The magnetosphere of Saturn is filled with trapped plasma and energy-charged particles that consistently bombard the surface of Enceladus. This plasma mainly consists of charged particles, including water group ions created from high-energy electrons interacting with materials from the plumes. Instruments on NASA’s Cassini spacecraft reveal that on Saturn’s inner icy moons, such as Mimas and Tethys, cold plasma irradiation results in darker reflection spectra and produces blue-tinted features on their surfaces. In contrast, the consequences of plasma bombardment on Enceladus remain largely unexplored and challenging to assess.

“The discovery of complex organic molecules in Enceladus’s environment is crucial for evaluating lunar habitability, indicating that radiation-driven chemistry on the surface and within plumes can yield these molecules.”

The Enceladus plume was first identified in 2005 by NASA’s Cassini spacecraft.

These plumes emerge from a long fracture known as the “Tiger Stripes” located in Enceladus’s Antarctic region.

Originating from a subsurface ocean, the water’s energy to create plumes and heat the ocean arises from gravitational tidal forces exerted by the massive Saturn, which deforms Enceladus’s interior.

Cassini flew through the plume, “sampling” the molecules present, which were found to be rich in salts and a variety of organic compounds.

These findings have captivated astrobiologists since organic compounds found dissolved in underground oceans could lead to prebiotic molecules, the building blocks of life.

However, new insights suggest that radiation from Saturn’s powerful magnetosphere could also contribute to the formation of these organic compounds on Enceladus’s icy surface, prompting questions about their astrobiological significance.

In their research, Dr. Richards and colleagues replicated the ice composition on the surface and along the striped walls of Enceladus’s tiger.

This ice comprises water, carbon dioxide, methane, and ammonia, which were cooled to -200 degrees Celsius.

The researchers then bombarded the ice with ions to mimic the radiation environment surrounding Enceladus.

The interaction of ions with ice components generated various molecular species, including carbon monoxide, cyanate, and ammonium.

It also produced precursor molecules for amino acids, which could support metabolic reactions, aid in cell repair, and facilitate the formation of proteins that transport nutrients in living organisms.

Some of these compounds have been previously identified on Enceladus’s surface, while others were detected in feathers.

“Molecules deemed prebiotic do not necessarily originate from subterranean oceans but can instead form in situ via radiation exposure,” noted Dr. Richards.

“This does not dismiss the potential for the Enceladus seas to be habitable, but it emphasizes the need for caution when interpreting the plume’s composition.”

“Distinguishing between ocean-derived organic matter and molecules formed through radiation interactions with the surface and tiger stripes is extremely complex.”

“Additional data from future missions will be essential, including proposals for the Enceladus mission currently under review as part of the ESA’s Navigation 2050 recommendations for the science program.”

The team’s survey results were announced earlier this month during the EPSC-DPS2025 Joint Meeting in Helsinki, Finland.

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Grace Richards et al. 2025. Water group ion irradiation studies of Enceladus surface analogues. EPSC Abstract 18:EPSC-DPS2025-264; doi:10.5194/epsc-dps2025-264