New, NASA-funded research indicates that very large molecules containing carbon - a key ingredient for the building blocks of life - have originated on Mars.
Through a study of Mars meteorites that have landed on Earth, the Carnegie Institution for Science team's established that the reduced carbon - carbon that's bonded to hydrogen or itself - found inside isn't a result of contamination. But, says the team, it comes from volcanic processes, not life.
The macromolecules themselves of biological origin, but do show that complex carbon chemistry has taken place on Mars.
"These findings show that the storage of reduced carbon molecules on Mars occurred throughout the planet's history and might have been similar to processes that occurred on the ancient Earth," says Carnegie's Andrew Steele.
"Understanding the genesis of these non-biological, carbon-containing macromolecules on Mars is crucial for developing future missions to detect evidence of life on our neighboring planet."
The team examined samples from 11 Martian meteorites from a period spanning about 4.2 billion years of Martian history, and detected large carbon compounds in ten of them, inside grains of crystallized minerals.
And they were able to show that at least some of the macromolecules of carbon were indigenous to the meteorites themselves and not contamination from Earth.
The team next looked at the carbon molecules in relation to other minerals in the meteorites to see what kinds of chemical processing these samples endured before arriving on Earth. Their findings indicate that the carbon was created by volcanic activity on Mars, and show that Mars has been doing organic chemistry for most of its history.
Molecules containing large chains of carbon and hydrogen have been found previously in Mars meteorites, but scientists have disagreed about how the carbon in them was formed and whether it even came from Mars - a debate settled by the new findings.
"Although this study has not yielded evidence that Mars has or once may have supported life, it does address some important questions about the sources of organic carbon on Mars," says Mary Voytek, director of NASA's Astrobiology Program.
"With the Curiosity rover scheduled to land in August, these new research results may help Mars Science Laboratory scientists fine-tune their investigations on the surface of the planet by understanding where organic carbon may be found and how it is preserved."
The findings should help scientists involved in Mars missions distinguish non-biologically formed carbon molecules from potential life.