December 12, 2013 | David F. Coppedge

Europa Joins the Geyser Club

Hints of watery plumes have been detected on Europa – like Enceladus, at its south pole, too.

Judging from its surface, Europa should have activity.  It resembles the known active surface of Saturn’s geysering moon Enceladus.  Europa has numerous ridges bounded by parallel mounds that suggest water from its inferred subsurface ocean has gushed out of linear vents many times.  No activity has been detected, though, till now.  The Hubble Space Telescope detected blogs of hydrogen and oxygen near the south pole, best explained as plumes of water vapor.  Planetary scientists are excited (see Hubble Site, Jet Propulsion Laboratory, Nature News, Science Now, BBC News, National Geographic, New Scientist and Space.com).

The data are indirect and preliminary.  No plumes have been imaged; only concentrations of hydrogen and oxygen that suggest ionization of water has occurred.  The concentration of hydrogen, moreover (imaged in ultraviolet light) varied during the orbit, becoming strongest when Europa was farthest from Jupiter.  Planetary scientists announcing the find at the AGU meeting said the data are best explained by watery plumes 200 km high (125 miles) – higher than Mt. Everest and higher than Io’s volcanoes, but not as high as Enceladus’s geysers.  According to the estimates, 7 tons of material is escaping per second (most of it falling back on the surface), at supersonic speeds of 700 meters per second.  As for a mechanism, “The frictional heat of ice rubbing against itself might melt parts of the icy crust and feed the plumes,” Nature News said.  If so, the material does not necessarily tap into the subsurface ocean.

It’s possible many more plumes exist.  The south polar plumes were best seen against the blackness of space; others would have been harder to discern against the bright surface.  This initial observation is sure to be followed up by more attempts.  Since no proposed Europa missions could reach the moon till the 2020’s or 2030’s, most observations will require Earth-based observations, although America’s Juno mission to Jupiter (arriving in 2016) might be able to sense the plumes remotely.

None of the articles addressed the age question.  All of them except Science Now suggested that the presence of water might mean life exists there.

Update 12/18/14: Cassini scientists could not find signs of plumes in their data from the spacecraft’s flyby of Jupiter in 2001 (see JPL press release).  Either the plumes are intermittent, or the Hubble Space Telescope saw something else.  The Hubble team is going to look some more.

Since the observations are indirect, it will take time to corroborate the conclusions that water or water vapor is indeed erupting at Europa, but the possibility is intriguing and will be fun to watch.  It should be quite a surprise to those believing the moons are billions of years old to find another one popping off – at its south pole, too, just like on Enceladus.  What is it about south poles that generates activity?  One would expect the equators to be the most active.  The active zones may just be the latest in a long series of eruptions that produced the ridges on both moons.  It shouldn’t be too hard to estimate upper limits for activity.  Given that small bodies should freeze solid in short order, it’s likely the scientists will struggle now with Europa’s activity like they have with Enceladus, Io, Titan, Triton, the Moon, Earth, etc.

Science reporters are so predictable.  They completely ignore the age issue.  Instead, hearing the word “water,” they go into robotic mode.  They turn off their minds and quack the L-word Life like programmed rubber ducks (see hydrobioscopy in the Darwin Dictionary).

 

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