NASA’s Curiosity rover uses its Mast Camera or Mastcam to capture this area at the edge of a place called Yellowknife Bay. Credit: NASA / JPL-Caltech / MSSS
A newly published study quantifies the presence of organic carbon in Martian rocks.
For the first time, scientists using data from NASA’s Curiosity rover are measuring total organic carbon – a key component in the molecules of life – in Martian rocks.
“Total organic carbon is one of several measurements [or indices] which help us understand how much material is available as a raw material for prebiotic chemistry and potentially biology, ”said 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 places with very little life on Earth, such as parts of the Atacama Desert in South America, and more than was found in meteorites on Mars.
Organic carbon is carbon that is attached to a hydrogen atom. This is the basis for organic molecules that are 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. For example, it can come from meteorites, volcanoes or form on site through surface reactions. Organic carbon has been found on Mars before, but previous measurements provide information only on certain compounds or are measurements that capture only part of the carbon in the rocks. The new measurement gives the total amount of organic carbon present in these rocks.
NASA’s Curiosity rover uses its Mast Camera or Mastcam to capture this area at the edge of a place called Yellowknife Bay. The image is a combination of three mosaics made on December 24, 25 and 28, 2012 (137th, 138th and 141st Martian days, or salt, from the mission). Credit: NASA / JPL-Caltech / MSSS
Although the surface of Mars is currently inhospitable to life, there is evidence that billions of years ago the climate was more like Earth, with a denser atmosphere and liquid water flowing into rivers and seas. Because liquid water is essential for life, as we understand it, scientists believe that Martian life, if it ever evolved, could be sustained by key ingredients such as organic carbon if present in sufficient quantities.
Curiosity is advancing in the field of astrobiology, studying the habitability of Mars, studying its climate and geology. The rover samples 3.5 billion years of muddy rocks in the Yellowknife Bay formation at Gale Crater, the site of an ancient lake on Mars. The mudstone in Gale Crater formed as a very fine sediment (from the physical and chemical weathering of volcanic rocks) in water that settled to the bottom of a lake and was buried. Organic carbon was part of this material and was included in the mudstone. In addition to liquid water and organic carbon, Gale Crater has had other favorable conditions for life, such as chemical energy sources, low acidity, and other elements necessary for biology, such as oxygen, nitrogen, and sulfur. “In principle, this place would offer a habitable environment if it ever existed,” said Stern, lead author of an article on the study published June 27 in the Proceedings of the National Academy of Sciences.
The NASA Curiosity rover uses its left navigation camera to record this view of the step down in a shallow depression called Yellowknife Bay. The descent into the pool passed through a step about 2 feet high, which is visible in the upper half of this image. NASA’s Curiosity rover uses its navigation camera (Navcam) to capture this view after entering a place called Yellowknife Bay on December 12, 2012, the 125th Martian day, or salt, of the mission. Credit: NASA / JPL-Caltech
To perform the measurement, Curiosity delivered the sample to its Mars Sample Analysis Instrument (SAM), where an oven heats the powder rock to progressively higher temperatures. This experiment uses oxygen and heat to convert organic carbon into carbon dioxide (CO2), the amount of which is measured to obtain the amount of organic carbon in the rocks. The addition of oxygen and heat allows carbon molecules to break down and react with carbon with oxygen to form CO2. Some of the carbon is locked in minerals, so the oven heats the sample to very high temperatures to decompose these minerals and release the carbon to convert it into CO2. The experiment was conducted in 2014, but requires years of analysis to understand the data and place the results in the context of the mission’s other findings in Gale Crater. The resource-intensive experiment was performed only once in the 10 years on Mars of Curiosity.
This process also allowed SAM to measure the ratios of carbon isotopes that help understand the source of carbon. Isotopes are versions of an element with slightly different weights (masses) due to the presence of one or more additional neutrons in the center (nucleus) of their atoms. For example, carbon-12 has six neutrons, while heavier carbon-13 has seven neutrons. Because heavier isotopes tend to react a little slower than lighter isotopes, the carbon in life is richer in carbon-12. “In this case, the isotopic composition can really only tell us what part of the total carbon is organic carbon and what part is mineral carbon,” Stern said. “Although biology cannot be completely ruled out, isotopes cannot really be used to maintain the biological origin of this carbon, as the range overlaps with igneous (volcanic) carbon and meteorite organic material, which are most likely the source of this organic carbon. “
The study is funded by NASA’s Mars exploration program. Curiosity’s Mars Science Laboratory mission is led by NASA’s Jet Propulsion Laboratory in Southern California; The JPL is operated by Caltech. The SAM was built and tested at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Charles Malespin is the principal investigator of SAM.
Add Comment