Non-biological Organic Carbon Found to Originate on Mars

Molecules containing carbon and hydrogen – the building blocks of all life on Earth – have been the targets of missions to Mars from Viking to the present day. While these molecules have previously been noticed in meteorites from Mars, scientists have disagreed about how this organic carbon was formed and whether or not it came from Mars.

Theories about their origin include contamination from Earth or other meteorites, the results of chemical reactions on Mars, or that they are the remnants of ancient Martian biological life.

A new paper published May 24 in Science Express by Carnegie’s Andrew Steele and a consortium of scientists that includes Planetary Science Institute’s Marc Fries provides strong evidence that this carbon did, indeed, originate on Mars, although it is not of biological origin. These findings give researchers insight into the chemical processes taking place on Mars and will help aid future quests for evidence of ancient or modern Martian life

Steele’s team examined samples from 11 Martian meteorites whose ages span about 4.2 billion years of Martian history. They detected large carbon compounds in 10 of them. The molecules were found inside of grains of crystallized minerals. Since these molecules were found in Martian meteorites of such an extraordinary span of ages, their presence means that Mars has been making its own organic compounds throughout its history and apparently continues to do so today.

“We knew these organic compounds were in the Martian meteorites, but until we performed this study no one knew exactly where they were in the rocks or how they were formed,” said Fries, a research scientist at the Planetary Science Institute. “It was a puzzle, and now we finally have enough pieces in place to say, okay, now we understand what is going on here.”

Using an array of sophisticated research techniques, the team was able to show that at least some of the macromolecules of carbon were indigenous to the meteorites themselves and not contamination from Earth.

“What this all means is that Mars is making its own organic compounds. Previous to this, we thought that carbon compounds on Mars only fell there in meteorites, or perhaps were bound up in any life forms that might be living there. Now we know that simply finding organic compounds that aren’t from meteorites doesn’t automatically mean that they come from life,” Fries said. “While it sounds like it complicates things, it actually gives us a clearer picture of Mars and will help us build robust conclusions about whether anything is, or has been, alive there.”

In a separate paper going to press in American Mineralogist, Steele and his team studied a meteorite called Allan Hills 84001 that was reported to contain relicts of ancient biological life on Mars. The paper demonstrated that these supposed remnants could have been created by chemical reactions involving the graphite form of carbon, rather than biological processes. Both of these papers reveal a pool of reduced carbon on Mars and will help scientist involved in future Mars missions distinguish these non-biologically formed molecules from potential life.

The research for the Science Express paper was funded by NASA Astrobiology, Mars and Cosmochemistry programs, the W.M. Keck Foundation, the Natural Science and Engineering Research Council of Canada, and the Carnegie Institution for Science. The research for the American Mineralogist paper was supported by NASA Astrobiology, Mars and Cosmochemistry programs.

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Celebrating its 40th anniversary, the Planetary Science Institute is a private, nonprofit 501(c)(3) corporation dedicated to solar system exploration. It is headquartered in Tucson, Arizona, where it was founded in 1972.

PSI scientists are involved in numerous NASA and international missions, the study of Mars and other planets, the Moon, asteroids, comets, interplanetary dust, impact physics, the origin of the solar system, extra-solar planet formation, dynamics, the rise of life, and other areas of research. They conduct fieldwork in North America, Australia and Africa. They also are actively involved in science education and public outreach through school programs, children’s books, popular science books and art.

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