Cassini spacecraft data reveal volatile organics in particles of one of the icy moons of ring-planet Saturn

Freie Universität Berlin Planetary Sciences research group study published in Monthly Notices of the Royal Astronomical Society

No 291/2019 from Oct 09, 2019

Enceladus, one of the icy moons of the ring-planet Saturn, is ejecting from its south pole a plume of gas and ice grains originating from its subsurface ocean. Dr. Nozair Khawaja and his co-workers from the Freie Universität Berlin Planetary Sciences research group succeeded in detecting volatile, low mass soluble organic species, known precursors for the synthesis of biologically-relevant compounds in Earth’s hydrothermal systems, in the ice grains of the plume. Both very simple, and complex, poorly soluble organic molecules have previously been found in plume gases and ice grains, respectively. The results were recently published in the Monthly Notices of the Royal Astronomical Society.

By analyzing Cassini’s Cosmic Dust Analyzer (CDA) mass spectra of ice particles emitted from Enceladus, and comparing them with laboratory mass spectra of water-organic mixtures, Khawaja’s team has identified organic compounds such as amines, carbonyls, and aromatics in the ice grains. "Some of these compounds are known to take part in terrestrial hydrothermal reactions, synthesizing biologically important organic molecules, such as amino acids", explains Dr. Nozair Khawaja. "Initially dissolved in Enceladus’ ocean, the low mass organic compounds evaporate from the ocean’s surface and then condense onto ice grains as they rise through fractures in Enceladus’ icy crust, before they are emitted into space."

"Evidence points to the existence of extant hydrothermal activity in the depths of Enceladus’ subsurface ocean, with conditions for the synthesis of biologically-relevant organic compounds believed to be similar to those in Earth’s hydrothermal vents on the ocean floor", says the lead author of the study, Dr. Nozair Khawaja of Freie Universität Berlin. "Our findings raise the tantalizing prospect of current habitable conditions in Enceladus’ subsurface ocean."

"After the discovery of large, complex organic molecules, this current finding of low mass organic compounds is one step forward in the investigation of the habitability of Enceladus," co-author Prof. Frank Postberg emphasizes.

The Cassini-Huygens mission is a cooperative project of NASA, ESA, and the Italian Space Agency to investigate Saturn and its moons. Almost 20 years after launch, Cassini plunged into the atmosphere of the ring-planet on September 15, 2017 and burned up. The huge amount of data from the twelve instruments of the mission is still being evaluated.

Publication

N. Khawaja, F. Postberg, J. Hillier, F. Klenner, S. Kempf, L. Nölle, R. Reviol, Z. Zou, R. Srama, Low-mass nitrogen-, oxygen-bearing, and aromatic compounds in Enceladean ice grains, Monthly Notices of the Royal Astronomical Society, Volume 489, Issue 4, November 2019, Pages 5231-5243, doi.org/10.1093/mnra­s/stz2280


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