All those worlds may be ours except Europa but that doesn’t make the ice-covered moon of Jupiter any less intriguing. Beneath Europa’s crisscrossed crust lies a tantalizing ocean somewhere in the neighborhood of 100 kilometers deep—which adds up to more liquid water than on the entire surface of the Earth. Liquid water plus a heat source(s) to keep it so plus the organic compounds necessary for life…well, you know where the thought process naturally goes from there.
And, like Saturn’s much smaller but similarly ice-covered moon Enceladus, Europa could have geysers spraying its internal water out into space. The existence of such plumes has been hypothesized and hinted at by various studies, most recently by the Hubble Space Telescope, but not yet directly observed in action (like Cassini did with Enceladus) nor confirmed to be from fissures connected to its global subsurface ocean (as opposed to being from surface material.) But researchers keep looking for clues about what’s inside Europa, and now a team of scientists has used data from NASA’s Galileo mission to collect further evidence that Europa is—or at least was on Jan. 3, 2000—spraying its ocean into space.
From the European Space Agency (ESA):
Scientists are keen to explore beneath Europa’s thick blanket of ice, and they can do so indirectly by hunting for evidence of activity emanating from below. A new study, led by ESA research fellow Hans Huybrighs and published in Geophysical Research Letters, did exactly this. Building on previous magnetic field studies by Galileo, the simulation-based study aimed to understand why fewer than expected fast-moving protons – which are subatomic particles with a positive charge – were recorded in the vicinity of the moon during one of the flybys of the moon performed by the Galileo probe in the year 2000.
Researchers initially put this down to Europa obscuring the detector and preventing these usually abundant charged particles from being measured. However, Hans and colleagues found that some of this proton depletion was due to a plume of water vapour shooting out into space. This plume disrupted Europa’s thin, tenuous atmosphere and perturbed the magnetic fields in the region, altering the behaviour and prevalence of nearby energetic protons.
Scientists have suspected the existence of plumes at Europa already since the times of the Galileo mission, however indirect evidence for their existence has only been found in the last decade. Excitingly, if such plumes are indeed present, breaking through the moon’s icy shell, they would offer a possible way to access and characterise the contents of its subsurface ocean, which would otherwise be hugely challenging to explore.
Lights in the Dark 
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