The possibility that Enceladus, a moon of Saturn, could harbor life has resurfaced. New organic molecules linked to life have been discovered on this body. Twenty years ago, organics were observed in plumes erupting from its subsurface, making Enceladus known as the most likely body in the solar system after Earth to host life.
Recently, some argued that organics found on Enceladus were formed on the surface by cosmic radiation, not in the subsurface ocean, raising skepticism about life. With the new discovery of complex organic molecules closely related to life, hope has revived that life might be found beyond Earth. Scientists said it is still hard to draw conclusions, so it is worth continuing exploration.
◇ Verifying interior material of the moon from Saturn orbit
The European Space Agency (ESA) said on the 1st in the journal Nature Astronomy that "an analysis of data observed by the Cassini probe while orbiting Saturn found that new complex organic molecules are being emitted from Enceladus."
The Cassini team explained that the emergence of new organic molecules is clear evidence that complex chemical reactions are occurring in Enceladus' subsurface ocean. They suggested that some of these reactions could be parts of chain reactions leading to molecules associated with life.
According to a March announcement by the International Astronomical Union (IAU), Saturn has 274 moons. Enceladus is the sixth-largest among them and has been cited as a body with an ocean that could harbor extraterrestrial life. In 2005, Cassini observed plumes erupting from so-called "tiger stripes," cracks in the surface at Enceladus' south pole.
A team led by Professor Nozair Khawaja of Freie Universität Berlin analyzed data observed by Cassini until it completed its mission in 2017. Each time Cassini passed through Saturn's E ring, it continued to detect ice particles originating from Enceladus. Scientists found many organic molecules in these ice particles. They also contained precursors that could become amino acids that build proteins in life.
The problem is that the ice particles in Saturn's rings may have been exposed to cosmic radiation for centuries, potentially altering their chemical properties. To find answers, the team examined fresher ice particles emitted more recently. In 2008, Cassini flew straight through the ice ejecta of Enceladus. Fresh particles emitted just minutes earlier struck Cassini's Cosmic Dust Analyzer (CDA) at about 18 km per hour.
Khawaja said "speed" was the key to this study. Ice particles emitted from Enceladus also contain other molecules such as organics, and if Cassini collides slowly, the ice shatters and clusters of water molecules form, masking signals from other molecules. By contrast, if ice particles strike the analyzer quickly, signals from organic molecules can be captured before water emerges.
After years of analyzing Cassini data, the team confirmed that organic molecules found in Saturn's E ring were also present in ice grains that came from Enceladus. This demonstrated that the organic molecules did not arise from cosmic radiation but came from Enceladus' subsurface ocean.
◇ Green light for additional Enceladus exploration
In particular, the analysis found more complex organic molecules not detected before. The team said, "This discovery is not evidence that life exists on Enceladus, but it suggests that complex chemical pathways capable of leading to the formation of biologically relevant substances are at work," adding that it "supports ESA's plans to search for signs of life." The researcher added, "All signals for Enceladus appear green (go)."
Based on magnetic and gravitational observations, scientists estimated that Enceladus has an ocean beneath the surface at a depth of about 40 km, with a maximum depth of 10 km. In other words, an ocean lies between the surface ice layer and the rocky core. Enceladus' subsurface ocean is heated by tidal forces from Saturn and vents plumes to the surface. The James Webb Space Telescope captured this phenomenon in 2023. At that time, the plume extended nearly 10,000 km. Some was pulled by Saturn's gravity into the rings.
No probe has yet directly explored Enceladus' subsurface ocean. Only indirect evidence has been found. That limitation is why skepticism about life persists. Last month, scientists at the National Institute for Astrophysics (INAF) in Italy argued in the journal Planetary and Space Science that organic molecules observed in Enceladus' plumes may have been generated on the surface by cosmic radiation, not in the subsurface ocean. In experiments simulating Enceladus' environment, the team produced precursor molecules to amino acids using radiation.
This study confirmed for now that the organics in Saturn's rings came from Enceladus' plumes and were present in the plumes from the moment of emission, not formed after long exposure to cosmic radiation. It does not yet refute the Italian team's experiments, but it kept the debate from tipping to one side.
Scientists are hoping for a new direct exploration of Enceladus to follow Cassini. Jörn Helbert, head of ESA's solar system program, who did not take part in this study, said in an interview with the Guardian in the United Kingdom that "a new mission planned for launch around 2042 will consist of an orbiter that will circle Enceladus and pass through the plumes, and a lander that will touch down in the south polar region of Enceladus," adding that "since Enceladus has all the elements to harbor life—liquid water, energy, and complex organic molecules—it is timely to send a probe to search for its traces."
References
Nature Astronomy (2025), DOI: https://doi.org/10.1038/s41550-025-02655-y
Planetary and Space Science (2025), DOI: https://doi.org/10.1016/j.pss.2025.106179