Europa's Dark Side Might Glow Colorfully, Revealing Ocean Clues

Lab experiments simulating Europa’s icy surface show that high-energy electrons can energize salts in the ice to emit faint visible light—green, blue, or white—on the moon’s night side. The glow depends on composition and radiation, offering a potential chemical map of surface salts and, indirectly, clues about the subsurface ocean. It’s not a direct ocean readout, and the signal could be faint or variable, but Europa Clipper may test whether such nightside emission exists and helps link surface chemistry to the hidden ocean.