But Europa's glow is caused by an entirely different mechanism, the scientists 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.Ī moon that's visible in a dark sky may not seem unusual we see our own Moon because it reflects sunlight. "Seeing the sodium chloride brine with a significantly lower level of glow was the 'aha' moment that changed the course of the research," said Fred Bateman, co-author of the paper. It was-as the authors called it-serendipity. They didn't expect to see variations in the glow itself tied to different ice compositions. They took ICE-HEART to a high-energy electron beam facility in Gaithersburg, Maryland, and started the experiments with an entirely different study in mind: to see how organic material under Europa ice would react to blasts of radiation.
To study a laboratory mockup of Europa's surface, the JPL team built a unique instrument called Ice Chamber for Europa's High-Energy Electron and Radiation Environment Testing (ICE-HEART). 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." "When we tried new ice compositions, the glow looked different. "But we never imagined that we would see what we ended up seeing," said JPL's Bryana Henderson, who co-authored the research. When those molecules relax, they release energy as visible light. Scientists know the shine is caused by energetic electrons penetrating the surface, energizing the molecules underneath. It's easy to imagine an irradiated surface glowing. The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow. Scientists have inferred from prior observations that Europa's surface could be made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). By analyzing the surface, scientists can learn more about what lies beneath. That's because Europa holds a massive, global interior ocean that could percolate to the surface through the moon's thick crust of ice. How that composition varies could give us clues about whether Europa harbors conditions suitable for life," said JPL's Murthy Gudipati, lead author of the work published Nov. "We were able to predict that this nightside ice glow could provide additional information on Europa's surface composition. 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 use a spectrometer to separate the light into wavelengths and connect the distinct "signatures," or spectra, to different compositions of ice. To the naked eye, this glow would look sometimes slightly green, sometimes slightly blue or white and with varying degrees of brightness, depending on what material it is. Different salty compounds react differently to the radiation and emit their own unique glimmer. New research from scientists at NASA's Jet Propulsion Laboratory in Southern California details for the first time what the glow would look like, and what it could reveal about the composition of ice on Europa's surface.
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