A new analysis of data from the US Cassini probe has found evidence of previously undetected organic compounds in a jet of icy particles ejected from the ocean that lies beneath the frozen shell of Saturn’s moon Enceladus. The researchers not only detected molecules that they had already found before, but also new ones that indicate a potential path to chemical or biochemical activity. The ice grains were captured just 21 kilometers above the moon’s surface, and it was the first time scientists had observed such a diverse array of organic matter on fresh particles ejected from Enceladus’ subsurface waters. The findings, published in the journal Nature Astronomy, signal an important step toward confirming active organic reactions beneath Enceladus’ surface. This kind of chemical activity could support compounds that are important for biological processes and are a necessary component of life on Earth. We already reported on these discoveries in early October, but now new details are available. The October text was about that scientists reanalyzed the data years later and found new organics and what it means for the European mission under consideration. The new information goes deeper into the scientific interpretation of the newly identified molecules, their chemical properties, their age and the physical process of detection.
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In addition to the increasing variety of organics detected, the current new study adds a new layer to earlier findings from analyzes of particles collected by Cassini as it flew right through the jet, which NASA is calling the second best thing to this moon’s ocean plunge. “Previously, we detected organic matter on ice grains that were several years old and could potentially have been altered by the intense radiation environment in which they move,” explained Nozair Khawaja of Freie Universität Berlin, lead author of the study, adding: “These new organics were barely a few minutes old, and we discovered them in ice that was fresh from the ocean beneath Enceladus’ surface.“
Scientists already knew from earlier analyzes of data from Cassini that organic substances containing nitrogen and oxygen are found in particles in Saturn’s E ring. The E ring is a faint but broad outer band around the planet that is supplied by icy material that is dispersed from Enceladus’ jets. But the new research analyzed ice grains from the jet itself — in other words, the grains found closest to their subsurface origin. “These molecules we discovered in the freshly ejected material confirm that the complex organic molecules in Saturn’s E ring are not simply the product of long exposure to the cosmic environment, but are widely available in Enceladus’ ocean.” mentioned the co-author of the study, Frank Postberg, who is also from the Freie Universität in Berlin.
The data was collected and sent to Earth in 2008 when icy particles hit the Cosmic Dust Analyzer onboard. Besides coming straight from the jet, these ice crystals had another advantage. They were crushed into tiny pieces when the spacecraft hit the instrument during a brisk flyby at about 18 kilometers per second relative to the moon. The energy of the impact vaporized the ice grains and ionized a substantial part of them. These ions were analyzed by the instrument’s mass spectrometer, which evaluated their chemical composition.
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The authors of the study were able to analyze even the smallest fragments that were smaller than a thousandth of a millimeter, they were even smaller than the flu virus. And yet, experts identified organic compounds in them that no one had seen before in jet particles. The newly detected compounds contain substances from families of aliphatic and cyclic esters and ethers, some of which have double bonds in their molecular structures. Together with the confirmed aromatic, nitrogen and oxygen compounds, these substances may be building blocks that support chemical reactions and processes that could lead to more complex organic processes, the kind that interest astrobiologists and narrow the focus of where we should look for life in the Solar System. After flying through the jet, Cassini, operated by Southern California’s Jet Propulsion Laboratory, fared well. She explored the complex Saturn system for almost another ten years.
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