Just as researchers were once again getting their hopes up, a new study undercuts the prospects for martian life. Scientists have discovered that methane in the martian atmosphere, one of the primary signals that biological processes may be at work today on the red planet, is behaving in unexplainable ways. The results challenge the latest evidence suggesting that Mars is--or was ever--inhabited.
Mars has been a roller coaster for astrobiologists. In 1996, for example, researchers reported that a martian meteorite found in Antarctica contained traces of microbial fossils. But subsequent research discredited the idea. More recently, the U.S. National Aeronautics and Space Administration's (NASA's) two rovers and the Mars Reconnaissance Orbiter have found plentiful evidence that liquid water once flowed on the planet's surface. But none of those discoveries has led to undisputed proof that living organisms swam in Martian pools.
The latest buzz about possible Martian life started last January when a 5-year study confirmed the existence of methane in the martian atmosphere. Methane is the strongest sign yet that biology is at work on our planetary neighbor, because it is produced almost exclusively by living organisms.
But the way the methane is distributed in the martian atmosphere argues against a biological origin, researchers report tomorrow in Nature. The methane is concentrated in a single part of the atmosphere (see picture). The problem, say chemists Franck Lefàvre and François Forget, both of the Universitaire Pierre et Marie Curie in Paris, is that whether or not life is responsible for the emissions--and even if martian organisms were located only in one area of the planet--the methane should have spread much more uniformly through the atmosphere by now. The fact that it hasn't, the researchers say, argues for some sort of chemical reaction in the atmosphere that is destroying the gas before it can spread. And any reaction that destroys methane would also destroy life because the gas is made from the same types of molecules that make up life as we know it.
There's no doubt "that something is rapidly destroying the methane in the martian atmosphere," says planetary scientist Michael Mischna of NASA's Jet Propulsion Laboratory in Pasadena, California. Whatever is responsible, he says, "there's no way life could survive at or near the surface if [methane] destruction occurred so quickly."
Planetary scientist Itay Halevy, of Harvard University in Cambridge, Massachusetts, agrees. The rapid destruction of methane on Mars is a "disturbing" discovery, he says.