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For nearly six years on the surface of Mars, NASA's Curiosity rover has detected organic molecules that offer a taste of what an ancient, near-life red planet might have looked like. Now, the rover has put together a real treat.
The discovery of a wide variety of organic molecules and the detection of a seasonal methane profile – described in two separate studies in the journal Science – add new impetus to the search for past life on Mars, according to the scientists.
"These two finds are breakthroughs in astrobiology," wrote Inge Loes ten Kate of the University of Utrecht, who has not participated in any of the studies, in a commentary on the article. .
Since the two Viking twin landing gear landed in 1976, scientists have been looking for signs of organic molecules on Mars. At most basic, organic molecules are those made of carbon and hydrogen atoms, although they can also have other atoms (such as oxygen or sulfur ). They can come from living, non-living sources, but because many are needed and produced by life on Earth, they are considered as potential biosignatures – signs of the presence of life.
Curiosity, which explores the crater of Gale since its landing in 2012, has already unearthed signs of organic molecules in the old lake bed by taking samples of rocks and subjecting them as a result of instrumentalities. laboratory in his belly. The problem was that these organic molecules contained an unusual atom: chlorine.
"The thing about chlorinated molecules, is that it is not what we usually find in natural samples, and we were not sure of the meaning at that time. Era, "said Jennifer Eigenbrode of NASA's Goddard Space Flight Center. author of one of the papers. "However, it gave us a lot of motivation to keep looking."
The rover was driven to drive about four miles to the base of Mount Sharp, the 3-mile-high mound in the middle of Gale Crater whose sediment layers serve as individual chapters in the geological history of Mars. Samples were collected at two locations, in the Mojave and Confidence Hills, and submitted as a result of the Curiosity Mars sample analysis instruments.
For the previous mudstone samples that produced the chlorinated molecules, the scientists had heated the powdered rock to 200 degrees Celsius. But for this sample, Eigenbrode and his colleagues analyzed only the gases that were released above 400 degrees Celsius.
At this temperature, "they can be certain that these gases are not the result of a leak of reagent or a reaction with perchlorate," writes Kate Kate.
The results revealed a wealth of organic compounds, Eigenbrode said – including some with carbon-bonded ring structures, such as benzenes, and others that include carbon chains, such as propane.
"Because we see these coming out of the sample at high temperatures, what they really tell us is that they're part of something bigger, a macromolecule, "she said.
Such a macromolecule could potentially look like kerogen, said Eigenbrode – a substance found in coal and black shale and meteorites. On Earth, it is often the result of an old plant or a microbial material.
These organic molecules managed to survive in the rock about 3.5 billion years ago, and this could have been a few inches from the surface for perhaps 100,000 years, said Eigenbrode.
This may be because many compounds, such as thiophene, methanethiol and dimethylsulfide, have sulfur atoms in their molecular structure. This would strengthen the relatively fragile organic molecules, allowing them to survive the radiation that has been bombarding the surface of the planet for so long.
"There were a lot of people who thought we would not find all the organic molecules we did," Eigenbrode said. With this new set of molecules, "we can now begin to understand a little bit more about how this material is preserved and where we could look for more."
The second article, led by Christopher Webster of the Jet Propulsion Laboratory at Canada Flintridge, California, marks a major step towards solving the mystery of methane on Mars.
Methane is one of the major organic molecules on Earth that is largely produced by living things, and can also be consumed by them, and thus could theoretically signal the possibility or presence of life. But methane can also be produced by normal geological processes.
The first step in determining whether a methane signal is biological is to determine where it comes from. On Mars, it was an exasperating challenge: although scientists detected bursts of methane on the planet, they appeared at random – making it difficult to determine the source.
Now, with years of atmospheric Curiosity readings at their disposal, Webster and his colleagues analyzed 55 months of Earth (about three Martian years) of data, finding that there were low levels of background radiation – and that it seemed its climax towards the end of summer in the northern hemisphere (and the end of winter in the south).
This seasonal trend seems to imply that temperature changes could trigger seasonal release, according to scientists, suggesting that methane could be stored in water-based crystals called clathrates.
"It's a huge change, completely unexpected," Webster said. "And what that does is give us the key to unlock the mysteries associated with methane, because now we have something to test our models and our understanding against."
The source of this methane, however, remains a mystery, he said.
"We do not know if this methane is old, we do not know it's modern – it could be either," Webster said. "We also do not know whether this methane was created from rock-water chemistry like serpentinization or whether it was created by methanogenic microbes – we can not distinguish it."
Neither newspaper can tell if past life has existed on Mars, according to scientists. But they provide new clues that could help researchers break through this astrobiological mystery.
"The question of whether life may have originated or existed on Mars is much more timely now that we know that organic molecules were present on its surface at that time," writes Kate Kate.
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