Natural "batteries" made Mars organic

"Daybreak at Gale Crater". Computer generated image of Mars between darkness and daylight (credit: NASA/JPL-Caltech)

Evidence of organic material on Mars repeatedly cause euphoria among researchers and science enthusiasts alike. Perhaps, it is hoped, the evidence of life on Mars could also condense with the traces. An international team of researchers led by Andrew Steele of the Carnegie Institution of Washington in Washington D.C., of which Liane G. Benning from the Helmholtz Centre Potsdam German Research Centre for Geosciences - GFZ as well as Richard Wirth and Anja Schreiber from Benning's group were a a part, have now investigated the origin of the organic carbon in three Mars meteorites. The scientists suspect that the carbon was formed by electrochemical reactions between volcanic minerals and briny liquids, they report in a study published in the journal Science Advances. They suggest a possible "paradigm shift" in the search for life on other planets and the explanation of evolutionary processes on Earth.

Liane G. Benning: "We have spent more than five years researching these unique and valuable samples of Mars meteorites. This study was only possible with the high-resolution electron microscopes here at the German Research Centre for Geosciences and their analytical capabilities".

With a few exceptions, organic carbons comprise the compounds of carbon with itself or other elements such as hydrogen. They are regarded as basic building blocks for the processes of life as we know it and can arise through biological processes, but also through inanimate chemical processes. How the organic carbon components found in the three Mars meteorites called Tissint, Nakhla and NWA 1950 were formed was revealed by the research team using modern electron microscopic, spectroscopic, spectrometric and X-ray investigations. The team has developed a hypothesis: Similar to a battery, an electrical voltage was generated on Mars when metal-containing material in the form of igneous rock collided with a briny solution of liquid. The energy from this "galvanic" process was sufficient to produce, in a multi-stage chemical reaction, the organic carbon compounds.

The results are based on research carried out in 2012, when Steele and his team were able to prove that the organic carbon in the meteorites actually comes from Mars and not from a pollution on Earth. They also found out that the carbon is not of biological origin. The study now published aimed to find out where the organic carbon came from instead.

The fact that nature apparently provides enough energy for the process described is of great importance for research in the field of astrobiology. A discovery of organic material does not necessarily have to be an indication of life. In principle, the described process is possible wherever volcanic material comes into contact with salty liquids. For example, similar processes could have taken place on Earth or on Saturn's and Jupiter's moons Enceladus and Europa.

The new findings are also relevant for natural phenomena observed on Mars, such as the occurrence of methane in its atmosphere or refractory organic material found in rock samples by the Curiosity rover. The results of the current analyses of Mars meteorites on Earth agree with what the rover robot found on the surface of the 'red planet'. Only the "powerful combination of robotic and laboratory analyses" could help to establish their hypothesis, the researchers write. Benning and her colleagues now want to validate this hypothesis by carrying out a specific robot-assisted investigation on samples returned from Mars and subsequent laboratory experiments.

The researchers have dedicated their study to Erik Hauri of the Carnegie Institution, who participated in the work and died in September. In 2008, the geochemist Hauri was involved in the discovery of traces of water on the moon. In 2011 he was able to show that the moon accommodates much larger quantities of water than previously thought. This raised far-reaching questions about the formation theory of the moon and Earth-like planets.

Original study: Steele, A., Benning, L. G., Wirth R., Siljeström, S., Fries, M.D., Hauri, E., Conrad, P.G., Rogers, K., Eigenbrode, J., Schreiber, A., Needham, A., Wang, J.H., McCubbin, F.M., Kilcoyne D., Rodriguez Blanco, J.D., 2018. Organic synthesis on Mars by electrochemical reduction of CO2. Science Advances. DOI: 10.1126/sciadv.aat5118

Scientific contact:
Prof. Dr. Liane G. Benning
Section Head Interface Geochemistry
Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
14473 Potsdam
Phone: +49 331 288-28970
Twitter: @LianeGBenning

Media contact:
Dipl.-Phys. Philipp Hummel
Referee Media and Communications
Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
14473 Potsdam
Phone: +49 331 288-1049
Twitter: @gfz_potsdam

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