Europe beckons. A distant ball of ice, one of the 80 known moons of Jupiter, but what's inside matters, and what's inside Europa is predicted to be special.
Beneath Europa's icy surface, scientists predict the existence of a giant hidden ocean: a huge body of water that represents one of the best opportunities to find life in the solar system.
But Europe is not just a 'shining hope' for the discovery of life beyond Earth. According to new studies, the satellite may be bright for another reason – the moon literally glows in the dark.
In the new study, a team led by physicist Murthy Gudipati of California Institute of Technology and NASA's Jet Propulsion Laboratory suggests that radiation from Jupiter's magnetic field could cause a glow on the icy surface that covers Europa, due to reactions with ice chemistry.
“The surface of Europa is constantly experiencing high flows of charged particles due to the presence of Jupiter's strong magnetic field,” the researchers explain in their article.
“Charged high-energy particles, including electrons, interact with a surface rich in ice and salt, leading to complex physical and chemical processes.”
Given that we do not yet fully understand the chemical composition of Europa's ice sheet, it is unclear what these processes will look like, and neither the Keck Observatory in Hawaii nor the Hubble Space Telescope have recorded this hypothetical glow, until now.
However, in the next decade, we will have a better view of Europa's surface when NASA's Europa Clipper spacecraft visits it for the chance to witness a phenomenon called electronically stimulated luminescence.
In the meantime, we can simulate what it might look like by simulating Europa's ice and Jupiter's high-energy electron radiation.
In a series of experiments in the lab, Gudipati's team chilled water ice cores in an aluminum tube to ~ 100 K (-173.15 ° C or -279.67 ° F) and exposed it to pulses of electron radiation.
Visible glow of the irradiated ice core under illumination, darkness and darkness. (Gudipati et al., Nature Astronomy, 2020).
When they did, the ice emitted a glow, but the intensity depended on what chemicals other than ice were present in the water.
“We found that the presence of sodium chloride and carbonate strongly quenched, while epsomite intensified the radiant glow of the ice.”
In addition to proposing the exciting hypothesis that Europa can continuously glow in the dark, even though we are so far away that we cannot detect it, the results could pave the way for new methods of studying the icy moon.
In particular, it is possible that the Europa Clipper imaging systems will be able to observe the glow from orbit (about 50 kilometers above the surface) and, by analyzing the spectra, find out the chemical composition of the ice, distinguishing material from the regions of pure water ice.
In addition to helping with future exploration of Europa, the same methods could lead to new ways of analyzing other moons of Jupiter such as Io and Ganymede.
The results are reported in Nature Astronomy.
