Jupiter’s icy moon Europa glows in the dark

New laboratory experiments recreate the environment of Europa and find that the icy moon shines, even on the night side. The effect is more than a beautiful visual.

As the icy, oceanic moon Europe orbits Jupiter, withstands a relentless blast of radiation. Jupiter hits the surface of Europa night and day with electrons and other particles, immersing it in high-energy radiation. But as these particles hit the moon’s surface, they could also do something otherworldly: make Europa glow in the dark.

New research from scientists a NASAThe Jet Propulsion Laboratory in Southern California describes for the first time what the glow would look like and what it might reveal about the composition of the ice on Europa’s surface. Different saline compounds react differently to radiation and emit their own unique glow. To the naked eye, this glow would sometimes appear slightly green, sometimes slightly blue or white, and with varying degrees of brightness, depending on the material.

Scientists use a spectrometer to separate light into wavelengths and link distinct “signatures”, or spectra, to different ice compositions. Most observations using a spectrometer on a moon like Europa are taken using sunlight reflected on the day side of the moon, but these new results illuminate what Europa would look like in the dark.

“We were able to predict that this nocturnal glare of ice could provide further information on the composition of Europa’s surface. The way this composition varies could give us clues as to whether Europe brings conditions suitable for life, “he said JPLMurthy Gudipati, lead author of the work published November 9 in Nature Astronomy.

This is because Europa has a huge global internal ocean that could seep to the surface through the moon’s thick ice crust. By analyzing the surface, scientists can learn more about what lies beneath.

It shines a light

Scientists have inferred from previous observations that Europa’s surface may be composed of a mixture of ice and salts commonly known on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). The new research shows that incorporating these salts into water ice under conditions similar to those of Europe and detonating it with radiation produces a glow.

That wasn’t a surprise. It is easy to imagine a radiated surface that shines. Scientists know that the shine is caused by energetic electrons penetrating the surface, energizing the underlying molecules. When those molecules relax, they release energy in the form of visible light.

“But we never imagined we would see what we would see,” said Bryana Henderson of JPL, co-author of the research. “When we tried new ice compositions, the glow looked different. And we just stared at it for a while and then we said, ‘This is new, right? Is this definitely a different glow? ‘So we put a spectrometer on it and each type of ice had a different spectrum.’

To study a laboratory model of Europa’s surface, the JPL team built a unique instrument called the Ice Chamber for European High Energy Electron and Radiation Testing (ICE-HEART). They took ICE-HEART to a high-energy electron beam facility in Gaithersburg, Maryland, and began the experiments with an entirely different study in mind: to see how the organic material under Europa Ice would react to the radiation bursts.

They did not expect to see variations in the glow itself related to different ice compositions. It was – as the authors called it – a serendipity.

“Seeing the sodium chloride brine with a significantly lower glow level was the ‘aha’ moment that changed the course of research,” said Fred Bateman, co-author of the article. He helped lead the experiment and delivered radiation beams to ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland.

A moon visible in a dark sky may not seem unusual; we see our Moon because it reflects sunlight. But Europa’s glow is caused by an entirely different mechanism, the scientists said. Imagine a moon that shines continuously, even on the night side, the side facing away from the sun.

“If Europe weren’t under this radiation, it would have the appearance of our moon to us – dark on the shadow side,” Gudipati said. “But since it is bombarded with radiation from Jupiter, it glows in the dark.”

Set for launch in mid-2020, NASA’s next flagship Europa Clipper mission will observe the moon’s surface in multiple close-up passes as it orbits Jupiter. The mission scientists are examining the authors’ findings to assess whether a glow would be detectable by the spacecraft’s science instruments. It is possible that the information gathered by the spacecraft could be matched with measurements from the new research to identify salty components on the lunar surface or narrow down what they might be.

“It’s not often that we are in a laboratory and say, ‘We may find it when we arrive,'” said Gudipati. “It’s usually the other way around: you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that’s what science is about. “

Missions such as Europa Clipper help contribute to the field of astrobiology, interdisciplinary research into the variables and conditions of distant worlds that could host life as we know it. Although Europa Clipper is not a life sensing mission, it will conduct a detailed reconnaissance of Europa and investigate whether the frozen moon, with its subterranean ocean, has the ability to sustain life. Understanding Europa’s habitability will help scientists better understand how life on Earth has developed and the potential to find life beyond our planet.