This artist's impression shows the water vapour plumes from Europa's south pole.Pointing the powerful Hubble Space Telescope at the planet Jupiter and its icy moon Europa, scientists have observed evidence of what looks to be geysers of water vapour shooting from Europa's surface.
The smallest of Jupiter's 'Galilean moons', Europa's entire surface is hidden away under a thick layer of ice and what scientists believe is a subsurface ocean, possibly kept warm by tidal forces from Jupiter's immense gravitational pull. Up until now, there's been no direct evidence of any liquid water, so whether or not that ocean under the ice exists has been up for debate. However, these observations show strong support for the idea that the ocean is there.
The images taken by Hubble were from November and December of 2012. In the November observations, when Europa was closer to Jupiter in its orbit, no plumes or geysers were seen. In December, when Europa was further away from the planet, the telescope spotted the tell-tale sign of water vapour, based on the ultraviolet light emissions from the moon's south pole.
"By far the simplest explanation for this water vapor is that it erupted from plumes on the surface of Europa," said Lorenz Roth, the lead author of the study from the Southwest Research Institute, according to a statement. "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."
The HubbleESA group put together a cool-looking artist's impression video to show what the water vapour plumes look like, shining away in ultraviolet light.
According to the researchers, the plumes appearing when the moon is further from Jupiter supports the idea that tidal forces from Jupiter's gravity cause the surface cracks in the Europa's icy shell to squeeze shut when the moon is closer in and are relaxed and open when it's further away. These relaxed and open cracks would allow water from the subsurface ocean to be squeezed up through the cracks and into space.
Similar water vapour plumes have been seen streaming off of Saturn's icy moon Enceladus. However, the difference here is that Enceladus' plumes escape into space, whereas Europa's gravitational pull is strong enough that any water vapour being blasted into space by a geyser will reach about 200 kilometres off the surface before the moon's gravity pulls it back down. The researchers believe that this could leave bright regions near the poles, as the water vapour freezes as it settles onto the ice surface.
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This is a very cool discovery, and it gives hope that we won't necessarily have to slam large impactors into the Europa surface to really explore whether there could be an ocean under the surface layer of ice. These plumes, if confirmed, could be a way to indirectly probe the interior to see what conditions are like there. Could there be life in that ocean? If temperatures are warm enough in the interior to maintain a substantial layer of liquid water, it's possible. Also, recent findings say that the asteroid that killed the dinosaurs may have launched enough matter from Earth far enough out into space that around 20 tons of that matter could have impacted on Europa, potentially delivering key building blocks of life to the icy moon.
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