“We are, yet again, blown away by Enceladus. Previously we’d only identified the simplest organic molecules containing a few carbon atoms, but even that was very intriguing,” said Southwest Research Institute’s Christopher Glein, a space scientist specializing in extraterrestrial chemical oceanography in June of 2018.
“Now we’ve found organic molecules with masses above 200 atomic mass units,” Glein added. “That’s over ten times heavier than methane. With complex organic molecules emanating from its liquid water ocean, this moon is the only body besides Earth known to simultaneously satisfy all of the basic requirements for life as we know it.”
In a new 2019 effort, reported today by Phys.org, a team of researchers, one with the University of Maryland the other with Southwest Research Institute, sought to determine why Enceladus is unique in the Saturn system by designing their model to mimic the behavior of Saturn and its moons over the course of the past 4.5 billion years, which showed that Enceladus developed a subsurface ocean because of its unique gravitational interactions with the other moons—they forced Enceladus into an oblong orbit.
The 2018 effort used mass spectrometry data from NASA’s Cassini spacecraft, revealing large, carbon-rich organic molecules are ejected from cracks in the icy moon’s surface (The NASA/JPL-Caltech image above shows NASA’s Cassini spacecraft flying through a plume ). Southwest Research Institute scientists think chemical reactions between the moon’s rocky core and warm water from its subsurface ocean are linked to these complex molecules.
Some backstory: prior to its deorbit in September of 2017, Cassini sampled the plume of material emerging from the subsurface of Enceladus. The Cosmic Dust Analyzer (CDA) and the SwRI-led Ion and Neutral Mass Spectrometer (INMS) made measurements both within the plume and Saturn’s E-ring, which is formed by plume ice grains escaping Enceladus’ gravity.
During Cassini’s close flyby of Enceladus on Oct. 28, 2015, INMS detected molecular hydrogen as the spacecraft flew through the plume. Previous flybys provided evidence for a global subsurface ocean residing above a rocky core. Molecular hydrogen in the plume is thought to form by the geochemical interaction between water and rocks in hydrothermal environments.
“Hydrogen provides a source of chemical energy supporting microbes that live in the Earth’s oceans near hydrothermal vents,” said SwRI’s Hunter Waite, INMS principal investigator. “Once you have identified a potential food source for microbes, the next question to ask is ‘what is the nature of the complex organics in the ocean?”
2018 SWRI findings also have great significance for the next generation of exploration, Glein said. “A future spacecraft could fly through the plume of Enceladus, and analyze those 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 ponder that this finding indicates that the biological synthesis of organic molecules on Enceladus is possible.”