Saturn's moon Enceladus is constantly spewing out a plume of icy grains and gases coming from its underground ocean through cracks near its south pole. Using data from NASA's Cassini spacecraft, a team of planetary scientists from the University of Stuttgart and the Free University of Berlin conducted a chemical analysis of freshly ejected particles originating directly from Enceladus's ocean. They were able to detect intermediate compounds of potentially biologically significant organic molecules – aliphatics, (hetero)cyclic esters/alkenes, ethers/ethyls, and presumably nitrogen- and oxygen-containing compounds – which were thus discovered for the first time in ice particles from oceans beyond Earth.
An artist's impression of NASA's Cassini spacecraft flying through plumes bursting from Enceladus's south pole; These plumes are very similar to geysers and emit a mixture of water vapor, ice grains, salts, methane and other organic molecules. Image credit: NASA/JPL-Caltech.
Enceladus has a diameter of about 500 km; its surface is covered with an ice shell with an average thickness of approximately 25-30 km.
In 2005, Cassini found the first evidence that there is a hidden ocean beneath the surface of Enceladus.
Jets of water erupted from cracks near the moon's south pole, spewing ice grains into space.
Some of the tiny pieces of ice, smaller than grains of sand, fall back onto the moon's surface, while others escape and form a ring around Saturn that follows the orbit of Enceladus.
“Cassini kept detecting samples from Enceladus as it flew through Saturn's E ring,” said Free University of Berlin researcher Nozair Khawaja, lead author of the study.
“In these ice grains, we have already discovered a variety of organic molecules, including amino acid precursors.”
The ice grains in the ring may be hundreds of years old. As they age, they may have been “weathered” and therefore changed by intense cosmic radiation.
Scientists wanted to study fresh grains that were ejected more recently to better understand what exactly was happening in Enceladus's ocean.
Luckily, they already had the data. Back in 2008, Cassini flew straight through the icy spray. Untouched grains ejected just minutes before hitting the spacecraft's Cosmic Dust Analyzer (CDA) at a speed of about 18 km/s. Not only were these the freshest ice grains Cassini had ever detected, but they were also the fastest.
“Ice grains contain not only frozen water, but also other molecules, including organic matter,” Dr. Khawaja said.
“At lower impact velocities, the ice breaks up and the signal from clusters of water molecules can obscure the signal from certain organic molecules.”
“But when the ice grains quickly reach the CDA, the water molecules don't cluster and we have a chance to see these previously hidden signals.”
It took years to accumulate knowledge from previous flybys and then apply it to decipher this data.
But now the authors have figured out what molecules were present inside the grains of fresh ice.
They saw that certain organic molecules that were already found in the E ring were also present in the fresh ice grains. This confirms that they were created in the ocean of Enceladus.
They also discovered entirely new molecules that had never before been observed in Enceladus's ice grains.
According to chemists, the newly discovered molecular fragments included aliphatic, (hetero)cyclic esters/alkenes, ethers/ethyls, and presumably nitrogen- and oxygen-containing compounds.
On Earth, these same molecules participate in chains of chemical reactions that ultimately lead to the formation of more complex molecules necessary for life.
“There are many possible pathways from the organic molecules we detected in the Cassini data to potentially biologically significant compounds, raising the possibility that the Moon is habitable,” Dr Nozair said.
“There's a lot more to the data we're looking at now, so we're looking forward to learning more in the near future.”
“These molecules we found in the freshly ejected material prove that the complex organic molecules detected by Cassini in Saturn's E ring are not simply the product of long-term exposure to space, but are also readily available in Enceladus's ocean,” said co-author Dr. Frank Postberg, also from the Free University of Berlin.
results were published this month in the magazine Nature Astronomy.
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N. Khawaja etc.. Detection of organic compounds in freshly ejected ice grains from Enceladus's ocean. Nat Astronpublished online October 1, 2025; doi: 10.1038/s41550-025-02655-y
