A NASA rover has detected a bonanza of organic compounds on the surface of Mars and seasonal fluctuations of atmospheric methane in findings released Thursday that mark some of the strongest evidence ever that Earth's neighbor may have harbored life.
But National Aeronautics and Space Administration scientists emphasized there could be non-biological explanations for both discoveries made by the Curiosity rover at a site called Gale Crater, leaving the issue of Martian life a tantalizing but unanswered question.
Three different types of organic molecules were discovered when the rover dug just 2 inches (5 cm) into roughly 3.5 billion-year-old mudstone, a fine-grained sedimentary rock, at Gale Crater, apparently the site of a large lake when ancient Mars was warmer and wetter than the desolate planet it is today.
Curiosity also measured an unexpectedly large seasonal cycle in the low levels of atmospheric methane. About 95 percent of the methane in Earth's atmosphere is produced from biological activity, though the scientists said it is too soon to know if the Martian methane also is related to life.
Organic molecules are the building blocks of life, though they can also be produced by chemical reactions unrelated to life. The scientists said it is premature to know whether or not the compounds were created in biological processes.
Whether anywhere other than Earth has harbored life, perhaps even in microbial form, is one of the paramount questions in science.
"There are three possible sources for the organic material," said astrobiologist Jennifer Eigenbrode of NASA's Goddard Space Flight Center in Maryland. "The first one would be life, which we don't know about. The second would be meteorites. And the last one is geological processes, meaning the rock-forming processes themselves."