The Curiosity rover landed on Mars on August 5, 2012, while the more recent Perseverance rover landed on Mars' Jezero Crater on February 18 last year. The Perseverance mission has recently performed several historic firsts, including the first controlled flight of a helicopter on another planet.

That's not to say Curiosity isn't still providing valuable insight into our planetary neighbor. Most recently, it has provided compelling evidence for the key ingredient of life.

"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," 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 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."

Organic carbon — carbon bound to a hydrogen atom — is the basis for organic molecules and it is used by all known life forms. While the new measurement of organic carbon on Mars doesn't prove the existence of life on the red planet, it does provide an indication that the conditions on Mars may have once been suitable for life to grow on the planet.

Investigating 3.5-billion-year-old rocks on Mars

The Curiosity rover drilled its samples from 3.5-billion-year-old mudstone rocks in the Yellowknife Bay formation of Gale crater, the site of an ancient lakebed on Mars. The rover then delivered the sample to its Sample Analysis at Mars (SAM) instrument, where an oven heated the powdered rock to progressively higher temperatures to take the measurements. The organic carbon was converted to carbon dioxide to measure the amount of organic carbon in the rocks.

Though the researchers say the new findings provide valuable data, they also the highlight the fact that it does not provide conclusive evidence of life on Mars. "While biology cannot be completely ruled out," Stern said, "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 new information will be analyzed alongside other recent findings, including the Perseverance rover's photographic evidence showing that the Jezero crater was once a large lake with a flowing river attached. Perseverance and Curiosity will continue to investigate the surface of the red planet by collecting samples. Some of these will eventually make their way back to Earth as part of the Mars Sample Return mission expected to take place in the 2030s.

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https://interestingengineering.com/nasa-ancient-microbial-life-mars