Hubble telescope ramps up search for Europa’s watery plumes

Observations in the next 8 months aim to confirm that Jupiter’s icy moon spews water from its south pole

illustration of Jupiter and Europa

LITTLE MOON, BIG WORLD  Watching the tiny ice moon Europa cross in front of Jupiter helped astronomers reveal Europa’s watery plumes. This artist’s impression superimposes real visible images of Jupiter and Europa with ultraviolet data from the Hubble Space Telescope showing the plumes (blue).

NASA, ESA, and M. Kornmesser

OXON HILL, Md. — Astronomers may soon know for sure if Europa is spouting off. After finding signs that Jupiter’s icy moon emits repeating plumes of water near its southern pole, astronomers using the Hubble Space Telescope hope to detect more evidence of the geysers.

“The statistical significance is starting to look pretty good,” astronomer William Sparks of the Space Telescope Science Institute in Baltimore says. He presented preliminary results on the hunt for the plumes at a meeting of the American Astronomical Society on January 9.

Sparks’ team started observing Europa on January 5, hoping to catch it passing in front of Jupiter 30 times before September. Hubble can detect active plumes silhouetted against background light from Jupiter. If the plume repeats as often as it seems to, “it’s essentially a certainty we’ll see it again if it’s real,” Sparks said.

Europa probably hosts a vast saltwater ocean buried under a thick icy shell. In 2012, astronomers using Hubble spotted high concentrations of hydrogen and oxygen over Europa’s southern hemisphere — signs that Europa was spitting water into space (SN: 1/25/14, p. 6). Later efforts to find those signs using the same technique yielded nothing.

But using Jupiter as a backdrop for the plumes, Sparks and his colleagues spotted several eruptions (SN Online: 9/26/16) — once in March 2014, again in February 2016 and possibly also in March 2017, Sparks said.

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Maps of Europa’s heat and ionosphere made by the Galileo spacecraft in the 1990s show the plumes’ location was warmer than the surrounding ice. It also had an unusually high concentration of charged particles, perhaps the result of water splitting into hydrogen and oxygen. Both observations support the idea that some ocean is escaping at that spot.

“If it’s a coincidence, it’s a hell of a coincidence,” Sparks says.

Editor’s note: This story was updated January 19, 2018, to clarify that the existence of Europa’s ocean has yet to be confirmed.

Lisa Grossman is the astronomy writer. She has a degree in astronomy from Cornell University and a graduate certificate in science writing from University of California, Santa Cruz. She lives near Boston.

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