Jupiter’s icy moon Europa is bombarded by a constant and intense blast of radiation from the gas giant. Different salty compounds on the moon’s surface react differently to the radiation and emit their own unique glimmer. 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.
“We were able to predict that this nightside ice glow could provide additional information on Europa’s surface composition,” said lead author Dr. Murthy Gudipati, a researcher at NASA’s Jet Propulsion Laboratory.
“How that composition varies could give us clues about whether Europa harbors conditions suitable for life.”
“That’s because Europa holds a massive, global interior ocean that could percolate to the surface through the moon’s thick crust of ice. By analyzing the surface, we can learn more about what lies beneath.”
The surface of Europa is likely made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate and sodium chloride.
The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow.
“We never imagined that we would see what we ended up seeing,” said co-author Dr. Bryana Henderson, also from NASA’s Jet Propulsion Laboratory.
“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.”
For the study, the researchers built a unique instrument called Ice Chamber for Europa’s High-Energy Electron and Radiation Environment Testing (ICE-HEART).
They took ICE-HEART to a high-energy electron beam facility 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.
They didn’t expect to see variations in the glow itself tied to different ice compositions.
“Seeing the sodium chloride brine with a significantly lower level of glow was the ‘aha’ moment that changed the course of the research,” said co-author Dr. Fred Bateman, a researcher at the National Institute of Standards and Technology.
“A moon that’s visible in a dark sky may not seem unusual; we see our own Moon because it reflects sunlight. But Europa’s glow is caused by an entirely different mechanism,” the scientists said.
“Imagine a moon that glows continuously, even on its nightside — the side facing away from the Sun.”
“If Europa weren’t under this radiation, it would look the way our moon looks to us — dark on the shadowed side,” Dr. Gudipati said.
“But because it’s bombarded by the radiation from Jupiter, it glows in the dark.”
The study appears in the journal Nature Astronomy.
M.S. Gudipati et al. Laboratory predictions for the night-side surface ice glow of Europa. Nat Astron, published online November 9, 2020; doi: 10.1038/s41550-020-01248-1
This article is based on a press-release provided by the National Aeronautics and Space Administration.