Cosmic radiation may have created some of the organic molecules found on the icy moon

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This article was originally published Eos. The publication contributed to the article on Space.com Expert Voices: Op-Ed & Insights.

New laboratory studies show that some organic molecules has previously been discovered in the plumes erupting from Saturn’s moons Enceladus may be products of natural radiation rather than originating from the Moon’s subsurface ocean. This finding complicates the evaluation of the astrobiological importance of these compounds.

Enceladus hides a global ocean buried under a frozen crust. Material from this fluid reservoir is ejected into space from ice fissures near the South Pole, forming plumes of dust-sized ice particles that stretch for hundreds of kilometers. Although most of this material falls to the surface, some remains in orbit and becomes part of it Saturn’s E ringthe outermost and widest ring of the planet.

2005-2015 NASA The Cassini spacecraft has flown past these columns many times and found various organic molecules. The discovery was seen as evidence of a chemically rich and potentially habitable environment beneath the ice molecules necessary for life could be available. But the new study offers an explanation that radiation, not biology, is behind the presence of at least some of these organic molecules.

To test the role of cosmic radiation, a team of researchers led by a planetary scientist Grace RichardsPhD student at the National Institute of Astrophysics in Rome, simulated conditions near the surface of Enceladus by creating a mixture of water, carbon dioxide, methane and ammonia, which are the main likely components of surface ice on Enceladus’ surface. They cooled the mixture to -200°C in a vacuum chamber and then bombarded it with water ions, which are an important component of the radiation environment surrounding the Moon.

The radiation caused a series of chemical reactions that produced a cocktail of molecules, including carbon monoxide, cyanate, ammonium, and various alcohols, as well as the molecular precursors of amino acids such as formamide, acetylene, and acetaldehyde. The presence of these simple molecules suggests that radiation can cause similar reactions on Enceladus.

Richards presented these findings at a joint meeting of the Europlanet Science Congress and Division of Planetary Sciences (EPSC-DPS 2025) in Helsinki, Finland. She and her co-authors also published a detailed report Planetary and space science.

Enceladus and beyond

The new study raises the question of whether organic molecules have been detected Enceladus plumes certainly come from the Moon’s buried ocean, whether they formed in space or form near the surface as plumes leave Enceladus’ interior.

While this finding does not rule out the possibility that Enceladus may have a habitable ocean, Richards urges caution in making assumptions about the presence of these molecules in the plumes, their origin, and their possible role as precursors to biochemistry.

“I don’t necessarily think my experiments discredit anything to do with the habitability of Enceladus,” Richards said.

But she added, “When you’re trying to infer this ocean composition from what you see in space, it’s important to understand all the processes that are going on to change this material.” In addition to radiation, these processes include phase changes, interactions with lunar ice walls, and interactions with the space environment.

“We need a lot of these types of experiments,” said the planetary scientist Alex’s bouquetA researcher at the French National Center for Scientific Research (CNRS) at L’Université d’Aix-Marseille, who was not involved in the study. “They showed that you can grow a certain diversity of species under conditions that are important for Enceladus’ south pole.”

Bouquet emphasized the importance of simulating these environments in the laboratory for planning future missions to Enceladus and for interpreting the highly anticipated current data. missions to the icy moons of Jupiter. These missions are NASA Europa Clipper.which will explore Europe and European Space Agency‘s (ESA) JUICE (Jupiter Icy Moons Explorer), which will visit all three moons of the giant planet with underground oceans: Ganymede, Callisto, and also Europe.

The intense radiation around Jupiter makes these experiments particularly important. “Radiation chemistry of Europa’s or Jovian moons in general.” [is] a big deal, a bigger deal than Enceladus,” says Bouquet.

It’s a completely different story

As Richards’ work raises the question of the origin of the organic compounds around Enceladus, scientists are adding more molecules to the puzzle.

After a new data collected during one of the Cassiniin 2008 researchers led by a planetary scientist close to Enceladus Nozair Khawaja Freie Universität Berlin and the University of Stuttgart have reported the discovery of new types of organic molecules that appear to emerge from icy vents. They include ester and ether groups and chains and cyclic species with oxygen and nitrogen double bonds.

On Earth, these molecules are essential links in the chemical reactions that ultimately create the complex compounds necessary for life. And while these molecules may be of inorganic origin, “they increase the habitability of Enceladus.”
Khawaja said. The findings appeared in Natural astronomy.

Khawaja’s team’s analysis shows that complex organic molecules are present in fresh ice grains just thrown from the vents. During its last flyby, Cassini came as close as 28 kilometers to the Moon’s surface.

After modeling the plumes and the residence time of the ice grains in space, they believe that the ice grains picked up by Cassini did not spend much time in space, likely only “a few minutes,” Khawaja said. “It’s fresh.”

This short duration in space raises the question of whether cosmic radiation had enough time to create the organic molecules Khawaja discovered. Just a few minutes would not be enough for such complex chemistry to occur, even in a high-radiation environment.

“Large grains coming from the surface, full of organic matter? That’s much harder to explain with radiation chemistry,” Bouquet said.

While the types of experiments Richards performed “are valuable and take science to the next level,” Khawaja said, “our results tell a completely different story.”

Back to Enceladus

Both studies reinforce the complexity of Enceladus’ chemistry, making it a prime target for the search for extraterrestrial life, or at least the building blocks of life. Enceladus has all three necessary conditions for life: liquid water, a source of energy and a rich cocktail of chemical elements and molecules. Even if the subsurface ocean is inaccessible—it’s at least several kilometers beneath the ice near the poles—the plumes provide the only known opportunity to sample an extraterrestrial liquid ocean.

Research into a potential ESA mission to Enceladus is already underway, with plans for fast pole flights and possibly a lander at the south pole. Insights from both recent studies will help scientists design devices and guide the interpretation of future results.

“There is no better place to look [life] than Enceladus,” Khawaja said.