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In a groundbreaking discovery for Mars exploration, NASA’s Curiosity rover has identified the largest organic molecules yet on the red planet. This finding opens intriguing possibilities into Martian history, suggesting complex organic chemistry, potentially crucial for the emergence of life, may have occurred in Mars’ ancient past. This research marks a significant step in the quest to understand the potential for past life on Mars and is a key focus for astrobiologists and planetary scientists globally.
Largest Organic Molecules Unearthed on Mars by Curiosity Rover
Analysis from the Curiosity rover has revealed the presence of organic compounds, including decane, undecane, and dodecane, within a pulverized 3.7 billion-year-old rock sample. The rover’s onboard laboratory, SAM (Sample Analysis at Mars), facilitated this crucial detection.
Scientists hypothesize that these extended molecular chains could be remnants of fatty acids. Fatty acids are organic molecules serving as fundamental building blocks for life on Earth and are essential in forming cell membranes. However, these compounds can also arise abiologically through water interacting with minerals in hydrothermal vents.
Currently, these molecules cannot be definitively confirmed as indicators of prior life on Mars. Yet, their discovery enhances the increasing collection of compounds previously detected on Mars by robotic missions. The detailed findings are documented in a study published in the journal Proceedings of the National Academy of Sciences on Monday.
The identification of these fragile molecules provides reassurance to astrobiologists. It suggests that if biosignatures, or indicators of past life, ever existed on Mars, they could still be detectable despite the planet’s exposure to harsh solar radiation for millions of years.
“If ancient life existed on Mars, it would likely have released delicate and intricate molecules,” stated Dr. Caroline Freissinet, the lead study author and a research scientist at the French National Centre for Scientific Research. “Our new understanding that Mars can preserve these complex, fragile molecules significantly boosts the prospect of detecting ancient life on the planet.”
This discovery also strengthens the rationale for Mars sample return missions. Such missions would enable scientists to conduct in-depth studies on Earth using advanced equipment and potentially resolve the long-standing question of whether life has ever existed beyond Earth.
Decades-Long Mission Yields Key Sample
Curiosity’s journey began with its landing in Gale Crater on August 6, 2012. Over more than a decade, the rover has traversed over 21 miles (34 kilometers), ascending Mount Sharp within the crater. This geological feature preserves a rich Martian history across millions of years, revealing the planet’s transformation from a wetter to a drier environment.
A particularly significant sample, instrumental in understanding Mars’ habitability, was collected by Curiosity in May 2013. This sample, named Cumberland, was drilled from Yellowknife Bay, an area within Gale Crater that resembled an ancient lakebed.
The Yellowknife Bay rocks profoundly interested the Curiosity science team, leading them to redirect the rover to gather additional samples from this area before proceeding towards Mount Sharp.
Since obtaining the Cumberland sample, Curiosity has employed SAM to perform diverse analyses. These investigations confirmed that Yellowknife Bay was once an ancient lake containing water where clay minerals formed. The resulting mudstone created conditions conducive to concentrating and preserving organic molecules, trapping them within the fine-grained sedimentary rock.
Dr. Freissinet was a leading member of the research team in 2015 that initially identified organic molecules in the Cumberland sample.
The earlier analyses revealed a substantial amount of sulfur, known for its preservative qualities for organic molecules, nitrates, vital nutrients for terrestrial plant and animal life, and methane with a carbon signature linked to biological processes on Earth.
“Evidence strongly suggests that liquid water persisted in Gale Crater for millions of years, possibly longer,” stated study coauthor Daniel Glavin, senior scientist for sample return at NASA’s Goddard Space Flight Center. “This extended period indicates ample time for life-generating chemistry to occur within these ancient Martian lake environments.”
Curiosity has preserved portions of the Cumberland sample in a specialized container, allowing the team to revisit it for further experimentation, even remotely. Innovative methods were developed and tested in terrestrial labs before instructions were sent to the rover to conduct new experiments on the precious sample.
In an effort to detect amino acids, the protein building blocks, the team commanded Curiosity to heat the Cumberland sample twice within SAM’s oven. While amino acids were not detected, the experiments yielded an entirely unexpected and intriguing discovery.
Intriguing Molecular Detection
The detection of trace amounts of decane, undecane, and dodecane was initially surprising to the research team. This prompted them to perform a controlled reverse experiment on Earth to confirm whether these organic compounds were indeed derived from fatty acids such as undecanoic acid, dodecanoic acid, and tridecanoic acid.
The scientists mixed undecanoic acid with Martian-like clay and heated the mixture, mimicking SAM oven conditions. The experiment successfully released decane, mirroring Curiosity’s findings.
Each fatty acid fragment identified by Curiosity contained long chains of 11 to 13 carbon atoms. Molecules previously found on Mars were smaller and less complex, possessing a lower atomic weight than these newly discovered molecules.
“It is noteworthy that non-biological processes typically generate shorter fatty acids, with fewer than 12 carbons,” commented study coauthor Dr. Amy Williams, associate professor of geology at the University of Florida. “Larger, more complex molecules are more likely to be required for the origin of life, should it have ever occurred on Mars.”
Although the Cumberland sample might contain even longer fatty acid chains, SAM’s design limits its ability to detect them. However, SAM’s successful detection of these larger molecules suggests its capability to identify similar chemical signatures of past Martian life if present, according to Williams.
“Curiosity’s primary goal isn’t life detection,” Freissinet clarified. “It is designed to assess habitability — to determine if conditions were ever suitable for life to evolve. These new results push Curiosity to the boundaries of its capabilities and potentially exceed initial mission expectations.”
Prior to Mars missions, scientists were uncertain about finding organic molecules on Mars due to the intense radiation exposure over billions of years, Glavin noted.
While Curiosity will not revisit Yellowknife Bay, pristine portions of the Cumberland sample remain onboard. The team is now focused on designing a new experiment to maximize the information gleaned from this sample. Further detection of similar long-chain molecules would represent another significant stride in determining their origins, Freissinet elaborated.
“This sample is the most valuable resource we have on board, awaiting the perfect experiment,” she emphasized. “It harbors secrets we are determined to unlock.”
Briony Horgan, a coinvestigator on the Perseverance rover mission and professor of planetary science at Purdue University, lauded the detection as “a major achievement for the entire team.” Horgan was not directly involved in this study.
“This discovery truly reinforces our hopes that sediments deposited in ancient Martian aquatic environments could preserve a wealth of organic molecules,” Horgan stated, “molecules that could reveal insights into prebiotic processes, the pathways to life’s origins, and potential biosignatures from ancient Martian organisms.”
Dr. Ben K.D. Pearce, assistant professor at Purdue University, described the findings as “arguably the most exciting organic detection to date on Mars.” Pearce was not a participant in this research.
Pearce pointed out that some scientists theorize that fatty acids like decanoic acid and dodecanoic acid formed the membranes of the earliest simple, cell-like structures on Earth.
“(This is) the closest we’ve come to detecting a significant biomolecule-related signal – potentially related to membrane structure, a fundamental characteristic of life,” Pearce explained. “Organic molecules alone are interesting but not proof of life. In contrast, biomolecules like membranes, amino acids, nucleotides, and sugars are essential biological components, and finding any would be truly groundbreaking, though we have yet to do so.”
Future Mars Sample Return Missions
The European Space Agency’s ExoMars Rosalind Franklin rover, scheduled for launch in 2028, will carry an instrument complementary to SAM, potentially enhancing our understanding of Martian organics. The rover’s LS6 instrument will be capable of drilling up to 6.5 feet (2 meters) beneath the Martian surface, potentially accessing larger and better-preserved organic molecules.
While Curiosity’s valuable samples remain on Mars, the Perseverance rover is actively gathering samples in Jezero Crater, the site of an ancient lake and river delta. These samples are intended for return to Earth in the 2030s via the ambitious Mars Sample Return program.
Both Curiosity and Perseverance have detected various organic carbon molecules across different Martian locations, suggesting that organic carbon is widespread on Mars, according to Williams.
Dr. Ashley Murphy, a postdoctoral research scientist at the Planetary Science Institute, emphasized that while Curiosity and Perseverance have proven their ability to detect organic matter, their onboard instruments cannot definitively answer all questions about their origins. Murphy, who has studied organics identified by Perseverance, was not involved in this particular research.
“To effectively address the biosignature question, these samples require advanced, high-resolution, and high-sensitivity analyses in Earth-based laboratories, which can only be achieved through sample return missions,” Murphy stated.
If the molecules within the Cumberland sample are indeed byproducts of microbial life from 3.7 billion years ago, it would align with the period scientists believe life began on Earth, Glavin noted. Curiosity’s findings bring us “so close” to potentially resolving this, yet definitive answers will likely emerge from studying samples here on Earth, he believes.
“I am increasingly optimistic that we will finally be able to resolve the long-standing debate about life on Mars,” Glavin concluded.