Forget those cute little star stickers you used to have as a kid (or at least I did), because imagine an entire moon that glows in the night sky, and not because it is reflecting light from our favourite star in the universe. Rudolph’s glowing red nose pales next to this super-shiny moon orbiting a planet in our solar system, its light blue, but with little tinges of green and white. So, what exactly is this curious glowy moon that lights up some lucky planet’s night sky?
That moon is Europa, one of the so called Galilean moons of Jupiter, and its glow-up is, unfortunately, not from some benign cause; rather, it is all down to Jupiter’s radiation. Thanks to Europa’s proximity to Jupiter, this little icy moon “enjoys” a daily, relentless dose of high-energy Jovian radiation on its surface, the consequence being that its night-side would still glow even when facing away from Jupiter, as suggested by a series of lab experiments down by a science research team, with the paper released in November 2020.
Their lab experiment involved blasting Europan ice analogues (i.e. water ice with different compositions of salts) with high-energy electrons, and analysing the results’ various light emissions. They also related their findings back to earlier studies where they had discovered that with increased intensity of high-energy electron bombardment, the greater the spectral (i.e. light) intensity. The light emission was also noticeably stronger in ice containing epsomite, which is a very soft mineral (hardness of 2) with a chemical composition that includes magnesium and sulfate, as well as water. In contrast, samples with sodium chlorate or sodium chloride gave off the least light.
This study has several implications for future research and exploration of this frozen moon with its spectacular glow-up, especially more so with the potential launch of the Europa Clipper spacecraft maybe in the mid-late 2020s. For example, relating back to the amounts of light reflected depending on salt composition, scientists looking at the Europa Clipper’s imagery would be able to note darker patches as likely containing sodium chlorate and/or chloride, and brighter areas likely containing epsomite salts. These observations would be key to furthering whether Europa has the right conditions for life swimming somewhere deep under its icy crust. But, whether or not Europa’s glow could be detected by the space-craft’s cameras, is still yet to be determined or confirmed, but if it could, that could potentially be very breathtaking!
References:
https://www.nature.com/articles/s41550-020-01248-1 Laboratory Predictions for the night-side surface ice glow of Europa, Nature Astronomy, Nov 2020.
https://www.jpl.nasa.gov/news/news.php?feature=7779 Europa Glows: Radiation does a bright number on Jupiter’s Moon. Jet Propulsion Laboratory, NASA. Nov 2020.
http://www.physicsworld.com/a/jupiters-moon-europa-could-glow-in-the-dark Jupiter’s Moon, Europa, could glow in the dark, Physics World, Nov 2020.
https://www.mindat.org/min-1393.html Epsomite, mindat.org
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