New organic molecules discovered on Saturn’s moon Enceladus

Two years ago, the Cassini probe was sent plummeting into Saturn to its fiery demise – but researchers are still finding new discoveries in the data it sent back. Now, scientists from the Free University Berlin have reported findings from the CDA, the “Cosmic Dust Analyzer,” which was on board Cassini. This instrument was developed in Germany and was designed to study very small particles.

The CDA could detect particles with a velocity of 5 kilometers per second and a mass of only 1013 grams (a ten-millionth of a millionth of a gram, which corresponds to a size of two-thousands of a millimeter). In addition to the particle velocity and particle size (10 nanometers to 100 micrometers), it also determined the electrical charge of the particles and their basic composition.

But what exactly did the CDA find when the Cassini probe passed Saturn’s moon Enceladus? The CDA didn’t directly identify the substances; its data has to be interpreted. To do this, in a new study, researchers first performed experiments to determine what substances would deliver the same results as those that Cassini had transmitted back to Earth. Then the scientists compared the results with those of a second instrument on board the probe, the INMS (Ion and Neutral Mass Spectrometer), and determined the best candidates.

The best fits turned out to be low-mass amines (NH3 groups) and carbonyls (CO groups) – typical components of amino acids, the building blocks of life. “Some of the organic compounds that were found are known to take part in terrestrial hydrothermal reactions, synthesizing biologically important organic molecules, such as amino acids,” explains Dr. Nozair Khawaja, lead author of the study. “The low-mass organic compounds, initially dissolved in the ocean of Enceladus, the icy moon, evaporate at the surface of the ocean and then condense onto ice particles as they rise through cracks in Enceladus’s icy crust, before they are finally ejected into space.”

What does that mean? “The evidence,” Khawaja explains further, “indicates that the existing hydrothermal activity in the depths of the Enceladus’s subsurface ocean enables the synthesis of biologically relevant organic compounds. The conditions for the formation of these organic compounds could be similar to those in hydrothermal vents on ocean floors on Earth. Our findings raise the exciting prospect of conditions of life for organisms in Enceladus’s subsurface ocean.”

“After the discovery of large, complex organic molecules, the current findings on low-mass organic compounds are another important step in the research on the habitability of Enceladus,” emphasizes co-author Prof. Frank Postberg.

In 2007, Cassini took this photo of plumes ejecting matter into space at the southern pole of Enceladus (image: NASA/JPL/Space Science Institute)
How the components of amino acids got into the Enceladus plumes (image: NASA/JPL-Caltech)

 

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