Methane Mystery at Mars

The NASA Mars Curiosity science team revealed today that the rover’s instruments detected an unexplained spike in atmospheric methane concentrations about this time last year.  One source — but not the only source — of methane is biological activity.

The amount and source of methane on Mars is of great interest to scientists not only because it is a possible signature of life, but because of conflicting readings over the years.  For example, in September 2013, a year after Curiosity landed, NASA announced that the rover had not detected significant amounts of methane, a surprise because during the previous decade, Earth-based telescopes and instruments on spacecraft orbiting Mars had detected the gas. 

Today’s announcement at the fall meeting of the American Geophysical Union (AGU) in San Francisco is that in late 2013 and early 2014, the rover detected a 10-fold spike in methane concentrations in the atmosphere near the rover.  Four measurements during that period averaged 7 parts per billion (ppb), compared to readings before and after, which were one-tenth of that.

The presence of methane is not a sure sign of either past or present life, but opens that possibility.  Sushiel Atreya of the University of Michigan and a member of the Curiosity science team said today that “this temporary increase in methane – sharply up and then back down – tells us there must be some relatively localized source. … There are many possible sources, biological or non-biological, such as interaction of water and rock.”

NASA’s carefully worded press release also said that Curiosity detected organic chemicals in powder drilled from a rock, “the first definitive detection of organics in surface materials on Mars.”  However, the statement goes on to say these “Martian organics could either have formed on Mars or been delivered to Mars by meteorites” and organic molecules “are chemical building blocks of life, although they can exist without the presence of life.”

Curiosity’s mission is not to determine if there is life on Mars, but whether or not the planet could have supported life — its “habitability.”  Determining if life exists elsewhere than on Earth is one of NASA’s major science objectives.  Mars has fascinated people as a possible site for extraterrestrial life at least since 1877 when the Italian astronomer Giovanni Schiaparelli reported that he had observed “canali” on the surface and some interpreted that as meaning canals created by intelligent beings rather than naturally occurring channels.  The belief that intelligent beings once lived on Mars persists to this day despite the extensive research conducted there by spacecraft orbiting the planet and roving on its surface. 

Separate from the debate over intelligent life, some scientists think microbial life may once have existed there, or perhaps still does today in subsurface permafrost, for example.  Today’s announcement makes no definitive determination about that question, but adds to the mystery of the source of the methane on the planet.

Detecting methane in the Martian atmosphere is one of the objectives of India’s Mars Orbiting Mission (MOM), which reached the planet in September.  Europe’s Mars Express orbiter also can detect methane and, in fact, it was observations from that spacecraft a decade ago that raised expectations that methane was much more abundant than Curiosity initially measured.