Last year, we reported on the discovery of an intriguing arrow-shaped rock on Mars by NASA's Perseverance rover. The rock contained chemical signatures and structures that could have been formed by ancient microbial life. Granted, this was not slam-dunk evidence of past life on Mars, and the results were preliminary, awaiting peer review. But it was an intriguing possibility nonetheless.
Now further analysis and peer review are complete, and there is a new paper, published in the journal Nature, reporting on the findings. It's still not definitive proof that there was water-based life on Mars billions of years ago, but the results are consistent with a biosignature. It's just that other non-biological processes would also be consistent with the data, so definitive proof might require analysis of the Martian samples back on Earth. You can watch NASA's livestream briefing here.
"We have improved our understanding of the geological context of the discovery since [last year], and in the paper, we explore abiotic and biological pathways to the formation of the features that we observe," co-author Joel Hurowitz, an astrobiologist at Stony Brook University in New York, told Ars. "My hope is that this discovery motivates a whole bunch of new research in laboratory and analog field settings on Earth to try to understand what conditions might give rise to the textures and mineral assemblages we've observed. This type of follow on work is exactly what is needed to explore the various biological and abiotic pathways to the formation of the features that we are calling potential biosignatures."
On February 18, 2021, Perseverance landed in Jezero Crater, a site chosen because rocks resembling a river delta are draped over its rim, indicating that flowing water might have met a lake here in the past. The little rover has multiple cameras for both general imagery and spectral analysis, supplemented by an X-ray instrument. A ground-penetrating radar instrument can reveal layering hidden below the surface; a weather module tracks atmospheric conditions and airborne dust; and a drill on the end of its robotic arm grinds clean spots for analysis. The drill can also core out small cylindrical rock samples.