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A long time in the making
Curiosity landed in Gale Crater on August 6, 2012. More than 12 years later, the rover has driven over 21 miles (34 kilometers) to ascend Mount Sharp, which is within the crater. The feature’s many layers preserve millions of years of geological history on Mars, showing how it shifted from a wet to a dry environment.
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Perhaps one of the most valuable samples Curiosity has gathered on its mission to understand whether Mars was ever habitable was collected in May 2013.
The rover drilled the Cumberland sample from an area within a crater called Yellowknife Bay, which resembled an ancient lake bed. The rocks from Yellowknife Bay so intrigued Curiosity’s science team that it had the rover drive in the opposite direction to collect samples from the area before heading to Mount Sharp.
Since collecting the Cumberland sample, Curiosity has used SAM to study it in a variety of ways, revealing that Yellowknife Bay was once the site of an ancient lake where clay minerals formed in water. The mudstone created an environment that could concentrate and preserve organic molecules and trapped them inside the fine grains of the sedimentary rock.
Freissinet helped lead a research team in 2015 that was able to identify organic molecules within the Cumberland sample.
The instrument detected an abundance of sulfur, which can be used to preserve organic molecules; nitrates, which are essential for plant and animal health on Earth; and methane composed of a type of carbon associated with biological processes on Earth.
“There is evidence that liquid water existed in Gale Crater for millions of years and probably much longer, which means there was enough time for life-forming chemistry to happen in these crater-lake environments on Mars,” said study coauthor Daniel Glavin, senior scientist for sample return at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement.
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Curiosity rover makes ‘arguably the most exciting organic detection to date on Mars’
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The NASA Curiosity rover has detected the largest organic molecules found to date on Mars, opening a window into the red planet’s past. The newly detected compounds suggest complex organic chemistry may have occurred in the planet’s past — the kind necessary for the origin of life, according to new research.
The organic compounds, which include decane, undecane and dodecane, came to light after the rover analyzed a pulverized 3.7 billion-year-old rock sample using its onboard mini lab called SAM, short for Sample Analysis at Mars.
Scientists believe the long chains of molecules could be fragments of fatty acids, which are organic molecules that are chemical building blocks of life on Earth and help form cell membranes. But such compounds can also be formed without the presence of life, created when water interacts with minerals in hydrothermal vents.
The molecules cannot currently be confirmed as evidence of past life on the red planet, but they add to the growing list of compounds that robotic explorers have discovered on Mars in recent years. A study detailing the findings was published Monday in the journal Proceedings of the National Academy of Sciences.
The detection of the fragile molecules also encourages astrobiologists that if any biosignatures, or past signs of life, ever existed on Mars, they are likely still detectable despite the harsh solar radiation that has bombarded the planet for tens of millions of years.
“Ancient life, if it happened on Mars, it would have released some complex and fragile molecules,” said lead study author Dr. Caroline Freissinet, research scientist at the French National Centre for Scientific Research in the Laboratory for Atmospheres, Observations, and Space in Guyancourt, France. “And because now we know that Mars can preserve these complex and fragile molecules, it means that we could detect ancient life on Mars.”
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While the Cumberland sample may contain longer chains of fatty acids, SAM is not designed to detect them. But SAM’s ability to spot these larger molecules suggests it could detect similar chemical signatures of past life on Mars if they’re present, Williams said.
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“Curiosity is not a life detection mission,” Freissinet said. “Curiosity is a habitability detection mission to know if all the conditions were right … for life to evolve. Having these results, it’s really at the edge of the capabilities of Curiosity, and it’s even maybe better than what we had expected from this mission.”
Before sending missions to Mars, scientists didn’t think organic molecules would be found on the red planet because of the intensity of radiation Mars has long endured, Glavin said.
Curiosity won’t return to Yellowknife Bay during its mission, but there are still pristine pieces of the Cumberland sample aboard. Next, the team wants to design a new experiment to see what it can detect. If the team can identify similar long-chain molecules, it would mark another step forward that might help researchers determine their origins, Freissinet said.
“That’s the most precious sample we have on board … waiting for us to run the perfect experiment on it,” she said. “It holds secrets, and we need to decipher the secrets.”
Briony Horgan, coinvestigator on the Perseverance rover mission and professor of planetary science at Purdue University in West Lafayette, Indiana, called the detection “a big win for the whole team.” Horgan was not involved the study.
“This detection really confirms our hopes that sediments laid down in ancient watery environments on Mars could preserve a treasure trove of organic molecules that can tell us about everything from prebiotic processes and pathways for the origin of life, to potential biosignatures from ancient organisms,” Horgan said.
Dr. Ben K.D. Pearce, assistant professor in Purdue’s department of Earth, atmospheric, and planetary sciences and leader of the Laboratory for Origins and Astrobiology Research, called the findings “arguably the most exciting organic detection to date on Mars.” Pearce did not participate in the research.

