NASA’s Curiosity rover has measured the total organic carbon content of rocks on Mars for the first time using data from the rover.
“Total organic carbon is one of several measurements [or indices] that help us understand how much material is available as feedstock for prebiotic chemistry and potentially biology,” explained Jennifer Stern of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“We found at least 200 to 273 parts per million of organic carbon. This is comparable to or even more than the amount found in rocks in very low-life places on Earth, such as parts of the Atacama Desert in South America, and more than has been detected in Mars meteorites.”
A carbon atom bound to an atom of hydrogen is organic carbon. Organic molecules are the basis for life and are built and used by every known species.
It is critical to note that the presence of organic carbon on Mars does not prove the presence of life, since it is also possible that organic carbon comes from non-living sources, such as meteorites, and volcanoes, or is formed by surface reactions.
Prior measurements have detected organic carbon on Mars, but they were either limited to a few compounds or only represented a portion of the organic carbon present in the rocks.
These new measurements reveal the amount of organic carbon in the rocks.
Mars’ surface may be inhospitable for life now, but billions of years ago the climate was similar to Earth’s, with thicker atmospheres and rivers filled with liquid water.
Several scientists agree that organic carbon could have sustained Martian life if it ever existed since liquid water is indispensable for life as we know it.
Mars’ habitability and climate are being examined by Curiosity to advance the field of astrobiology.
Gale crater is the site of an ancient lake on Mars. The rover has drilled samples from mudstone rocks 3.5 billion years old found in the Yellowknife Bay formation of the crater.
The mudstone is formed when clay-like sediment (having been weathered by physical and chemical processes) settles at the bottom of a lake and is buried. This material included organic carbon, which was incorporated into mudstones.
There were numerous other conditions conducive to life at Gale crater, including chemical energy sources, low acidity, and essential nutrients for life, such as oxygen, nitrogen, and sulfur.
“Basically, this location would have offered a habitable environment for life, if it ever was present,” revealed Stern, lead author of the paper.
In order to make the measurement, Curiosity delivered the powdered rock to its Sample Analysis at Mars (SAM) instrument, which heated it to increasing temperatures in an oven.
To measure the amount of organic carbon in rocks, we convert the organic carbon to carbon dioxide (CO2) using oxygen and heat.
By adding oxygen and heat to carbon molecules, the carbon molecules can break apart, react with oxygen, and produce CO2.
The oven decomposes minerals and releases carbon embedded in them so that it can turn into CO2 by heating the sample to very high temperatures.
Despite being conducted in 2014, it took numerous years of analysis to understand the data and put the results in context with other discoveries made by the mission at Gale Crater.
During Curiosity’s decade on Mars, only one such resource-intensive experiment was conducted.
Additionally, SAM was able to analyze the carbon isotope ratios, which are helpful in identifying the carbon’s source. An isotope is a version of an element with slightly different masses due to the presence of an additional neutron at the nucleus of the atom.
Neutron count differs between Carbon-12 and Carbon-13 based on the weight of the atom. The carbon from life contains a much higher proportion of Carbon-12 because heavier isotopes react more slowly than lighter isotopes.
“in this case, the isotopic composition can really only tell us what portion of the total carbon is organic carbon and what portion is mineral carbon,” explained Stern.
“While biology cannot be completely ruled out, isotopes cannot really be used to support a biological origin for this carbon, either, because the range overlaps with igneous (volcanic) carbon and meteoritic organic material, which are most likely to be the source of this organic carbon.”
The research was published in the Proceedings of the National Academy of Sciences.
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