Jupiter’s icy moon Europa could give the word “moonlight” a whole new meaning. New lab experiments suggest the nightside of this moon glows in the dark.
Europa’s surface, thought to be mostly water ice laced with various salts, is continually bombarded with energetic electrons by Jupiter’s intense magnetic field (SN: 5/19/15). When researchers simulated that interaction in the lab by shooting electrons at salty ice samples, the ice glowed. The brightness of that glow depended on the kind of salt in the ice, researchers report online November 9 in Nature Astronomy.
If the same interaction on Europa creates this never-before-seen kind of moonlight, a future mission there, such as NASA’s planned Europa Clipper spacecraft, may be able to use this ice glow map Europa’s surface composition. That, in turn, could give insight into the salinity of the ocean thought to lurk under Europa’s icy crust (SN: 6/14/19).
“That has implications for the temperature of that liquid water — the freezing point; it has implications for the thickness of the ice shell; it has implications for the habitability of that liquid water,” says Jennifer Hanley, a planetary scientist at Lowell Observatory in Flagstaff, Ariz. not involved in the new work. Europa’s subsurface ocean is considered one of the most promising places to look for extraterrestrial life in the solar system (SN: 4/8/20).

Sign Up For the Latest from Science News

Headlines and summaries of the latest Science News articles, delivered to your inbox

The discovery of Europa’s potential ice glow “was serendipity,” says Murthy Gudipati, who studies the physics and chemistry of ices at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Gudipati and colleagues originally set out to investigate how electron bombardment might change the chemistry of Europa’s surface ice. But in video footage of their initial experiments, the team noticed that ice samples pelted with electrons gave off an unexpected glow.
Intrigued, the researchers turned their electron beam on samples of pure water ice, as well as water ice mixed with different salts. Each ice core was cooled to the surface temperature of Europa (about –173° Celsius) and showered with electrons that had the same energies as those that strike Europa. Over 20 seconds of irradiation, a spectrometer measured the wavelengths of light, or spectrum, given off by the ice.
The ice samples all gave off a whitish glow, because they emitted light at many different wavelengths. But the brightness of each ice sample depended on its composition. Ice containing sodium chloride, also known as table salt, or sodium carbonate appeared dimmer than pure water ice. Ice mixed with magnesium sulfate, on the other hand, was brighter.

“I was doing some back of the envelope calculations [of] what would be the brightness of Europa, if we were to be standing on it in the dark,” Gudipati says. “It’s approximately … as bright as me walking on the beach in full moonlight.”
Based on the specs proposed for a camera to fly on the Europa Clipper mission, Gudipati and colleagues estimate that the spacecraft could see Europa’s ice glow during a flyby of the dark side of the moon. Dark patches of Europa could reveal sodium-rich regions, while brighter areas may be rich in magnesium.
But seeing ice glow in the lab does not necessarily mean it happens the same way on Europa, Hanley cautions. Jupiter’s icy moon has been barraged by high-energy electrons for a lot longer than 20 seconds. “Is there ever a point where you might break down the salts, and this glow stops happening?” she wonders.
Other planetary scientists, meanwhile, are not convinced that Europa’s surface is highly salted. These researchers, including Roger Clark of the Planetary Science Institute in Lakewood, Colo., think the apparent hints of salts on Europa are actually created by acids, such as sulfuric acid. Europa’s surface may be coated in both salts and acids, Clark says. “What [the researchers] need to do next is irradiate acids … to see if they can tell the difference between salt with water ice and acids with water ice.” More

Rivers may have operated on a global scale around 3.5 billion years ago.

The new find comes courtesy of ancient rocks in China and South Africa. A change in rock chemistry around that time provides the earliest known chemical evidence for the weathering of Earth’s continents and the subsequent delivery of nutrients from land to ocean, geobiologist Kurt Konhauser and colleagues report December 12 in Geology.

Water chips away at rocks on land, removing minerals and washing them away. “As soon as you get weathering, you’ve got a nutrient influx to the oceans, which can lead to … life thriving in coastal waters,” says Konhauser, of the University of Alberta in Edmonton, Canada. More

A surprisingly short gamma-ray burst has astronomers rethinking what triggers these celestial cataclysms.

The Fermi Gamma-ray Space Telescope detected a single-second-long blast of gamma rays, dubbed GRB 200826A, in August 2020. Such fleeting gamma-ray bursts, or GRBs, are usually thought to originate from neutron star smashups (SN: 10/16/17). But a closer look at the burst revealed that it came from the implosion of a massive star’s core.

In this scenario, the core of a star collapses into a compact object, such as a black hole, that powers high-speed particle jets. Those jets punch through the rest of the star and radiate powerful gamma rays before the outer layers of the star explode in a supernova (SN: 5/8/19). That process is typically thought to produce longer GRBs, lasting more than two seconds.

Discovering such a brief gamma-ray burst from a stellar explosion suggests that some bursts previously classified as stellar mergers may actually be from the deaths of massive stars, researchers report online July 26 in two studies in Nature Astronomy.

The first clues about GRB 200826A’s origin came from the burst itself. The wavelengths of light and amount of energy released in the burst were more similar to collapse-related GRBs than collision-produced bursts, Bing Zhang, an astrophysicist at the University of Nevada, Las Vegas, and colleagues report. Plus, the burst hailed from the middle of a star-forming galaxy, where astronomers expect to find collapsing massive stars, but not neutron star mergers — which are generally found on the fringes of tranquil galaxies.

Another group, led by astronomer Tomás Ahumada-Mena of the University of Maryland in College Park, searched for the supernova that’s expected to follow a GRB produced by a collapsing star. Using the Gemini North Telescope in Hawaii to observe GRB 200826A’s host galaxy, the team was able to pick out the telltale infrared light of the supernova. The burst may have been so brief because its jets had just barely punched through the surface of the star before they petered out and the star blew up, Ahumada-Mena says. More

A suspected subsurface ocean on Pluto might be old and deep. New analyses of images from NASA’s New Horizons spacecraft suggest that the dwarf planet has had an underground ocean since shortly after Pluto formed 4.5 billion years ago, and that the ocean may surround and interact with the rocky core. If so, oceans could […] More

In a galaxy not so far away, astronomers have located a surprising source of a mysterious, rapid radio signal.

The signal, a repeating fast radio burst, or FRB, was observed over several months in 2021, allowing astronomers to pinpoint its location to a globular cluster — a tight, spherical cluster of stars — in M81, a massive spiral galaxy 12 million light-years away. The findings, published February 23 in Nature, are challenging astronomers’ assumptions of what objects create FRBs.

“This is a very revolutionary discovery,” says Bing Zhang, an astronomer at the University of Nevada, Las Vegas who was not involved in the study. “It is exciting to see an FRB from a globular cluster. That is not the favorited place people imagined.”

Sign Up For the Latest from Science News

Headlines and summaries of the latest Science News articles, delivered to your inbox

Thank you for signing up!

There was a problem signing you up.

Astronomers have been puzzling over these mysterious cosmic radio signals, which typically last less than a millisecond, since their discovery in 2007 (SN: 7/25/14). But in 2020, an FRB was seen in our own galaxy, helping scientists determine one source must be magnetars — young, highly magnetized neutron stars with magnetic fields a trillion times as strong as Earth’s (SN: 6/4/20).

The new findings come as a surprise because globular clusters harbor only old stars — some of the oldest in the universe. Magnetars, on the other hand, are young leftover dense cores typically created from the death of short-lived massive stars. The magnetized cores are thought to lose the energy needed to produce FRBs after about 10,000 years. Globular clusters, whose stars average many billions of years old, are much too elderly to have had a sufficiently recent young stellar death to create this type of magnetar. 

To pinpoint the FRB, astronomer Franz Kirsten and colleagues used a web of 11 radio telescopes spread across Europe and Asia to catch five bursts from the same source. Combining the radio observations, the astronomers were able to zero in on the signal’s origins, finding it was almost certainly from within a globular cluster.

“This is a very exciting discovery because it was completely unexpected,” says Kirsten, of ASTRON, the Netherlands Institute for Radio Astronomy, who is based at the Onsala Space Observatory in Sweden.

The new FRB might still be caused by a magnetar, the team proposes, but one that formed in a different way, such as from old stars common in globular clusters. For example, this magnetar could have been created from a remnant stellar core known as a white dwarf that had gathered too much material from a companion star, causing it to collapse.

“This is a [magnetar] formation channel that has been predicted, but it’s hard to see,” Kirsten says. “Nobody has actually seen such an event.”

Alternatively, the magnetar could have been formed from the merger of two stars — such as a pair of white dwarfs, a pair of neutron stars or one of each — in close orbit around one another, but this scenario is less likely, Kirsten says. It’s also possible the FRB source isn’t a magnetar at all but a very energetic millisecond pulsar, which is also a type of neutron star that could be found in a globular cluster, but one that has a weaker magnetic field.

To date, only a few FRB sources have been precisely pinpointed, and their locations are all in or close to star-forming regions in galaxies. Besides adding a new source for FRBs, the findings suggest that magnetars created from something other than the death of young stars might be more common than expected. More