201 km (125 miles), then settle back down to the moon’s surface, possibly leaving bright features on the surface ice.

This finding is important in that it offers further evidence of Europa’s subsurface ocean: being between two to three times the size of Earth’s oceans, it is possibly the largest in the solar system. This also means that future missions to the ice-encrusted moon might not have to drill through miles of ice to reach this all-important water to sample it.

“By far the simplest explanation for this water vapor is that it erupted from plumes on the surface of Europa,” the study’s lead author Lorenz Roth, of San Antonio’s Southwest Research Institute. "If those plumes are connected with the subsurface water ocean we are confident exists under Europa’s crust, then this means that future investigations can directly investigate the chemical makeup of Europa’s potentially habitable environment without drilling through layers of ice. And that is tremendously exciting."

Because of the presence of this large body of liquid water, Europa is considered to be an important candidate in the search for extraterrestrial life within our solar system. NASA is currently planning two missions to Europa sometime in the 2020s, starting with an orbiter that will scan the moon, and followed up a few years later with a landing craft. 

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