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According to a new study published in the journal, the four billion-year-old carbonates in a Martian meteorite called Allan Hills (ALH) 84001 contain organic nitrogen-containing molecules. Nature’s Communications.
A fragment of the ALH 84001 meteorite. The total size is 1.5 cm. Image credit: Koike. et al, doi: 10.1038 / s41467-020-15931-4.
Questions about life on Mars have fueled intensive studies of the planet for decades, including focused research on possible organic molecules.
NASA’s Curiosity rover reported on various organic materials, including the sulfur and chlorine-containing hydrocarbons from the 3.5 billion-year-old shales in Gale crater. Chlorine-containing methane was also found in an earlier exploration by NASA’s Viking landers, which was considered of Martian origin.
These previous investigations suggested the existence of organic matter in the near-surface system on Mars. However, little is known about the origin, distribution, preservation, and evolution of such organic compounds, as well as their possible relationship to Martian biological activity.
Along with robotic exploration, complementary knowledge has been gained from detailed geochemical investigations of Martian meteorites.
“One particular meteorite, ALH 84001, named after the Antarctic region found in 1984, is especially important,” said Dr. Mizuho Koike of the JAXA Institute for Space Science and Astronautics, and Dr. Atsuko Kobayashi of the Tokyo Institute of Technology. and Caltech and colleagues.
“It contains orange-colored carbonate minerals, which precipitated from salty liquid water on the surface near Mars 4 billion years ago.”
“As these minerals record the early aqueous environment of Mars, many studies have sought to understand their unique chemistry and whether they could provide evidence of ancient life on Mars.”
“However, previous analyzes suffered contamination with terrestrial material from Antarctic snow and ice, making it difficult to say how much organic material in the meteorite was truly Martian.”
Orange carbonate grains in the ALH 84001 meteorite. Image credit: Koike. et al, doi: 10.1038 / s41467-020-15931-4.
In the study, the researchers analyzed several carbonate grains detached from an ALH 84001 fragment.
“We use state-of-the-art analytical techniques to study the nitrogen content of ALH 84001 carbonates and find the first strong evidence for 4 billion-year-old Martian organic compounds that contain nitrogen,” the authors explained.
“After careful contamination checks, we determined that the detected organics were probably truly Martian,” they added.
“We also determined that the contribution of nitrogen in the form of nitrate, one of the strong oxidants on Mars today, was negligible, suggesting that early Mars probably did not contain strong oxidants and was less oxidizing.”
Nitrogen-containing organic matter was either synthesized locally or delivered meteorologically on early Mars. The first case requires an abiotic reduction of N (eg, N2, NOTX→ NH3) to initiate chemical reactions related to ammonia. The latter case is also possible if adequate amounts of nitrogen-containing components were supplied. This organic matter survived in fluids from the (nearby) Martian surface for 4 billion years and became trapped in ALH carbonates during precipitation. Carbonates resided in the underground system, preserving organic components for long geological periods. Image credit: Koike. et al, doi: 10.1038 / s41467-020-15931-4.
“There are two main possibilities: either organic nitrogen-containing molecules come from outside Mars, or they were formed on Mars,” said Dr. Kobayashi.
“Early in the history of the Solar System, Mars probably received a large amount of organic matter, for example from meteorites, comets, and carbon-rich dust particles. Some of them may have dissolved in the brine and become trapped inside carbonates. “
“Alternatively, chemical reactions on early Mars may have produced the nitrogen-containing organics at the site,” said Dr. Koike.
“Either way, these findings show that there was organic nitrogen on Mars before it became the Red Planet we know today.”
“The earliest Mars may have been more Earth-like, less oxidizing, wetter, and rich in organic matter. Maybe it was “blue”.
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M. Koike et al. 2020. In the place preservation of nitrogenous organic compounds in Martian carbonates from Noach. Nat Commun 11 of 1988; doi: 10.1038 / s41467-020-15931-4
