Mars rover detects carbon signature that hints at past life source
Excerpt: Since 2012, NASA’s Curiosity rover has trundled across Mars, drilling into rocks and running the grit through a sophisticated onboard chemistry lab, aiming to tease out evidence for life. Today, a team of rover scientists announced an intriguing signal, one that may or may not be evidence of past life, but is, at the very least, surprisingly weird. The team found that the carbon trapped in a handful of rocks probed by the rover is dramatically enriched in light isotopes of carbon. On Earth, the signal would be seen as strong evidence for ancient microbial life. Given that this is Mars, however, the researchers are reluctant to make any grand claims, and they have worked hard to concoct alternative, nonbiological explanations involving ultraviolet (UV) light and stardust. But those alternatives are at least as far-fetched as a scenario in which subterranean microbes emitted the enriched carbon as methane gas. The team concludes the study does “inch up the plausibility” that microbes once existed on the planet—and could still today, says Christopher House, a biogeochemist at Pennsylvania State University, University Park, and lead author of the study, which was published todayin the Proceedings of the National Academy of Sciences.…