Planetary scientists monitoring Mars through the newly arrived Mars Express orbiter are reporting the presence of methane in the martian atmosphere. If true, either the planet is releasing methane trapped since its formation, perhaps through previously undetected volcanic eruptions or hot springs, or there is life on Mars.
The reported detection of methane is based on early observations by the Planetary Fourier Spectrometer (PFS) onboard Mars Express. The instrument is run by Vittorio Formisano of the Institute of Physics and Interplanetary Space in Rome and his team. The PFS records the infrared radiation emitted by molecules of atmospheric gas; each molecule emits at a combination of wavelengths unique to its structure.
At a press conference in Paris held earlier this month, Formisano reported finding spectral emissions of methane around a wavelength of 3.3 micrometers. "We have seen methane on Mars," he tells Science. "A very little amount, but the result is clear." Even the apparent concentration of 10.5 parts per billion "is extremely interesting from a scientific point of view," he says, "because you need a source for methane." Otherwise, any methane in the martian atmosphere would be destroyed by solar radiation within a few hundred years.
Either of the two possible sources for martian methane would be noteworthy. It could be oozing out of the interior of the planet through erupting or even quiescent volcanoes, or through hot springs. No sign of such ongoing activity has turned up yet in remote sensing from orbit, although Mars apparently erupted lavas as it cooled into the geologically recent past (Science, 4 August 2000, p. 714).
The other possibility is the Holy Grail and World Cup of astrobiology combined. Bacteria could be living somewhere deep beneath the surface, perhaps chewing on the rock and spewing methane as a byproduct. "I have no reason to exclude one origin or the other," says Formisano. "I can only say we see methane."
Seeing may be believing, but not everyone sees the same molecule in the wiggles and squiggles of a spectrum. "I'm not saying they're wrong," says spectroscopist Michael Mumma of NASA's Goddard Space Flight Center in Greenbelt, Maryland, "but it bears additional confirmation.
That could come soon. Mumma and his colleagues hope to corroborate their reported detection last fall of a methane emission in infrared spectra recorded by ground-based telescopes. And spectroscopist Vladimir Krasnopolsky of the Catholic University of America in Washington, D.C., and his colleagues will report at next month's European Geosciences Union meeting their own detection of methane on Mars. Widely accepted positive results would then create a scramble to identify the source as either bugs or just hot rocks.
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