Enceladus\u2019 status as a target in the search for life keeps rising. We\u2019ve known for years that plumes erupting from the ocean under the moon\u2019s icy shell contain important organic compounds related to life. Now, researchers have found another chemical in the plumes which is not only highly toxic but also critical in the appearance of life. <\/p>\n
<\/p>\n The Cassini spacecraft spent 13 years in the Saturn system before ending its mission in 2017. Among its many discoveries were plumes erupting from Saturn\u2019s moon Enceladus. The images of the plumes are iconic. <\/p>\n But what the plumes contain is what really captured scientists\u2019 attention. Cassini found compounds like carbon dioxide, methane, water, and ammonia. It also found salts, indicating that the ocean is salty. Now, researchers working with the Cassini data have identified hydrogen cyanide in the plumes. <\/p>\n Most of us know that hydrogen cyanide is extremely poisonous. It played a role in one of humanity\u2019s most heinous episodes. But hydrogen cyanide (HCN) has another side to it, one that scientists think is important for the appearance of life. It may act as a precursor to nucleic acids and amino acids. <\/p>\n \u201cOur work provides further evidence that Enceladus is host to some of the most important molecules for both creating the building blocks of life and for sustaining that life through metabolic reactions,\u201d said Jonah Peter, a doctoral student at Harvard University. Peter is the lead author of new research published in Nature Astronomy. \u201cNot only does Enceladus seem to meet the basic requirements for habitability, we now have an idea about how complex biomolecules could form there, and what sort of chemical pathways might be involved,\u201d added Peter.<\/p>\n Amino acids are important building blocks of life. They\u2019re the basic unit of proteins, which are long chains of amino acids. There are over 500 hundred proteins in nature, but there are only 22 that are part of the genetic code. HCN is extremely versatile and plays a role in all amino acids, so its presence in Enceladus\u2019 oceans is intriguing. <\/p>\n \u201cThe discovery of hydrogen cyanide was particularly exciting because it\u2019s the starting point for most theories on the origin of life,\u201d Peter said.<\/p>\n Scientists have been working with Cassini\u2019s data for years, but previous investigations into the plumes didn\u2019t show any HCN. \u201cThe most recently published list of neutral gas species confirmed in the plume consists of only H2O, CO2, CH4, NH3 and H2,\u201d the authors write in their paper. <\/p>\n Determining what chemicals Cassini sensed in Enceladus\u2019 was the job of the Ion and Neutral Mass Spectrometer (INMS), an important part of Cassini\u2019s instrument suite. There are only small amounts of some of these chemicals, and they\u2019re difficult to differentiate in the INMS\u2019s data. \u201cDifficulty in resolving minor plume constituents stems from the large number of plausible compounds relative to the low mass resolution of INMS.\u201d <\/p>\n Scientists take the data from INMS and try and match it with models of known chemicals and ratios. That\u2019s complex work. \u201cModels of INMS spectra suffer from an additional complexity in that the signals produced by individual molecules are not necessarily linearly independent,\u201d the authors explain. \u201cAs such, there may be multiple different combinations of species that appear to fit the data equally well.\u201d <\/p>\n That means it took some sleuthing to find the HCN. And no matter how hard the researchers tried to find an alternative explanation for what they saw, they couldn\u2019t. <\/p>\n \u201cThere are many potential puzzle pieces that can be fit together when trying to match the observed data,\u201d Peter said. \u201cWe used math and statistical modelling to figure out which combination of puzzle pieces best matches the plume composition and makes the most of the data without overinterpreting the limited dataset.\u201d<\/p>\n \u201cThe more we tried to poke holes in our results by testing alternative models,\u201d Peter added, \u201cthe stronger the evidence became. Eventually, it became clear that there is no way to match the plume composition without including hydrogen cyanide.\u201d<\/p>\n The discovery of HCN in Enceladus\u2019 plumes is important because it\u2019s kind of like a \u2018Swiss army knife\u2019 of prebiotic molecules. Its versatility means it can be assembled in many different ways, leading to the development of many different amino acids. \u201cHCN polymerization is implicated in a number of potential pathways for the formation of nucleobases and amino acids,\u201d the researchers write in their paper. <\/p>\n There has to be some feedback between the plumes and the ocean for the HCN to work its chemical magic. Material from the ocean can be deposited on the icy surface, where it is subjected to photochemical processing. If there\u2019s enough UV striking some of these materials, then the HCN and other components of the plumes could produce RNA and amino acid precursors. Then these newly-produced chemicals could work their way back through the ice to the ocean. <\/p>\n Scientists don\u2019t know for certain if that\u2019s happening. \u201cWhether this type of chemistry is efficient under Enceladus-like conditions could be explored in future experimental studies,\u201d the researchers explain, \u201cwhile more detailed examination of Enceladus\u2019 oceanic material will require future robotic missions.\u201d<\/p>\n While finding HCN at Enceladus is an exciting development, it\u2019s not all the researchers found.<\/p>\n Previous research found carbon dioxide, methane, and hydrogen in Enceladus\u2019 plumes. Together, they suggest that methanogenesis is taking place in the moon\u2019s ocean. Methanogenesis is the metabolic process that produces methane, and methanogens are the life forms that perform methanogenesis. Methanogenesis is common on Earth and only takes place in low-oxygen environments. Methanogens originated on early Earth, and finding these chemicals at Enceladus suggests that primitive methanogens could be active in the moon\u2019s ocean. <\/p>\n But in this new research, Peter and his co-researchers found an array of oxidized compounds. This indicates that oxygen is active in the ocean and that there are different energetic pathways life could be using. Life forms that use oxygen have far more energy at their disposal than ones that rely on methanogenesis. <\/p>\n \u201cIf methanogenesis is like a small watch battery, in terms of energy, then our results suggest the ocean of Enceladus might offer something more akin to a car battery, capable of providing a large amount of energy to any life that might be present,\u201d said JPL\u2019s Kevin Hand, co-author of the study and principal investigator of the effort that led to the new results.<\/p>\n Enceladus is becoming a more and more intriguing place. Its chemistry suggests that there\u2019s everything needed for life in the moon\u2019s ocean. There may already be life present. \u201cIn aggregate, the results presented here indicate that Enceladus is host to a multiphasic and compositionally diverse chemical environment that is consistent with a habitable subsurface ocean,\u201d the authors write.<\/p>\n But there\u2019s still a lot we don\u2019t know. So while these results are fascinating, a deeper understanding is still beyond our reach. <\/p>\n We need a mission to Enceladus. <\/p>\n![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2023\/12\/Enceladus-Plume-Chemistry.jpg\")
![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2023\/12\/Enceladus-HCN.png\")
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