Jupiter's icy, oceanic moon must shine in the dark

Katie Ramirez
November 12, 2020

Giving a new meaning to the word "moonshine", NASA scientists at the Jet Propulsion Laboratory (JPL) in Pasadena, California, have concluded that Jupiter's moon Europa glows in the dark due to being constantly bombarded with high-energy radiation.

If you managed to make it to Jupiter and then looked at the dark side of its moon Europa, you might be blown away by an ethereal glimmer.

As well as seeing evidence of key chemical and physical changes in Europa's crust, Jupiter's radiation breaks water ice into oxygen and hydrogen, boosting the chances that oxygen filters down to the liquid ocean below - the researchers observed the ice visibly glowed.

"We were able to predict that this nightside ice glow could provide additional information on Europa's surface composition".

This nightside glow - it won't be visible on Europa's sun-illuminated dayside - has more than just gee-whiz appeal.

"Owing to the unique radiation environment and rich geological and compositional diversity on its surface, the night-time ice glow occurring on Europa may be very unique and unlike any other phenomenon in our Solar System", the authors write in their paper.

A moon that "glows" in the night sky doesn't exactly sound that remarkable because our moon continues reflecting the sun's light at night time, so we're used to the sight, but the underlying mechanism behind Europa's glow is much different, as even its dark side which faces away from the sun emits light. With this help, radiation will be studied on the surface of Europa.

The intensity of the glow depends on the composition of the ice: the presence of sodium chloride and carbonate produced a fainter light, while epsomite produced a brighter light. The fascinating icy moon may sport a glow-in-the-dark nightside triggered by blasting radiation.

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"The spectrum of the glow would give more clues about the subsurface ocean", he said in an email.

"But we never imagined that we would see what we ended up seeing", said JPL's Bryana Henderson, who co-authored the research.

They didn't expect to see variations in the glow itself tied to different ice compositions.

"Radiation is indeed a form of energy, like sunlight reaching Earth - that is critical for life on Earth", Murthy said. He helped conduct the experiment and delivered radiation beams to the ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland. In fact, mission scientists have already begun examining the findings of the study in order to analyze if such a glow could be detected on the moon using the scientific instruments that the spacecraft will be equipped with.

"It's not often that you're in a lab and say, 'We might find this when we get there".

"Understanding its chemistry, the composition of the ocean, is an important piece of the puzzle to understanding whether Europa could be a habitable environment", Bob Pappalardo, Europa mission project scientist at JPL, said. It's possible that information gathered by the spacecraft could be matched with the measurements in the new research to identify the salty components on the moon's surface or narrow down what they might be. "Usually it's the other way around - you go there and find something and try to explain it in the lab". "We don't know a lot about Europa now, and with the Europa Clipper mission that will be going, we want to much better understand the big picture of what makes Europa work". "But our prediction goes back to a simple observation, and that's what science is about".

Europa Clipper is set to launch in the mid-2020s and it's set to be one of the most exciting missions of the decade as it will investigate a part of the solar system that's promising in regards to extraterrestrial life.

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