The only celestial object that has been observed to glow on its nighttime side has been Earth. Yet, even this light does not come from a natural, geological source, but from human activity. We create so much light that it is visible from outer space. Now, scientists think that we might have a glowing companion, and that the light it emits could tell us about the make-up of its icy surface.

Europa, one of Jupiter’s moons, has a frigid surface covered with ice. As it orbits Jupiter, which has the largest magnetic field of any planet in our solar system, it is relentlessly bombarded with radiation. Scientists believe that Europa’s surface, after interacting with these high-energy particles, could emit light, causing the moon to shine. To find out, Gudipati and colleagues at NASA’s Jet Propulsion Laboratory recreated the surface conditions of Europa based on our current knowledge of its composition. Observations using Hubble and Earth-based telescopes have shown that the moon contains minerals such as Epsom and sea salt. When bombarded with high-energy electron radiation, the scientists observed a glow coming from their surface recreations. The strength and color of the light depended on the exact chemical composition, and ranged from blue and green to white.

Though Europa’s frigid surface is covered in ice, underneath it, scientists predict it to have a liquid ocean, heated by the moon’s core. This ocean could be habitable and even house microbial life. For this reason, Europa has garnered much attention, yet its composition has remained elusive, and thus also its habitability. Observing the properties of Europa’s glow could reveal the exact make-up of its surface, and help us understand if the moon is truly suitable for life. NASA hopes that the spacecraft Clipper, which will perform close fly-bys of Europa, will be able to capture its night glow and begin to answer these questions.

Murthy S. Gudipati, the corresponding author of the Nature Astronomy paper, studies the evolution of ices in the universe at NASA’s Jet Propulsion Laboratory (JPL). Bryana Henderson from JPL and Fred Bateman from the National Institute of Standards and Technology (NIST) also co-authored the paper.

Managing correspondent: Melis Tekant

Original article: Laboratory predictions for the night-side surface ice glow of EuropaNature Astronomy

Media coverage: Europa Glows: Radiation Does a Bright Number on Jupiter’s MoonJet Propulsion Laboratory
Europa’s Mysterious GlowThe Atlantic

Image credit: NASA/JPL

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