May 15, 2018 | David F. Coppedge

Europa May Be Another Geyser Moon

A re-assessment of data from the Galileo spacecraft appears to confirm suspected eruptions from the surface of Europa, Jupiter’s icy moon.

The “active body club” may have gained a new member. The earth and Io have volcanoes; Triton has nitrogen eruptions, and Enceladus famously stunned Cassini scientists who witnessed over 100 geysers shooting icy particles and dust out of cracks in its south pole. Is Europa bringing the count of active bodies to five? (Note: Mercury, Venus, Mars, possibly Pluto, and even the moon have extinct volcanoes, but only a few bodies are actively erupting now.)

Europa (top) compared to Earth and Mars.

The Hubble Space Telescope caught hints of plumes a few years ago, but confirmation was difficult. The data to clinch it may have been sitting in archives from the Galileo spacecraft (1996-2003). Jet Propulsion Scientist Xianzhe Jia now believes he found the “smoking gun,” so to speak: variations in Europa’s induced magnetic field. A JPL press release on Monday shared reasons for thinking Europa may also be erupting:

Data collected by NASA’s Galileo spacecraft in 1997 were put through new and advanced computer models to untangle a mystery — a brief, localized bend in the magnetic field — that had gone unexplained until now. Previous ultraviolet images from NASA’s Hubble Space Telescope in 2012 suggested the presence of plumes, but this new analysis used data collected much closer to the source and is considered strong, corroborating support for plumes. The findings appear in Monday’s issue of the journal Nature Astronomy.

An embedded video clip in the article shows animations of what the plume might look like. Jia used newer techniques of data analysis to make a convincing case. “The data were there, but we needed sophisticated modeling to make sense of the observation,” he said. His results show not only evidence that the plume is real, but that the spacecraft actually flew through it.

As could be expected, the press release plays up the possibility of life. Europa is believed to have a subsurface ocean that accounts for the induced magnetic field. If the moon is erupting particles through its icy crust, scientists are imagining that the plume could serve up organisms, making detection easier than having to dig down through the icy crust.

“If plumes exist, and we can directly sample what’s coming from the interior of Europa, then we can more easily get at whether Europa has the ingredients for life,” Pappalardo said. “That’s what the mission is after. That’s the big picture.”

A mission called the Europa Clipper may be called on to look for not Europeans, but Europans. One letter makes a big difference.

Speaking of magnetic fields, there’s a new paper in Geophysical Research Letters about Ganymede, Europa’s neighbor, the largest moon in the solar system. Galileo mission scientists were surprised to find years ago that Ganymede has an intrinsic (not induced) magnetic field. Most of the paper concerns details of the magnetic field, but here’s part of the “plain language summary”—

NASA’s Galileo spacecraft made the first ever flyby of Jupiter’s largest moon, Ganymede, on 27 June 1996, discovering that it is the only moon known to generate a magnetic field. As at Earth, Ganymede’s magnetic field projects a magnetic bubble around it called a magnetosphere. Galileo carried a package called the Plasma Subsystem (PLS) that was designed to measure charged particles. Although PLS collected data during this first flyby, the results were never published. Resurrecting the original flight software, we processed these data and present them here for the first time, permitting us to go back with a fine detail brush and fill in some of the structure of this complex and exotic magnetosphere. Charged water‐based particles were observed escaping from the moon, having been blasted off the icy surface by an energetic rain of particles from Jupiter.

The scientists also describe Ganymede’s auroral zones, its ionosphere and other manifestations of a magnetic field. Since magnetic fields decay with time, it remains a puzzle that a body this size would have a magnetic field. The comparably-sized moon Titan does not.

Planetary scientists need to kick the hydrobioscopy habit and explain how little Euroopa could be erupting material into space for billions of years. Enceladus is even smaller. Another paper in Icarus was just published that tried to keep Enceladus going, but admitted that “Explaining Enceladus’ endogenic power requires ocean and shell thicknesses that are smaller than the expected values.” Deal with that question instead of doing a sidestep with a distraction about life.







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