Planetary science: Jupiter’s moon Europa may glow in the dark

The night side of Jupiter’s moon Europa may visibly glow, according to laboratory simulations reported this week in Nature Astronomy. NASA’s Europa Clipper mission — set to launch in the mid-2020s —could potentially observe this phenomenon, according to calculations presented in this study.

Europa probably harbours a sub-surface ocean covered by a thick icy crust predominantly made of water ice. The moon’s outer surface is subject to a high level of radiation from Jupiter. Murthy Gudipati and colleagues simulated the interaction of this radiation with Europa’s surface by exposing salted ice to energetic electrons in the laboratory. They found that the irradiated ice emits greenish light in a process called electron-stimulated luminescence. The intensity of the emission depends on the specific composition of the ices.

A low-altitude fly-by from the Europa Clipper spacecraft could determine and map the chemical composition of Europa’s night side surface by measuring how much ice glow is seen at different wavelength regions, argue the authors. Such observations may also allow the characterization of the sub-surface ocean — constraining, for example, its salinity — since the products of ices energetically processed on the surface and ocean materials would be exchanged in geological time scales.