But it may not explain the presence of the gas on the Red Planet today.Traces of serpentine found at Nili Fossae on Mars.NASA/JPL/University of Arizona Surprises keep coming from Nili Fossae, a long, deep scar in the surface of Mars. In December last year, scientists reported evidence there for carbonates — minerals that typically form in the presence of water1. Then, in January, reports came that there was a large plume of methane in the area. On Earth the gas is made mostly by animals as a by-product — although it can also be produced naturally in the absence of...