Additional organic molecules found in Enceladus’s plume

Molecules including methanol, ethane, and oxygen are present in gaseous plumes emitted from Saturn’s moon Enceladus, a re-analysis of data from the Cassini mission suggests. The findings are published in Nature Astronomy.

The Cassini spacecraft first discovered large plumes of material escaping into space from Enceladus’s southern hemisphere in 2005. These plumes appear to be coming from a subsurface ocean through fissures in the moon’s icy surface. Analyses of data from Cassini’s Ion and Neutral Mass Spectrometer (INMS) collected during flybys in 2011 and 2012 determined the presence of water, carbon dioxide, methane, ammonia, and molecular hydrogen in the samples.

Jonah Peter from the California Institute of Technology, Pasadena, California and others re-examined data processed by the INMS instrument team and compared it to a large library of known mass spectra. Using a statistical analysis technique, which analysed billions of potential compositions of the plume material, they identified that the most likely composition of the plumes is the five already identified molecules along with newly identified hydrocarbons hydrogen cyanide (HCN), acetylene (C₂H₂), propylene (C₃H₆), and ethane (C₂H₆), and traces of an alcohol (methanol) and molecular oxygen. “Our results are agnostic to the presence of hydrogen, which requires analysis of additional INMS data,” they note.

A major finding of the work is the find the definite presence of nitrogen at Enceladus in the form of HCN. “Previous studies have been unable to resolve the HCN abundance due to confounding signals from fragmentation products at mass 28,” they write. 

The authors suggest that this compositionally diverse chemical reservoir under the surface of Enceladus may be consistent with a habitable environment and could potentially support microbial communities. “Together with plausible mineralogical catalysts and redox gradients derived from surface radiolysis, these compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life,” the authors write. The ability of these compounds to support life on Enceladus, however, depends largely on how diluted they may be in the moon’s subsurface ocean, the authors note.