Organic Molecules from Enceladus's Subsurface Ocean

An international research team has analyzed data from the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft, obtained during its flyby of Saturn's moon Enceladus. Fresh ice particles ejected from the subsurface ocean were found to contain organic compounds — including aromatic, ether, ester, alkyl compounds, as well as compounds containing nitrogen and oxygen. This discovery strengthens the hypothesis of hydrothermal activity on the ocean floor and Enceladus's potential habitability.

How the Research Was Conducted

The icy and gas jets erupting from fractures near Enceladus's south pole originate from a global subsurface ocean.
During the Cassini–Huygens mission (2004–2017), the probe repeatedly flew through these jets, analyzing the composition of microscopic ice particles.

The fifth flyby (E5) in 2008 proved to be the most informative: the spacecraft passed through the plume at a speed of 17.7 km/s. Such high velocity caused intense ionization of material upon impact, revealing molecular fragments previously undetected during slower flybys (4–12 km/s).

What Was Found in the Ice Particles

Several types of organic structures were identified in the freshly ejected ice crystals:

• Aromatic (aryl) compounds — for example, fragments characteristic of benzene and phenyl rings.
  These structures are stable and likely form in hot hydrothermal systems on the ocean floor.
• Oxygen-containing aliphatic compounds, including aldehydes (e.g., acetaldehyde).
  They may be intermediate products in reactions leading to the formation of amino acids and fatty acids.
• Esters and alkenes — organic groups often involved in synthesis reactions of lipids and other biomolecules.
• Ethers and ethyl groups — compounds capable of serving as "bridges" between larger organic structures.
• Nitrogen and oxygen-containing compounds — possible derivatives of pyridine, pyrimidine, cyano, and carboxyl compounds.
  These fragments are particularly interesting since similar structures are part of the nucleotide bases in DNA and RNA.

Why This Is Important

Previously, Cassini had already found water, salts, carbon dioxide, methane, ammonia, and phosphates on Enceladus — five of the six elements vital for biochemistry (CHNOPS).
Now the presence of a wide range of organic molecules has been confirmed, including more complex ones than simple hydrocarbons.

The totality of this data points to hydrothermal processes in the moon's interior — similar to those occurring in hot springs at the bottom of Earth's oceans. There, as is known, organic reactions concentrate and even primitive life forms can emerge.

Conclusions

• For the first time, esters, alkenes, ethers, and nitrogen-containing compounds have been detected in fresh ice particles ejected directly from Enceladus's subsurface ocean.
• These substances form inside the moon, not on its surface or in Saturn's ring.
• Their chemical composition indicates rich organic chemistry and active geochemistry, including possible hydrothermal reactions.
• The results strengthen the arguments that Enceladus's ocean is one of the most promising targets for the search for extraterrestrial life in the Solar System.

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