Future missions could use the eerie glow to map out the complex chemistry of the icy surface and perhaps find clues.
![One of Jupiter's icy moons may glow in the dark](https://technologytimes.pk/wp-content/uploads/2020/11/11-5-785x437.jpg)
BYÂ MAYA WEI-HAAS
If confirmed, future missions could use the eerie glow to map out the complex chemistry of the icy surfaceâand perhaps find clues to whatâs in the ocean below.
JUPITER MIGHT HAVE its own little night light, in the form of an icy moon that glows in the dark.
Like Earthâs lunar companion, the Jovian moon Europa shines brightly on its sunlight side. But our rocky lunar neighbor is swathed in darkness on its far side, which is part of why we see the moon wax and wane and even seem to vanish from sight. Now, laboratory experiments suggest that ice on the far side of Europa might instead give off a visible greenish or bluish white light, driven by the constant bombardment of radiation from Jupiterâs intense magnetic field.
âIt would be a nice fairytale-like thing to stand on Europa and see,â says Murthy Gudipati, an astrophysicist at NASAâs Jet Propulsion Laboratory and lead author of the new study, published today in Nature Astronomy.
The team tested ice laced with a variety of different salts thought to linger on Europaâs surface, discovering that the precise composition influences the intensities of colors that make up the glow. That means if Europaâs surface does glow, future missions could study the light from the moonâs nighttime side to help decipher its complex chemistry. That in turn could provide clues to the composition of the deepâand potentially habitableâocean thought to exist below Europaâs icy crust.
In the next few years, two ventures will start the lengthy trip to get a closer look: NASAâs Europa Clipper and the European Space Agency’s Jupiter Icy Moons Explorer (JUICE). This new study adds âanother tool in our toolboxâ to help future scientists work out Europaâs complex surface chemistry, says Curt Niebur, the Europa Clipper Program Scientist with NASA, who was not part of the study team.
âBut also,â he says, âif the surface glows, thatâs just cool.”
Scientists have known since the 1950s that pure water ice glows when exposed to radiation, says Anna Pollmann, an astroparticle physicist at the University of Wuppertal. When electrons collide with molecules in the ice, they impart a small amount of energy. These âexcitedâ molecules canât stay that way for long, quickly releasing the energy in the form of light.
Pollmann, who was a reviewer of the new study, uses these faint winks of light in Antarctic ice to search for exotic cosmic particles thought to rain down on our planet. But Earthâs thick atmosphere and magnetic bubble shield our planet from much incoming radiation, making these streaks of luminescence scarce.
By contrast, Europa has almost no atmosphere and is caught up in the maelstrom of radiation from Jupiterâs fierce and enormous magnetic field. Thereâs so much radiation scouring the moonâs surface that if you stood on Europa unprotected, you would die within 10 to 20 minutes, Niebur says.
Gudipati and his colleagues initially had planned to study how this radiation might affect the properties of Europaâs icy crust, which is critical to understand if we ever send landers to the alien moon. They built an instrument that allowed them to bombard chunks of ice with a stream of electrons and track what happens from a safe distance. Gudipati dubbed the setup ICE-HEART, or Ice Chamber for Europa High-Energy Electron and Radiation-Environment Testing.
When they shone the electron beam onto a frozen block of pure water, the icy glow caught their attention. Then, they switched to sodium chloride ice, and the light was very faint. Thinking something was wrong, Gudipati and his colleagues tried it againâstill no glow.
âThat was the ah-ha moment for us,â Gudipati says.
He and his team tested a variety of salts that studies have hinted could linger on Europaâs surface. Some salts, like carbonates, seem to quench the glow. But others, like magnesium salts, give it a boost. The intensities of the colors that make up the glow also changed. For example, sodium chloride staunches green light, while sulfate salts add slightly more red to the mix.
The results suggest that the presence of different salts will influence any potential gleam coming from the ice moonâs surfaceâa feature that could perhaps âhelp us look at Europa through different eyes,â he says.
Gudipati and his teamâs calculations suggest that the moon’s radiation likely generates enough ice glow to be seen by the Europa Clipperâs camera. That doesnât mean itâs a surefire thing, Niebur cautionsââthat camera is still being built.â
âThereâs a lotâa lotâwe still need to learn about the moon,â Belgacem says.
A spacecraft hasn’t studied Europa in detail since the Galileo mission in the 1990s, making it difficult to fill in our knowledge of this icy world. But answers might be coming soon from Clipper and JUICE, and the new study only adds to that potential.
âThe more we know before we get there,” she says, “the better it will be for the science we can get.”
Originally published at nationalgeography