天文学：火星での生命探査に課題あり

Scientific instruments currently deployed on Mars may lack the sensitivity to identify possible traces of life in this environment, suggests a Nature Communications paper.

Since the Viking missions in the 1970s, there have been multiple attempts to search for signs of life on Mars. Now, half a century later, even the most recent, highly sophisticated instruments of NASA’s Curiosity and Perseverance rovers have only identified low levels of simple organic molecules. These results raise questions about whether our ability to detect evidence of life is hindered by current instrument limitations or the nature of materials within martian rocks.

Armando Azua-Bustos and colleagues tested instruments that are currently, or may be, sent to Mars alongside state-of-the-art laboratory equipment to analyse samples from Red Stone, the sedimentary fossils remains of a river delta located in the Atacama Desert, Chile. These deposits formed under highly arid conditions around 160–100 million years ago and are geologically similar to the Jezero crater on Mars currently being studied by Perseverance. Using highly sensitive laboratory-based techniques, the authors found a mixture of biosignatures of both extinct and living microorganisms. Microbial culturing and gene sequencing showed many of the DNA sequences found primarily came from an unidentifiable ‘dark microbiome’, with most of the genetic material coming from previously undescribed microorganisms. However, analyses of testbed instruments used on Mars reveal that they were barely able to detect molecular fossil signatures at the limits of detection.

The findings indicate that similarly low levels of organic matter, expected to be present if there was life on Mars billions of years ago, will be difficult if not impossible to detect with the technology currently used on Mars. The authors stress the importance of returning samples to Earth to conclusively address whether life ever existed on the red planet.