Now you see it, now you don't. Europa's 200-kilometre-high water jets may have been downgraded from major discovery to major mystery. Follow-up searches have yet to see the geysers again, while older observations don't seem to support their existence. Some people are now wondering if the jets are far rarer than expected – or if they were ever there to begin with.
"It's a real puzzle now," said Donald Shemansky of the University of Southern California in Los Angeles, who presented the analysis of spacecraft data at the American Geophysical Union conference in San Francisco on 18 December that contradicted the idea of regularly erupting plumes.
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