Organic molecules on Mars have reached a new record of diversity, with seven never detected on the planet before. The Curiosity rover drilled the rock sample, nicknamed Mary Anning 3, in October 2020, and years of laboratory analysis have identified 21 carbon-containing molecules inside it, the most varied collection ever found on the Red Planet. Scientists have no way of knowing whether biological or geological processes made them, and either explanation remains possible. What the results do show is that ancient Mars had the chemistry to support life, and that such molecules can survive for billions of years despite radiation.
Why a clay-rich rock on Mount Sharp was the ideal place to preserve ancient organic compounds
According toNasa’s Jet Propulsion Laboratory, the sample came from a part of Mount Sharp that lakes and streams covered billions of years ago. That oasis surged and dried up several times, eventually enriching the area with clay minerals, which are especially good at preserving organic compounds. These are carbon-containing molecules that act as building blocks of life and occur throughout the solar system. The sample’s nickname honours Mary Anning, an English fossil collector and palaeontologist.
Image: Nasa
What the new nitrogen ring and sulphur-bearing molecule could mean for the chemistry behind life
One of the new discoveries is a nitrogen heterocycle, a ring of carbon atoms that contains nitrogen. Scientists consider this kind of structure a predecessor to ribonucleic acid and deoxyribonucleic acid, the nucleic acids that carry genetic information. Amy Williams of the University of Florida, lead author of the paper published in Nature Communications, said the detection is “pretty profound” because such structures can be chemical precursors to more complex nitrogen-bearing molecules. She added that nitrogen heterocycles had never been found on the Martian surface or confirmed in Martian meteorites.The other standout is benzothiophene, which contains carbon and sulphur and has turned up in many meteorites. Some scientists think those meteorites, and the organic molecules inside them, seeded prebiotic chemistry across the early solar system.
How a laboratory inside the rover’s belly turns drilled Martian rock into a list of molecules
Curiosity carries a miniature laboratory called Sample Analysis at Mars in its belly. A drill on the rover’s robotic arm pulverises a carefully chosen rock into powder and trickles it into the laboratory. There, a high-temperature oven releases gases, and instruments analyse them to reveal the rock’s composition. The laboratory can also perform wet chemistry, dropping samples into a small cup of solvent whose reactions break apart larger molecules that would otherwise be hard to detect.Only two cups hold tetramethylammonium hydroxide, a powerful solution reserved for the highest-value samples, and Mary Anning 3 was the first to be exposed to it. Curiosity has since used the second and final cup at weblike boxwork ridges formed by ancient groundwater, and the team will analyse those results for a future peer-reviewed paper.The same laboratory made last year’s discovery of the largest organic molecules found on Mars, long-chain hydrocarbons including decane, undecane and dodecane. Ashwin Vasavada, the mission’s project scientist at Nasa’s Jet Propulsion Laboratory, said it took dozens of scientists and engineers to locate the site, drill the sample and make these discoveries.
How a meteorite older than four billion years showed where the Martian molecules could come from
To check how the solvent reacts with material from beyond Earth, the paper’s authors tested the technique on a piece of the Murchison meteorite, one of the most studied meteorites of all time. It is more than four billion years old and contains organic molecules seeded throughout the early solar system. Once exposed to the solvent, the sample broke much larger molecules into some of those seen in Mary Anning 3, including benzothiophene. That shows the Martian molecules could have formed from the breakdown of even more complex compounds relevant to life.
How the discovery prepares the next instruments bound for Mars and Saturn’s moon Titan
Sample Analysis at Mars was built by Nasa’s Goddard Space Flight Centre in Greenbelt, Maryland, and is based on larger commercial-grade laboratory instruments. Engineers had to shrink it dramatically and make it run on less power. Scientists also learned to heat its oven more slowly, over longer periods, to carry out some of the experiments.Charles Malespin, the instrument’s principal investigator at Nasa Goddard and a coauthor of the study, said that working out how to do this chemistry on Mars for the first time was a feat. He added that the team is now prepared to run similar experiments on future missions.Nasa Goddard has supplied several components, including the mass spectrometer, for the Mars Organic Molecular Analyser, a next-generation version heading to the European Space Agency’s Rosalind Franklin Mars rover. A similar instrument, the Dragonfly Mass Spectrometer, will explore Saturn’s moon Titan aboard Nasa’s Dragonfly rotorcraft. Both can perform wet chemistry with the same solvent.