Europa is one of the four major moons of Jupiter, the Galilean satellites. It's covered in a thick crust of ice and has a deep water ocean with possible hydrothermal activity, which means it's considered a possible location for life beyond Earth. Now, a lab experiment suggests it has a weird new property: it might glow green in the dark.
In Nature Astronomy, researchers carried out lab experiments to discern how the ice and salts on the surface of the distant moon may interact with the strong magnetic field of Jupiter. Because the magnetic field accelerates charged particles, Europa is constantly being bombarded by high-energy electrons. These would interact with the chemical substances that make up the exterior of the moon and make it glow.
"We were able to predict that this nightside ice glow could provide additional information on Europa's surface composition," lead author Dr Murthy Gudipati from NASA's Jet Propulsion Laboratory said in a statement. "How that composition varies could give us clues about whether Europa harbors conditions suitable for life."
Lab experiments showed that irradiated ice covered in salt can glow. Very interestingly, the emission is in visible light. The team found that the strongest emission is at 525 nanometers, the wavelength of green light.
But the intensity and the color of the glow depends on the composition of the molecules found in the ice. It's not certain that Europa does glow as these experiments were carried out on Earth, but if it does, this could be used to study what its surface is covered in. For example, common salts such as sodium chloride and carbonate minerals were found to quench the emissions, whereas epsomite instead enhanced it. Knowing this would help us understand if Europa has any of the necessary ingredients for life.
“The work presented here has substantial importance for the characterization of Europa’s surface chemical composition and mineralogy,” the researchers wrote in the paper. “Dark regions could imply sodium- and chloride-dominant surfaces, whereas brighter regions could imply magnesium- and sulfate-dominant surfaces in the absence of water ice.”
The glow cannot be seen by Earth's telescopes, but NASA’s Europa Clipper mission may be able to. The spacecraft is expected to perform repeated close flybys of Europa, and its wide-field camera is expected to be able to pick up the glow of different chemicals when it flies 50 kilometers (31 miles) from its surface in the nighttime. The mission is expected to launch in 2024, and depending on the best trajectory available, it would reach Jupiter between 2027 and 2030.
The focus of this study was specifically on Europa, but it is certainly possible that other bodies in the Solar System – including fellow Galilean moons, Io and Ganymede – may also glow due to intense radiation, which would offer up clues of the composition of their surfaces too.