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Plumes of Enceladus water vapor. Image via NASA / JPL / Space Science Institute
Saturn's moon Enceladus may be tiny, but it has the potential to help answer one of the biggest questions in our lives: are we alone? NASA's Cassini mission has taken a close look at this enigmatic world and discovered that it was incredibly active, at least geologically, with huge plumes of water vapor that emerged from a riot. salty underwater global ocean under the outer ice crust. Cassini actually flew through these plumes, sampling them for analysis. We already knew that it contained water vapor, ice particles, salts, hydrogen and simple organic compounds. Now, a new analysis of the Southwest Research Institute (SwRI) published on June 27, 2018, shows that plumes also contain many more complex organic compounds. This does not mean yet proof of life itself, but it shows more clearly that Enceladus' ocean meets all the demands of life.
The research team was led by Frank Postberg and Nozair Khawaja of the University of Heidelberg, Germany. As noted Postberg:
it is the very first detection of complex organic compounds from an extraterrestrial aquatic world.
Chart of organic-rich bubbles rising to the surface of deeper into the ocean. Image via ESA / F. Postberg et al (2018).
Diagram depicting the interior of Enceladus. Ocean water and organic matter are found on the surface through cracks in the outer ice sheet. Image by NASA / JPL-Caltech / Institute for Space Science / LPG-CNRS / Nantes-Angers / ESA
Organic compounds are quite large and complex, as Khawaja added:
We found large molecular fragments showing typical structures very complex organic molecules. These huge molecules contain a complex network often constructed from hundreds of carbon atoms, hydrogen, oxygen, and probable nitrogen that form ring-shaped substructures. and chain
SwRI scientists analyze Cassini's mass spectrometry data. As explained by Dr. Christopher Glein, a space scientist specializing in extraterrestrial chemical oceanography (and co-author of the new article in the scientific journal Nature ):
We are, once again, blown away by Enceladus. Previously, we only identified the simplest organic molecules containing a few carbon atoms, but even that was very intriguing. We have now found organic molecules with masses greater than 200 atomic mass units. It's more than ten times heavier than methane. With complex organic molecules emanating from its ocean of liquid water, this moon is the only body outside the Earth known to simultaneously satisfy all the fundamental requirements for life as we know it.
Diagram of an interior cross-section of the Enceladus crust, showing hydrothermal vents on the ocean floor and plumes of water vapor that escape through cracks to the surface. Image by NASA-GSFC / SVS / NASA / JPL-Caltech / Southwestern Research Institute.
The heavy organic fragments discovered are believed to be remnants of larger perhaps thousands of atomic mass units. The larger ones were broken into smaller fragments when they collided with the instrument analyzing Cassini dust at speeds of about 18,640 miles per hour (30,000 kilometers per hour). These large organic molecules can only be created by complex chemical processes, including life or hydrothermal activity.
The discovery of such complex organic compounds is exciting, especially when they are found in an ocean of hot water. Organic substances like this one can be formed abiotically, lifeless, or can be relics of organisms themselves. In the case of Enceladus, we do not know yet, or both, but it is tempting. There is also Cassini evidence for active geothermal hot air sources on the ocean floor, just like those on Earth. Here, these vents swarm with a variety of small organisms. Would it be the same for Enceladus? The Cassini mission itself may be over, but the science continues, as Glein notes:
Even after its end, the Cassini spacecraft continues to teach us the potential of Enceladus to advance the field of astrobiology in an oceanic world. This article demonstrates the value of teamwork in planetary science. The INMS and CDA teams collaborated to achieve a deeper understanding of the organic chemistry of the Encelade Underground Ocean with only one set of data.
Molecular hydrogen previously detected in plumes is another important clue, forming through geochemical interactions between water and rocks in hydrothermal environments. According to Dr. Hunter Waite, principal investigator of INMS and co-author of the new paper, [traduction]
hydrogen provides a source of chemical energy that supports the microbes that live in the oceans of the Earth near hydrothermal chimneys. Once you have identified a potential source of food for microbes, the next question to ask is: "What is the nature of complex organic compounds in the ocean?" This article represents the first step in this understanding – complexity organic chemistry beyond our expectations!
The results also suggest a "film" rich in organic matter on the top of the ocean. Gas bubbles, rising through dozens of kilometers of ocean water, could bring up organic matter where they form a thin film floating on the surface of the ocean, just beneath the surface. 39, outer glazed envelope. From the abstract:
We report here observations of emitted ice grains containing concentrated and complex macromolecular organic matter having molecular weights greater than 200 atomic mass units. The data constrain the macromolecular structure of the organic compounds detected in the ice grains and suggest the presence of a thin film rich in organic matter above the water table, where the organic nucleation nuclei generated by the bursting bubbles allow to explore the organic inventory of Enceladus. in increased concentrations.
A global vision of Enceladus. Image via NASA / JPL / Space Science Institute
Not only are these discoveries exciting in and of themselves, but they also have implications for Enceladus' future exploration, and return mission concepts. are now on the drawing boards. As Glein noted:
The findings of the paper also have great significance for the next generation of exploration. A future spacecraft could fly through Enceladus plumes, and analyze these complex organic molecules using a high-resolution mass spectrometer to help us determine how they were made. We must be cautious, but it is exciting to think that this discovery indicates that the biological synthesis of organic molecules on Enceladus is possible.
Bottom line: Thanks to Cassini, Enceladus has long been considered one of the best places in the solar system to look for evidence of extraterrestrial life. Is there anything swimming in this warm but dark ocean? Perhaps, and this new discovery of complex organic compounds enhances the possibility. Even if only something like bacteria, finding life in the ocean of Enceladus would be one of the most exciting discoveries in history.
Source: Macromolecular Organic Compounds from the Depths of Enceladus
SwRI / Via ESA
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