No methane on Mars, says Curiosity
Sen—NASA's Curiosity rover has not been able to detect any methane during its study of the Martian atmosphere.
Methane can be created by microbes and is considered a potential sign of life, though it can have non-biological sources.
The rover used its tunable laser spectrometer (part of its Sample Analysis at Mars (SAM) toolkit) to analyse samples of the Martian atmosphere six times between October last year and June. No methane was detected. Taking into account the sensitivity of the spectrometer, scientists calculate the amount of methane in the atmosphere to be no more than 1.3 parts per billion -- about one-sixth of the amount previously estimated.
Michael Meyer, NASA's lead scientist for Mars exploration, explained: "This important result will help direct our efforts to examine the possibility of life on Mars. It reduces the probability of current methane-producing Martian microbes, but this addresses only one type of microbial metabolism. As we know, there are many types of terrestrial microbes that don't generate methane."
Previous analysis of the Martian atmosphere has been based on observations from orbit around the planet and from Earth. These suggested that methane, the most abundant hydrocarbon in the Solar System, could make up to 45 parts per billion on Mars, leading to suggestions of the possibility of a biological source. Curiosity's measurements are inconsistent with such concentrations.
"It would have been exciting to find methane, but we have high confidence in our measurements, and the progress in expanding knowledge is what's really important," said Chris Webster of NASA's Jet Propulsion Laboratory and lead author of the new report. "We measured repeatedly from Martian spring to late summer, but with no detection of methane."
"There's no known way for methane to disappear quickly from the atmosphere," said one of the paper's co-authors, Sushil Atreya of the University of Michigan. "Methane is persistent. It would last for hundreds of years in the Martian atmosphere. Without a way to take it out of the atmosphere quicker, our measurements indicate there cannot be much methane being put into the atmosphere by any mechanism, whether biology, geology, or by ultraviolet degradation of organics delivered by the fall of meteorites or interplanetary dust particles."
Atreya estimated the highest concentration of methane that could be present without being detected by Curiosity's measurements so far would be no more than 10 to 20 tons per year of methane entering the Martian atmosphere -- about 50 million times less than on Earth.
Two new missions to Mars will gather more data on the atmosphere. NASA's next mission to Mars, the Mars Atmosphere and Volatile Evolution Mission (MAVEN) will study how the loss of atmosphere has affected the planet's climate. The probe is due to launch in November this year and arrive in Mars' orbit in September 2014.
The European Space Agency (ESA) and the Russian space agency Roscosmos are working towards the launch of ExoMars in 2016. ExoMars will include the Trace Gas Orbiter (TGO) to search for evidence of methane and other atmospheric gases that could be signs of active biological or geological processes.
Curiosity, more formally known as the Mars Science Laboratory, landed on Mars on August 6 (UTC). The rover is on an initial two year mission (one Martian year) to find evidence if the Red Planet ever had conditions suitable for microbial life. The rover has ten scientific instruments as its disposal. NASA's Jet Propulsion Laboratory (JPL), based in Pasadena, California, a division of the California Institute of Technology, manages the Mars Science Laboratory mission for NASA.