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EPSC-DPS2025: Study Questions Ocean Origin of Organics in Enceladus’s Plumes
- September 12, 2025
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Organic molecules detected in the watery plumes that spew out from cracks in the surface of Enceladus could be formed through exposure to radiation on Saturn’s icy moon, rather than originating from deep within its sub-surface ocean. The findings, presented during the EPSC–DPS2025 Joint Meeting in Helsinki this week, have repercussions for assessing the habitability of Enceladus’s ocean.
‘While the identification of complex organic molecules in Enceladus’s environment remains an important clue in assessing the moon’s habitability, the results demonstrate that radiation-driven chemistry on the surface and in the plumes could also create these molecules,’ said Dr Grace Richards, of the Istituto Nazionale di Astrofisica e Planetologia Spaziale (INAF) in Rome, who presented the results at the meeting.
The plumes were discovered in 2005 by NASA’s Cassini spacecraft. They emanate from long fractures called ‘tiger stripes’ that are located in Enceladus’s south polar region. The water comes from a sub-surface ocean, and the energy to heat the ocean and produce the plumes is the result of gravitational tidal forces from massive Saturn flexing Enceladus’s interior.
Cassini flew through the plumes, ‘tasting’ some of the molecules within them and finding them to be rich in salts as well as containing a variety of organic compounds. As organic compounds, dissolved in a subsurface ocean of water, could build into prebiotic molecules that are the precursors to life, these findings were of great interest to astrobiologists.
However, results of experiments by Richards and her colleagues show that the exposure to radiation trapped in Saturn’s powerful magnetosphere could trigger the formation of these organic compounds on Enceladus’s icy surface instead. This calls into question their astrobiological relevance.
Richards, with funding from Europlanet, visited facilities at the HUN-REN Institute for Nuclear Physics in Hungary, where she and colleagues simulated the composition of ice on the surface and in the walls of Enceladus’s tiger stripes. This ice contained water, carbon dioxide, methane and ammonia and was cooled to -200 degrees Celsius. Richards’s team then bombarded the ice with ions – atoms and molecules stripped of an electron – to replicate the radiation environment around Enceladus. The ions reacted with the icy components, creating a whole swathe of molecular species, including carbon monoxide, cyanate and ammonium. They also produced molecular precursors to amino acids, chains of which form proteins that drive metabolic reactions, repair cells and convey nutrients in lifeforms.
Some of these compounds have previously been detected on the surface of Enceladus, but others have also been identified in the plumes.
‘Molecules considered prebiotic could plausibly form in situ through radiation processing, rather than necessarily originating from the subsurface ocean,’ said Richards. ‘Although this doesn’t rule out the possibility that Enceladus’s ocean may be habitable, it does mean we need to be cautious in making that assumption just because of the composition of the plumes.’
Understanding how to differentiate between ocean-derived organics and molecules formed by radiation interacting with the surface and the tiger stripes will be highly challenging. More data from future missions will be required, such as a proposed Enceladus mission that is currently under consideration as part of the Voyage 2050 recommendations for the European Space Agency (ESA)’s science programme up until the middle of the century.
Further information
EPSC-DPS2025-264 Water-Group Ion Irradiation Studies of Enceladus Surface Analogues
Grace Richards, Richárd Rácz, Sándor Kovács, Victoria Pearson, Geraint Morgan, Manish Patel, Simon Sheridan, Duncan Mifsud, Béla Sulik, Sándor Biri and Zoltán Juhász, https://doi.org/10.5194/epsc-dps2025-264
This study was supported by the Europlanet 2024 RI Transnational Access programme, which received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149. Funding was also received from the COST Actions CA20129 MultIChem and CA22133 PLANETS, supported by COST (European Cooperation in Science and Technology). Grace Richards is grateful for doctoral funding from the Research England ‘Expanding Excellence in England’ fund (grant code 124.18).
Images
An artist’s impression of plumes erupting onto the surface of Enceladus. Its fellow moon Titan is seen in the sky, and the distant Sun beyond. Image credit: ESA/Science Office.
Enceladus, imaged by the Cassini spacecraft. Image credit: NASA/JPL/Space Science Institute.
Enceladus’s plumes seen spraying up from the tiger stripes. Image credit: NASA/JPL/Space Science Institute.
Contacts
Grace RichardsIstituto Nazionale di Astrofisica (INAF), Rome, Italygrace.richards@inaf.it
EPSC-DPS2025 Press Officepress@europlanet.org
Notes for Editors
About the Joint Meeting of the Europlanet Science Congress and the Division of Planetary Sciences (EPSC-DPS)
The Europlanet Science Congress (EPSC), established in 2006 as the European Planetary Science Congress, is the largest planetary science meeting in Europe. It covers the entire range of planetary sciences, with an extensive mix of talks, workshops and poster sessions, as well as providing a unique space for networking and exchanges of experiences.
EPSC joined forces for the first time with the American Astronomical Society’s Division for Planetary Sciences (DPS) for a joint meeting in Nantes, France, in 2011. This was followed by DPS-EPSC 2016 in Pasadena, EPSC-DPS 2019 in Geneva, and the return to the United States for the DPS-EPSC 2023 meeting in San Antonio. This year will mark the third iteration of a joint European-based meeting. The intent of the joint meetings is not only to connect the European and North American planetary science communities, but also to consolidate two major meetings and motivate planetary scientists from all over the globe to attend.
Follow on social media (Bluesky, X and LinkedIn) with the hashtag #EPSC-DPS2025 for updates on the meeting.
About Europlanet
Europlanet (europlanet.org) is a non-profit association and membership organisationthat provides the planetary science community with access to research infrastructure, services and training. The Europlanet Association Sans But Lucratif (AISBL), established in 2023, builds on the heritage of a series of projects funded by the European Commission between 2005 and 2024 (Grant Numbers 871149, 654208, 228319 and RICA-CT-2004-001637) to support the planetary science community in Europe and around the world.
About the DPS
The Division for Planetary Sciences (DPS), founded in 1968, is the largest special-interest Division of the American Astronomical Society (AAS). Members of the DPS study the bodies of our own solar system, from planets and moons to comets and asteroids, and all other solar-system objects and processes. With the discovery that planets exist around other stars, the DPS has expanded its scope to include the study of extrasolar planetary systems as well. The American Astronomical Society (AAS), established in 1899, is the major organization of professional astronomers in North America. The mission of the AAS is to enhance and share humanity’s scientific understanding of the universe as a diverse and inclusive astronomical community, which it achieves through publishing, meeting organization, science advocacy, education and outreach, and training and professional development.
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