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<\/p>\nLocated around Saturn is the icy moon Enceladus \u2014 one of the most interesting and potentially habitable moons in the solar system. NASA\u2019s Cassini mission extensively studied Saturn and its moons from 2004 to 2017 and, in 2005, revealed large geyser-like jets extending from Enceladus\u2019 south pole.<\/p>\n
Later studies would suggest that a massive subsurface ocean was responsible for the jets, which are primarily comprised of water ice. Now, in a new study using archival Cassini data, a team of scientists has discovered a plethora of new complex organic molecules within these jets. The presence of the new molecules in the jets proves that complex chemical reactions are occurring in Enceladus\u2019 subsurface ocean.<\/p>\n<\/p>\n
\u201cCassini was detecting samples from Enceladus all the time as it flew through Saturn\u2019s E ring. We had already found many organic molecules in these ice grains, including precursors for amino acids,\u201d explained Nozair Khawaja, the study\u2019s lead author.<\/p>\n
Saturn\u2019s E ring is the faint ring of ice grains created by the ice grains spewed out of Enceladus\u2019 south pole. The ring traces the moon\u2019s orbit, and as the ice grains orbit Saturn, they are subjected to intense radiation from the Sun and Saturn\u2019s magnetic field.<\/p>\n
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In this image from Cassini, Enceladus can be seen in the center, with the massive E ring extending above and below the moon. (Credit: NASA\/JPL-Caltech\/Space Science Institute)<\/p>\n
However, these ice grains are hundreds of years old, and given their continuous radiation exposure, are often significantly weathered from their initial states. To better assess the processes within Enceladus\u2019 ocean, scientists needed to investigate the ice grains immediately after their ejection from the moon\u2019s south pole.<\/p>\n
Fortunately, in 2008, Cassini flew directly through the plume from the south polar jets, using its Cosmic Dust Analyzer (CDA) to collect data on ice grains just minutes after their ejection. The ice grains hit the CDA at around 18 km\/s. The speed at which the ice grains impacted the CDA proved to be important in Khawaja et al.\u2019s analysis.<\/p>\n
\u201cThe ice grains contain not just frozen water, but also other molecules, including organics. At lower impact speeds, the ice shatters, and the signal from clusters of water molecules can hide the signal from certain organic molecules. But when the ice grains hit CDA fast, water molecules don\u2019t cluster, and we have a chance to see these previously hidden signals,\u201d Khawaja said.<\/p>\n
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Cassini\u2019s Cosmic Dust Analyzer. (Credit: ESA\/NASA\/JPL\/Space Science Institute)<\/p>\n
Several of the molecules detected by the CDA during Cassini\u2019s 2008 plume flyby were also detected in later flybys of the E ring, confirming that the E ring\u2019s ice grains originate from Enceladus\u2019 subsurface ocean.<\/p>\n
\u201cThese molecules we found in the freshly ejected material prove that the complex organic molecules Cassini detected in Saturn\u2019s E ring are not just a product of long exposure to space, but are readily available in Enceladus\u2019s ocean,\u201d said Frank Postberg, a co-author of the study.<\/p>\n
What\u2019s more, the team found new molecules, including aliphatic esters\/alkenes, heterocyclic esters\/alkenes, ethers\/ethyl, and nitrogen- and oxygen-bearing compounds. These complex organic molecules, when involved in chains of chemical reactions, can produce other complex molecules required for life.<\/p>\n
\u201cThere are many possible pathways from the organic molecules we found in the Cassini data to potentially biologically relevant compounds, which enhances the likelihood that the moon is habitable. There is much more in the data that we are currently exploring, so we are looking forward to finding out more in the near future,\u201d says Nozair.<\/p>\n
Future missions to Enceladus are expected to further explore the moon\u2019s subsurface ocean and habitability. The European Space Agency (ESA) announced in 2024 that Enceladus was one of the agency\u2019s top targets for a future mission to Saturn. Studies for the mission have begun, with the spacecraft expected to land on and collect samples from the moon\u2019s south polar region.<\/p>\n
Enceladus hosts some of the most habitable conditions in the solar system \u2014 liquid water, a source of energy, and complex reactions and molecules. As space technology advances and current missions like ESA\u2019s Jupiter Icy Moons Explorer (JUICE) further inform scientists on icy moons and their nature, Enceladus is becoming a clear target for humanity\u2019s search for life outside of Earth.<\/p>\n<\/p>\n