Europa glowing
An illustration shows how Europa might glow on the night side that faces away from the sun.
  • Jupiter's oceanic moon, Europa, might glow white, blue, and green in the dark, a NASA scientist discovered.
  • Jupiter bombards Europa's icy surface with high-energy electrons that makes some types of ice glow.
  • Mapping Europa's "mosaic" of nighttime glow could narrow down the chemical ingredients of the ice.
  • NASA plans to send a spacecraft to Europa, where it could scan for the glow and for chemical ingredients of life.
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One of the solar system's best candidates for alien life — an ocean world calledEuropa — might glow in the dark.

Europa is a moon of Jupiter that hides a global ocean deep beneath its icy crust. But the moon's surface is constantly bombarded with radiation from Jupiter, which could be making its ice glow white, green, or even blue, according to a study published Monday in the journal Nature Astronomy.

As a result, strolling across Europa's surface would be like taking "a walk on the beach in full moonlight," Murthy Gudipati, a NASA planetary scientist who led the new research, told Business Insider.

Gudipati's team wanted to find out how far Jupiter's high-energy electrons could penetrate into Europa's icy surface, and whether they would cause any chemical reactions.

To simulate the conditions on the oceanic moon, the researchers blasted water ice in a laboratory with Jupiter-like radiation. They noticed the ice was glowing brilliantly — no surprise, since past studies have found that bombarding pure ice with electrons can give it an irradiated light. But when they did the same to a frozen table-salt brine, the glow virtually disappeared.

"We thought, 'Oh there was something wrong, the electrons were not coming through,' and we checked everything," Gudipati said. "Everything was fine. We went back to [pure] water ice and it was glowing."

He added, "Our aha moment was that, huh, this looks like this glow is actually depending upon what kind of composition this ice has."

An artist's concept of the ocean below Europa's surface and its intrusions into the ice above.

So the researchers pivoted to experiment with different chemical compositions. Sodium sulfate water? Glowing. Sodium carbonate water? Dull.

Scientists haven't yet determined the precise composition of Europa's surface ice, but they think it's filled with sulfates and sulfuric acid, based on data from NASA spacecraft and telescopes. This research suggests those compounds should glow as Jupiter blasts them with electrons.

Europa's surface also seems to have frozen table-salt brines, which would appear more dull.

"I think that we have a mosaic patch of different compositions on the surface. That would lead it to glow in some parts much more, some parts less, some parts no glow, so it looks really like a mosaic," Gudipati said. "The exciting thing is to go and see how it would be."

The thin, icy crust of Europa, blanketed in ice particles from a crater 620 miles away.

Studying Europa's glow could therefore tell scientists a lot about the chemical makeup of the ice and the ocean deep beneath it. Bright luminescent areas would likely be either pure water ice or ice containing sulfates or magnesium. Darker regions could be ice with more salt or carbonates — compounds that don't emit light in response to Jupiter's radiation.

Patches of ice that glow differently than their surroundings could be areas where ocean water once burst through, then settled and froze on the surface. Mapping all these different gleaming patches could tell scientists a lot about Europa's potential to host life.

NASA is sending a probe to Europa

The reason Europa can keep water in a liquid state is that it follows an oval-shaped orbit around Jupiter. The giant planet's gravity stretches and relaxes the moon, and that friction warms Europa's deep underground salt water, keeping it liquid. The process could even allow the moon to harbour deep-sea ecosystems.

An artist's rendering of NASA's Europa Clipper spacecraft.

NASA plans to send a spacecraft, the Europa Clipper, to the Jovian moon. The probe could send back images of Europa's dark side. The mission plan calls for it to fly by the oceanic moon 45 times, getting as close as 25km above its surface.

Such close range could enable the Clipper to fly through plumes of water vapour that shoot through Europa's ice, since those are known to crest more than 160km above the surface. This water seems to come from the ocean below, and it could contain signs of life.

An illustration of salty ocean water spraying from the icy crust of Europa.

Sampling the water could tell scientists whether Europa's oceans have the chemical ingredients for life: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

The Europa Clipper is set to launch as early as 2024.

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