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    Key of Life Ingredient on Mars | NASA’s Curiosity Rover found it for the First Time

    For the first time, scientists have used data from NASA’s Curiosity rover to measure total organic carbon, a key component in the molecules of life in Martian rocks.

    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 possibly biology, said Jennifer Stern of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. We found at least 200 to 273 parts per million organic carbon. This is comparable to, or even greater than, the amount found in rocks in places with very little life on Earth, such as parts of the Atacama Desert in South America, and more than has been detected in Martian meteorites. Organic carbon is carbon bonded to a hydrogen atom. It is the basis for organic molecules created and used by all known life forms.

    However, since organic carbon can also come from inanimate sources, its presence on Mars does not prove the existence of life there. It can come from meteorites or volcanoes, for example, or it can be formed in situ by surface reactions. Organic carbon has been found on Mars before, but previous measurements only provided information on specific compounds or represented measurements that captured only a portion of the carbon in the rock. The new measurement gives the total amount of organic carbon present in these rocks.

    Although the surface of Mars is currently inhospitable to life, there is evidence that billions of years ago the climate was more Earth-like, with a thicker atmosphere and liquid water flowing into rivers and seas. Because liquid water is, as we understand it, necessary for life, scientists believe that if life ever evolved on Mars, it could be sustained by key components such as organic carbon if it were present in sufficient abundance. Curiosity drives the field of astrobiology by investigating the habitability of Mars, studying its climate and geology.

    The rover drilled samples from 3.5-billion-year-old mudstone rocks in the Yellowknife Bay formation of Gale Crater, the site of an ancient lake on Mars. Mudstone at Gale Crater was formed as very fine sediment (by physical and chemical weathering of volcanic rock) in water that settled and buried at the bottom of a lake. Organic carbon was part of this material and was incorporated into the mudstone. In addition to liquid water and organic carbon, Gale Crater featured other conditions conducive to life, such as chemical energy sources, low acidity, and other elements essential to biology, such as oxygen, nitrogen, and sulfur. Basically, that location would have provided a habitable environment for life if it ever existed, said Stern, lead author of a paper on that research published June 27 in the Proceedings of the National Academy of Sciences.

    To make the measurement, Curiosity delivered the sample to its Sample Analysis at Mars (SAM) instrument, where a furnace heated the pulverized rock to progressively higher temperatures. This experiment used oxygen and heat to convert the organic carbon into carbon dioxide (CO2), the amount of which is measured to determine the amount of organic carbon in the rock. Adding oxygen and heat allows the carbon molecules to break apart and carbon to react with oxygen to create CO2. Some of the carbon is trapped in minerals, so the oven heats the sample to very high temperatures to break down those minerals and release the carbon to convert it into CO2. The experiment was conducted in 2014, but required years of analysis to understand the data and to place the results in the context of other discoveries from the Gale Crater missions. The resource-intensive experiment has only been conducted once during Curiosity’s 10 years on Mars.

    This process also allowed SAM to measure carbon isotope ratios, which help to understand the source of the carbon. Isotopes are versions of an element with slightly different weights (mass) due to the presence of one or more extra neutrons at the center (nucleus) of their atoms. For example, carbon-12 has six neutrons while the heavier carbon-13 has seven neutrons.

    Because heavier isotopes tend to react slightly more slowly than lighter isotopes, life’s carbon is richer in carbon-12. In this case, the isotopic composition can actually only provide information about which proportion of the total carbon is organic and which is mineral carbon, according to Stern. While the biology cannot be completely ruled out, isotopes cannot really be used to support a biological origin for this carbon either, since the range overlaps with igneous (volcanic) carbon and meteoritic organic material, which are most likely the source of this organic material are carbon.

    The research was funded by NASA’s Mars Exploration Program. The Curiosity Mars Science Laboratory mission is led by NASA’s Jet Propulsion Laboratory in Southern California.

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