Europa, a moon of Jupiter thought to harbor a warm, saltwater ocean sloshing beneath a thick, icy crust, has long been considered one of the best spots in the solar system to look for alien beings.
Now, citing data collected by NASA’s Galileo probe more than two decades ago, scientists report giant jets of water are spouting more than 100 miles off the moon’s surface — adding to evidence that Europa is spewing its contents into space. If the plumes’ existence is confirmed, and they are linked to Europa’s ocean, they could provide a tantalizingly straightforward way to sample the moon in search of signs of life. Rather than land on the surface and drill as much as 15 miles through ice — a feat that has never been achieved even on Earth — a spacecraft could fly through the spray and test its contents.
Researchers are already working on missions to do just that. NASA’s Europa Clipper and the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) are slated to launch in the early to mid-2020s, both armed with high-resolution cameras and a suite of other sensitive instruments.
“The idea that Europa might possess plumes seems to be becoming more and more real, and that’s very good news for future exploration,” said Xianzhe Jia, a space physicist at the University of Michigan and the lead author of the new paper in the journal Nature Astronomy. The results of the Clipper and JUICE missions, he said, “could have huge implications” — nudging us Earthlings closer to understanding whether we are alone.
Scientists have suspected since 2012 that Europa might harbor plumes, after the Hubble Space Telescope observed water vapor spouting above the moon’s frigid south pole. The tallest of the plumes was so powerful that it extended 120 miles above the moon’s surface; Yellowstone’s Old Faithfulreaches only 184 feet.
The interpretation of those images has been debated; the images pushed the limits of Hubble’s sensitivity. Jia had a hunch that, if a plume existed, the spacecraft Galileo in 1997 might have sensed its signatures with its magnetometer and plasma wave instruments. The data did show unusual emissions that could be associated with a high density of charged particles —just what you would expect to find near a speeding jet of salty water. But the environment around the moon is complex — warped by Jupiter’s strong magnetic fields and by Europa’s own atmosphere. So they ran the data through a sophisticated modeling program. “The result came out with very satisfying agreement,” Jia said — scientist speak for “we were right.”
The Clipper mission is projected to arrive at Jupiter around 2030. “If Clipper does end up flying through the plumes and the instruments are able to measure the composition, by analyzing those data we’ll be able to assess whether or not Europa has conditions for life,” Jia said.