Martian meteorite found in Antarctica in 1984 has revealed its nitrogen-bearing organic molecules to scientists. The research team includes research scientist Atsuko Kobayashi from the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology, Japan and research scientist Mizuho Koike from the Institute of Space and Astronautical Science at Japan Aerospace Exploration Agency (JAXA). This discovery proposes a wet and organic-rich early Mars, as carbonate minerals typically precipitate from the groundwater, which would signify habitable and favourable conditions for life to begin.
Meteorites are formed by meteor impacts which cause chunks of the surface to be blasted off to space, which eventually ends up on Earth as meteorites. The Martian meteorite Allan Hills (ALH) 84001, named for the region in Antarctica it was found in 1984, is of particular interest. It contains orange-coloured carbonate minerals, which precipitated from salty liquid water on Mars’ near-surface 4 billion years ago. These minerals provide clues to Mars’ early aqueous environment.
Contamination of the organic materials in the meteorite by antarctic ice and snow had made previous analyses unable to differentiate the extraterrestrial from the terrestrial. Also, the limitations of technology prevented the analysis of nitrogen content in the carbonates.
The research team developed new sample preparation techniques to avoid terrestrial contamination. They collected the tiny carbonate grains from the meteorite using silver tape in a clean ELSI lab. Using scanning electron microscope focused ion beam instrument at JAXA, they removed the possible surface contaminants. The nitrogen content and its chemical composition were detected using Nitrogen K-edge micro X-ray Absorption Near-Edge Structure (µ-XANES) spectroscopy. Control samples from nearby igneous minerals gave no detectable nitrogen, showing the organic molecules were only in the carbonate.
The carbonates were detected to be Martian. Nitrates, one of the strong oxidants on present Mars, was in trace amounts in the sample. This proposes that early Mars was less oxidizing than it is today.
Mars’ current conditions are too harsh for most organic molecules to survive. However, scientists have proposed that organic compounds could be preserved in near-surface settings for billions of years. The 4 billion-year-old ALH84001 provides such a setting for the samples uncovered.
Although the organic compounds have been uncovered, the origin of these compounds are up to debate. Kobayashi explains, ‘There are two main possibilities: either they came from outside Mars, or they formed on Mars. Early in the Solar System’s history, Mars was likely showered with significant amounts of organic matter, for example from carbon-rich meteorites, comets and dust particles. Some of them may have dissolved in the brine and been trapped inside the carbonates.’ The research team lead, Koike adds that alternatively, chemical reactions on early Mars may have produced the N-bearing organics on-site. Either way, they say, these findings show there was organic nitrogen on Mars before it became the red planet we know today; early Mars may have been more ‘Earth-like’, less oxidising, wetter, and organic-rich. Perhaps it was ‘blue.’
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