Jupiter’s Moon Europa Might Glow in the Dark

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You’ve probably seen numerous photos and renderings of Europa, its icy surface covered in reddish streaks. However, those images are all captured with illumination from the sun. A new analysis from NASA’s Jet Propulsion Laboratory (JPL) suggests that there might be something interesting on the Jovian moon’s dark side. The intense radiation bombarding Europa might make it glow in the dark, and that could help scientists learn more about the moon’s ice sheets and the ocean below. 

Europa is a little smaller than Earth’s moon, making it the smallest of Jupiter’s four Galilean moons, all of which are so-named in honor of their discoverer, the pioneering astronomer Galileo Galilei. Modern astronomers became increasingly interested in Europa when the missions like Voyager revealed the cracked surface and dark lineae. Scientists speculated that Europa had a liquid ocean under the surface, kept warm by tidal heating from Jupiter’s immense gravitational effects. The thick ice sheets hide the interior from direct analysis, but the new JPL study makes the case that the glowing ice could offer some important clues. 

Initially, the team was interested in studying the effects of high-energy radiation on organic compounds under the ice. To test this, JPL scientists built a unique instrument that was clearly named specifically to have a really cool acronym: the Ice Chamber for Europa’s High-Energy Electron and Radiation Environment Testing (ICE-HEART). They took ICE-HEART to a high-energy electron beam facility where they could blast it with radiation similar to what you’d find in space near Jupiter, but the effects of that radiation were unexpected. 


Europa’s dayside with lineae visible.

ICE-HEART was designed to replicate the various types of ice present on Europa’s surface — sodium salts, magnesium salts, and so on. During the experiments, the team noted that not only did the samples glow, but they also glowed in distinct spectra based on the salt composition. This could mean that Europa’s night side looks like a faintly glowing patchwork (see above), and the pattern could be of note. “If Europa weren’t under this radiation, it would look the way our moon looks to us – dark on the shadowed side,” says lead author Murthy Gudipati. “But because it’s bombarded by the radiation from Jupiter, it glows in the dark.”

The team speculates that water from the suspected sub-surface ocean would percolate to the surface over time. So, the glowing on the surface can tell us about what’s underneath, and we might be able to characterize the surface simply by observing its light spectrum. “It’s not often that you’re in a lab and say, ‘We might find this when we get there,’” Gudipati said. “Usually it’s the other way around – you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that’s what science is about.” 

Our next chance to test this hypothesis in real life may come with the Europa Clipper mission, which will launch in 2024. After arriving in orbit of Europa in 2030, it will conduct multiple flybys that give it the opportunity to check for any possible glow in the dark effects.

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