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Europa plumes
These composite images show a suspected plume of material erupting two years apart from the same location on Jupiter’s icy moon Europa. Both plumes, photographed in ultraviolet light by Hubble, were seen in silhouette as the moon passed in front of Jupiter. (NASA / ESA / STScI / USGS)

Saturn’s moon Enceladus wasn’t the only ice-covered world making waves today: Scientists say Europa, a mysterious moon of Jupiter, has shown fresh signs of watery plumes that may hint at a habitable environment beneath the ice.

Last year, the Hubble Space Telescope picked up observations of what appeared to be a plume of watery material, emanating from the same area where a plume was spotted in 2014.

The most recent plume rises about 62 miles (100 kilometers) above Europa’s surface, which is twice as high as the earlier plume.

The source of the activity is an unusually warm region of ice that appears to be crisscrossed by cracks, based on pictures captured in the late 1990s by NASA’s Galileo spacecraft.

Europa hot spot
The green oval highlights the plumes Hubble observed on Europa. The area also corresponds to a warm region on Europa’s surface. The map is based on observations by the Galileo spacecraft. (NASA / ESA / STScI / USGS)

“The plumes on Enceladus are associated with hotter regions, so after Hubble imaged this new plume-like feature on Europa, we looked at that location on the Galileo thermal map. We discovered that Europa’s plume candidate is sitting right on the thermal anomaly,” William Sparks of the Space Telescope Science Institute said in a news release.

Sparks led the Hubble plume studies in both 2014 and 2016, and he’s the lead author of a report on the observations published today in the Astrophysical Journal Letters.

Taken together, the evidence suggests that water from an ocean hidden beneath Europa’s ice occasionally spews out into space through the cracks. The area may be warmed up as water passes through the cracks, or as the watery mist falls back to the surface and causes more heat to be retained.

As is the case with Enceladus, such activity on Europa could point to hydrothermal processes and a potentially habitable environment deep beneath the ice.

Whatever is going on down there, it doesn’t seem to be going on continuously. Repeated observations in ultraviolet light, using Hubble’s Space Telescope Imaging Spectrograph, haven’t always turned up evidence of plumes.

Sparks and his team are continuing to use the STIS instrument to keep watch for more plumes. And NASA’s Europa Clipper spacecraft, which is currently in its design phase, will have better instruments for observing the moon’s hot spots and any watery plumes that crop up.

Europa Clipper is due for launch in the 2020s.

“If there are plumes on Europa, as we now strongly suspect, with the Europa Clipper we will be ready for them,” Jim Green, director of planetary science at NASA Headquarters, said in today’s release.

In addition to Sparks, the authors of “Active Cryovolcanism on Europa?” include B.E. Schmidt, M.A. McGrath, K.P. Hand, J.R. Spencer, M. Cracraft and S.E. Deustua. For more about the search for signs of water in our solar system and beyond, check out NASA’s online presentation on “Ocean Worlds.”

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