Enceladus Organic Compounds: New Evidence From Cassini’s Fresh Ice Grain Samples

A Closer Look at Enceladus’ Plumes

Researchers took a new look at data from NASA’s Cassini mission and found organic compounds in the icy plumes of Saturn’s moon Enceladus that had never been detected before. The ice grains came from the ocean hidden beneath the moon’s frozen shell. Along with molecules seen in earlier studies, the team also found new ones that point toward active chemical or biochemical processes.

Sampling Ice Only Minutes Old

Cassini collected the ice grains during a fast flyby, only 13 miles or 21 kilometers above the surface. This is the first time scientists have observed such a wide mix of organics in freshly ejected particles from Enceladus’ subsurface ocean. The results, published in Nature Astronomy, add strong support to the idea that complex chemical activity is happening under the moon’s icy crust. These reactions could create compounds that play important roles in biological systems.

The team built on earlier work by studying grains collected during a direct plunge through the plume. It provided the closest possible look at the moon’s ocean without diving into it.

“Earlier, we found organics in ice grains that had spent years in Saturn’s radiation environment,” said Nozair Khawaja of Freie Universität Berlin, the study’s lead author. “These new samples were only minutes old, carried straight from the ocean below the surface.”

Fresh Material from the Source

Previous studies already showed nitrogen- and oxygen-bearing organics in particles from Saturn’s E ring. The E ring is supplied by material that escapes from Enceladus. This new research focused only on grains taken directly from a plume, giving scientists a clearer view of the moon’s interior chemistry.

“These molecules in the fresh plume material show that the complex organics Cassini detected in Saturn’s E ring aren’t just the result of long exposure to space,” said coauthor Frank Postberg. “They exist in the ocean itself.”

High-Speed Impacts Revealed Hidden Chemistry

The data came from 2008, when ice particles slammed into Cassini’s Cosmic Dust Analyzer at about 11 miles per second, or 18 kilometers per second. The impact vaporized the grains and ionized much of the material. The instrument’s mass spectrometer then examined the ions to determine their makeup.

The team studied tiny fragments, smaller than a thousandth of a millimeter and even smaller than a flu virus. In those fragments, they found organic compounds that had never been identified in Enceladus’ plume before.

The newly detected molecules include aliphatic and cyclic esters and ethers, some with double bonds. Together with the previously known aromatic, nitrogen-, and oxygen-bearing organics, they form building blocks that can support more complex chemical reactions. These reactions are important to astrobiology and help narrow down where we search for life in the solar system.

Cassini’s Lasting Legacy

After this plume flyby, Cassini continued to explore the Saturn system for nearly another decade. Managed by NASA’s Jet Propulsion Laboratory in Southern California, the spacecraft delivered a wealth of data that scientists are still analyzing today.