Enceladus’s subsurface ocean harbors complex organic molecules

Saturn moon is now the only solar system location other than Earth to meet all requirements for microbial life.

Analysis of mass spectroscopy data returned by NASA’s Cassini spacecraft indicates Saturn’s moon Enceladus harbors complex organic molecules in its subsurface ocean, which are ejected through cracks in surface ice.

Cassini made several close flybys of Enceladus, one of the solar system’s top contenders for hosting microbial life, before the spacecraft was plunged into Saturn in September 2017. These flybys found evidence for a subsurface ocean above the moon’s rocky core and detected molecular hydrogen in plumes coming from that ocean.

Scientists believe molecular hydrogen is produced by geochemical interactions between water and rocks in hydrothermal environments, according to a paper on the findings published in the journal Nature.

“Hydrogen provides a source of chemical energy supporting microbes that live in the Earth’s oceans near hydrothermal vents. 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?’ This paper represents the first step in that understanding–complexity in the organic chemistry beyond our expectations!” stated Hunter Waite of the Southwest Research Institute (SwRI), who served as principal investigator for Cassini’s Ion and Neutral Mass Spectrometer (INMS).

Both INMS and Cassini’s Cosmic Dust Analyzer (CDA) measured the contents of Enceladus’s plumes and of material in Saturn’s E ring, which is composed of ice grains from those plumes.

“Previously, we’d only identified the simplest organic molecules containing a few carbon atoms, but even that was intriguing,” Christoper Glenn, also of SwRI and a specialist in extraterrestrial chemical oceanography, noted. “Now, we’ve found organic molecules with masses above 200 atomic mass units. That’s over 10 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.”

By working together, each with their own data set, the CDA and INMS teams achieved a better understanding of the organic chemistry in Enceladus’s ocean than either of the teams would have done with just their own data set, Glenn noted.

In their paper, the researchers recommend a future mission fly through Enceladus’s plumes and use a high-resolution mass spectrometer to analyze the complex organic molecules, with the goal of learning the process by which they formed.


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