Big methane discovery on Mars: There isn't any methane. (+video)
NASA's Mars rover Curiosity has detected no trace of methane, contradicting earlier observations that suggest that the organic molecule might be present on the Red Planet.
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This new measurement is about six times lower than previous estimates of methane levels on Mars. Webster and his colleagues suggest this severely limits the odds of methane production by microbes below the surface of Mars or from rock chemistry.Skip to next paragraph
In Pictures Exploring Mars with Curiosity
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"It's an excellent piece of science," Muller told SPACE.com. "However, it's not to say that what is measured 1 meter (3 feet) above the ground is representative of the atmosphere in total — that's a matter of interpretation, not necessarily a matter of fact."
Is the methane hiding?
For instance, past measurements of methane in the atmosphere of Mars analyzed a region much higher above the surface, "so these might be very different measurements," Muller said. "It does leave a little wiggle room in terms of interpretation."
Moreover, when it comes to places on Earth where methane leaks out, scientists can detect large volumes of methane right at the plumes but practically none away from them, Muller said.
"It's difficult to know whether the null measurement from Curiosity has to do with being in the wrong place at the wrong time, or whether it is representative of Mars," Muller said.
"We are often asked if our measurements at Gale Crater represent the planet as a whole," Webster noted. "We remind others that the lifetime of methane on Mars is very long, about 300 years, compared to the short mixing time — months — for the whole atmosphere, so we feel our measurement does represent the global background value."
Curiosity experiment may hold the key
The Sample Analysis at Mars suite of instruments on Curiosity has yet to conduct a "methane enrichment" experiment that will increase the sensitivity of the rover's Tunable Laser Spectrometer even further — by a factor of at least 10, Webster said. "It's possible that we may then see methane at extremely low levels — or, alternatively, we will not, and our upper limit will go down much further," he added.
The ExoMars spacecraft, planned for launch in 2016, will study the chemical composition of Mars' atmosphere to learn more about any methane there.
"It can look at the vertical distribution of methane on Mars, see if it's lofted some way high up in the atmosphere or if it's near the ground," Muller said. "If it's near the ground, that's likely reflective of it seeping out of the ground; if it's high in the atmosphere, some exotic photochemical process may be responsible."
Webster stressed that Curiosity will continue its mission to assess the habitability of Mars.
"The Curiosity rover will continue to make its measurements of both atmosphere and rock samples to discover if organics other than methane exist on Mars," Webster said. "To that end, the jury is still out, as these important measurements are being made in a series of studies that will extend many months into the future. Stay tuned!"
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