Jupiter’s Europa moon glows as it gets bombarded by radiation from the gas giant. The glow could tell scientists a lot about Europa’s surface composition.
The icy, ocean-filled moon is a cosmic beacon. It glows as it orbits Jupiter in the deep darkness far from the sun.
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The reason why our moon shines in the sky is that it reflects light from the Sun. Jupiter and its moons are about five times farther away from the Sun than the Earth is. But the Sun still illuminates them.
However, Europa moon glows even in the night side, shadowed by Jupiter.
The moon produces an ethereal glimmer without the help of the sun and that’s due to high-energy radiation from Jupiter.
The gas giant zaps Europa’s surface night and day with electrons and other particles. These charged particles zoom around Jupiter at tremendous speeds, trapped and accelerated by the giant planet’s powerful magnetic field. As they hit Europa’s surface, they could make it glow.
In order to better understand this process a JPL research team created a laboratory mock-up of Europa’s surface in a high-energy electron beam facility in Gaithersburg, Maryland, and subjected it to an instrument called Ice Chamber for Europa’s High-Energy Electron and Radiation Environment Testing (ICE-HEART).
They tested the effects of radiation on simulated Europa surfaces composed of water ice and various salts suspected to be there, including sodium chloride and magnesium sulfate. The radiation caused the samples to glow.
This, however, was a well-known phenomenon for scientists. Fast-moving particles penetrated into the sample, exciting molecules in the near subsurface and generating a glow.
“But we never imagined that we would see what we ended up seeing,” study co-author Bryana Henderson, also of JPL, said in the same statement. “When we tried new ice compositions, the glow looked different. And we all just stared at it for a while and then said, ‘This is new, right? This is definitely a different glow?’ So we pointed a spectrometer at it, and each type of ice had a different spectrum.”
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The glow varied with the composition of the ice. This suggests that the “dark” side of Europa actually has a glow of varying hue and brightness that is sometimes slightly green, blue, or white.
The fact that the glow changed with the material was a pleasant surprise because it gives scientists another tool for learning more about the interior of Europa. And, because water from Europa’s buried ocean probably makes its way to the moon’s surface in places, “how that composition varies could give us clues about whether Europa harbors conditions suitable for life,” study lead author Murthy Gudipati, a scientist at NASA’s Jet Propulsion Laboratory (JPL) said.
Scientists use a spectrometer to separate the light into wavelengths and connect the distinct “signatures,” or spectra, to different compositions of ice. Most observations using a spectrometer on a moon-like Europa are taken using reflected sunlight on the moon’s dayside, but these new results illuminate what Europa would look like in the dark.
Scientists will get a chance to look for the real thing in this decade. NASA is currently developing a robotic mission to Europa, named Clipper, set to launch in the mid-2020s. The probe will observe the moon’s surface in multiple flybys while orbiting Jupiter. Mission scientists are reviewing the authors’ findings to evaluate if a glow would be detectable by the spacecraft’s science instruments.
The Clipper mission will gather data that will help researchers assess the moon’s habitability and plan out a life-hunting Europa lander mission.
“It’s not often that you’re in a lab and say, ‘We might find this when we get there,'” Gudipati said. “Usually it’s 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.”