Love and Light.
Methane on Mars: the plot thickens
Discoveries of methane on Mars suggest it is actively being replenished but the source is a mystery (Image: ESA/DLR/FU Berlin, G Neukum)
Methane on Mars may be produced at rates 3000 times higher than previously thought and partially destroyed by dust storms, controversial new research suggests.
The work is sure to reignite the debate over a possible biological origin for the gas, but another team reports that subsurface volcanism alone - and not life - can account for the gas.
Sunlight is thought to destroy methane molecules in Mars's atmosphere over about 300 years. So recent discoveries of the gas by space- and ground-based instruments suggested it is actively being replenished by geological processes or possibly living microbes.
The mystery deepened when some researchers claimed to find methane concentrated in certain locations on Mars. That is a puzzle because atmospheric currents are expected to spread the gas evenly around the planet in a matter of weeks or months.
Now, a team led by Michael Mumma of NASA's Goddard Space Flight Center in Greenbelt, Maryland, US, reports further evidence of the phenomenon. Using an infrared telescope in Hawaii and the Gemini South telescope in Chile, the group found concentrations of methane ranging from zero to more than 250 parts per billion across Mars.
Such a drastic difference suggests something must be destroying the methane before it can be mixed uniformly through the atmosphere, says Mumma. And if it is destroyed in one month, he says, that implies it must be replenished 3000 times faster than current estimates suggest.
"There's a very significant increase required. But I think it's premature to draw conclusions [about a biological source], says Mumma, who will present the results at a planetary sciences meeting in Cambridge, UK, in September 2005.
Still, he says the research begs the question of what - besides sunlight - could be destroying the methane. Sushil Atreya of the University of Michigan in Ann Arbor, US, and colleagues may have an answer and will be presenting their work at the same meeting.
They say dust particles that collide during Martian dust storms can become charged, with smaller particles gaining electrons and rising on air currents. This creates a large electric field that can accelerate electrons until they break apart water molecules in the atmosphere. The detritus from this smash-up can then oxidise, or destroy, methane molecules.
It is not clear how large this dust-storm effect is, "but it does establish for the first time that there are other mechanisms for producing oxidants", Mumma notes.
Jim Lyons, a planetary scientist at the University of California in Los Angeles, US, agrees. "It doesn't look to me like you have enough dust activity to produce the electric fields you want to produce," he told New Scientist. "But it's probably the best idea if we really do need a mechanism for destroying methane in the atmosphere."
But he is sceptical that any methane exists on Mars - much less in different concentrations across its surface. Still, he and colleagues have just published a study showing that geological activity could explain any methane that is present.
Recent high-resolution images of Mars reveal crater-free surfaces that may have been covered by lava within the last 2 million years. That suggests magma could still be flowing below the surface today, says Lyons.
He and colleagues say magma welling up about 10 kilometres below the surface could melt any subsurface water ice and infuse it with carbon dioxide. As the water cools, it would release methane to seep upwards into the atmosphere.
He says a patch of subsurface magma just 1 km wide could account for methane at the 10 parts per billion level seen by some groups, and that a larger patch could account for Mumma's reported values.
Journal reference: Geophysical Research Letters (DOI: 10.1029/2005GL022161)
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