From Scientific American:
“If there are plumes emerging from Europa, it is significant,” says study lead William Sparks, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland. “Because it means we may be able to explore that ocean for organic chemistry or even signs of life without having to drill through unknown miles of ice.”
Using Hubble’s Space Telescope Imaging Spectrograph (STIS), Sparks and his team observed Europa 10 times between late 2013 and early 2015 as it crossed the face of Jupiter. Watching in ultraviolet light, in which Europa’s icy surface appears very dark, they looked for shadows of the plumes backlit against Jupiter’s bright, smooth cloudscapes. Three times, painstaking analysis and image processing unveiled what looked like ultraviolet shadows soaring over the southern edge of Europa’s silhouette. If they were plumes, they would contain an estimated few million kilograms of material and reach about 200 kilometers above Europa’s surface.
This is not the first time scientists have spied plumes on Europa. Lorenz Roth, an astronomer now at the Royal Institute of Technology in Stockholm, led a team of researchers who glimpsed what could be a single similarly sized and located plume in 2012. Those findings, reported in Science in 2013, also used Hubble’s STIS instrument. But instead of glimpsing shadows, the findings recorded the ultraviolet emission near Europa’s south pole of what could have been hydrogen and oxygen—exactly what would be produced by a plume of water vapor dissociating into its constituent atomic elements as it is bombarded by particles trapped in Jupiter’s powerful magnetic field.
Afterward, however, the putative plumes observed by Roth’s team vanished, failing to manifest in archival data or in every new search by other telescopes—until now. Perhaps, some thought, the plumes only appeared when Europa reached the farthest edge of its orbit, where the collective …