NASA's Curiosity rover discovered the most complex set of organic molecules found to date on Mars, including a chain of 12 consecutive carbon atoms, which on Earth is usually associated with a possible biological origin. The discovery was made using the Sample Analysis at Mars (SAM) instrument aboard the rover, which has been exploring Gale Crater since 2012.
An international research group coordinated by the French National Centre for Scientific Research (CNRS), including colleagues from the United States, Mexico, and Spain, identified these complex organic molecules on Mars, marking the first discovery of such molecules of this kind on the planet.
The organic molecules discovered by Curiosity were unprecedented in size, containing up to 12 consecutive carbon atoms, and were very similar to those produced by life on Earth, according to The Guardian. Specifically, the detection of long-chain linear alkane compounds, such as decane (C₁₀H₂₂), undecane (C₁₁H₂₄), and dodecane (C₁₂H₂₆), was made by the SAM instrument.
These organic molecules are structures made up of long chains of carbon atoms, making them similar to fatty acids produced by living organisms on Earth. The compounds were found within clay-rich samples dating back 3.7 billion years, collected from Yellowknife Bay, an ancient Martian lakebed that harbored all the necessary ingredients for life in Mars's warmer, wetter past.
"These molecules can be made by chemistry or biology," said Dr. Caroline Freissinet, an analytical chemist who led the research at the Atmospheres and Space Observations Laboratory in Guyancourt, near Paris, according to The Guardian. "By finding long molecules, that is to say composed of 10, 11, and even 12 consecutive carbon atoms, we say that it is a little more probable that life was present on Mars, at that place, 3.7 billion years ago," she added.
However, the researchers do not claim to have found a definitive biosignature. "The origin of these molecules remains uncertain, as they could come from abiotic or biological sources," they wrote in a study published in PNAS.
The lack of geological activity and the cold, arid climate of Mars contributed to preserving the organic matter in a clay-rich sample for the last 3.7 billion years, coinciding with the time when life appeared on Earth. This finding suggests that organic signatures of life can be preserved in Martian rock for billions of years, strengthening the hypothesis of ancient life.
"The findings reported in this paper present the best chance we have seen for identifying the remains of life on Mars," stated John Eiler, a professor of geology and geochemistry at the California Institute of Technology.
The Curiosity rover's work in Gale Crater, which has traveled more than 20 miles (32 km) since landing on Mars in 2012, has been crucial in revealing new details of the planet's ancient environment. Gale Crater is believed to have been an ancient lakebed that once harbored rivers and watery environments, making it a suitable place for life.
The discovery of these long-chain organic molecules bolsters hopes that remnants of Martian life might still be found. If there was ever life on Mars, its signature could potentially be found in the stones.
One of the goals of ESA's upcoming ExoMars mission, launching in 2028, will be to search for signs of complex, life-like chemistry on Mars, including the search for biomarkers and the use of advanced drilling technology to enhance its search for organic molecules beneath the Martian surface.
Additionally, the joint NASA-ESA Mars Sample Return mission, planned for the 2030s, will bring to Earth samples collected by the Perseverance rover, allowing for laboratory analyses that are currently impossible on Mars. Determining the implications of these findings will almost certainly require future missions.
The success of this detection reinforces the role of the Curiosity rover in exploring Martian organic chemistry and paves the way for future interplanetary science missions in search of signs of complex, life-like chemistry.
"It's the first time such complex and ancient molecules have been identified on Mars," stated Felipe Gómez Gómez, a researcher at the Center for Astrobiology (CAB/CSIC-INTA) in Spain. "We know them very well; we know what they are because here on Earth there are many examples," he added.
The researchers emphasize that while these fatty acids are a component of terrestrial cells, they can also form in abiotic processes. Scientists cannot yet determine how the molecules were formed—whether by the activity of some organism or if they are abiotic molecules, meaning their formation did not involve a living being.
According to Gómez, this finding will help understand the preservation capacity of such molecules on the Red Planet. "This finding does not mean that we have found life on Mars, but it is a step further in understanding its chemical history and its potential to have harbored organisms in the past," the authors of the study explained.
Beyond Mars, the exploration of the Solar System will continue with Dragonfly, NASA's drone that is due to explore the surface of Titan, Saturn's largest satellite, from 2034 onwards. Dragonfly will carry an instrument similar to SAM and will analyze the organic chemistry of Titan, a world rich in hydrocarbons.
The article was written with the assistance of a news analysis system.