astroengine writes: A gas strongly associated with life on Earth has been detected again in the Martian atmosphere, opening a new chapter in a decade-old mystery about the on-again, off-again appearance of methane on Mars. The latest discovery comes from NASA's Curiosity rover, which in addition to analyzing rocks and soil samples, is sniffing the air at its Gale Crater landing site. A year ago, scientists reported that Curiosity had come up empty-handed after an eight-month search for methane in the atmosphere, leaving earlier detections by ground-based telescopes and Mars-orbiting spacecraft an unexplained anomaly. "We thought we had closed the book on methane. It was disappointing to a lot of people that there wasn't significant methane on Mars, but that's where we were," Curiosity scientist Christopher Webster with NASA's Jet Propulsion Laboratory in Pasadena, Calif., told Discovery News.