Scientists on Thursday confirmed the presence of methane on Mars, raising two possibilities: volcanos, or life on the red planet.
"Methane should be short-lived in that atmosphere. It should last for less than a few hundred years," Andrew Coates, of the Mullard space science laboratory at University College London, told the British Association science festival in Exeter, England.
"So there must be a very recent source, perhaps even a current source. The two possible sources could be volcanism -- very recent or current volcanism -- or life. All life as we know it on Earth, even down to the tiniest microbe, produces methane as a byproduct."
Mars was once an active planet: Mons Olympus on Mars is the biggest volcano in the solar system. But the planet has not been volcanic on any large scale for at least 3.8 billion years. So even if the source of the methane is geological rather than biological, the discovery is enough to set pulses racing in planetary science laboratories.
Either way, the red planet can no longer be considered a dead planet.
There is tentative evidence of relatively recent, small-scale volcanism.
"So there is certainly a good chance that it could be volcanism," Coates said. "But we have to admit a second possibility, that life is producing it. I think that it is a long shot. What we have to do is look at the evidence, look at the Mars Express data in particular, and this is what people are trying to do at the moment."
The concentrations of methane are tiny: no more than ten parts per billion in the wispy Martian atmosphere. But if Mars is a dead planet -- the assumption when the Viking landers first touched down on its cold, arid surface in 1976 -- then there should be no methane at all.
Since 1996, after the tantalizing discovery of what looked like strange fossil bacteria in a meteorite known to have come from Mars, European and US scientists have hoped for evidence of bygone life.
In the past year four spacecraft have arrived at the planet, including Britain's ill-fated Beagle 2, the only mission specifically designed to look for life on Mars.
Scientists have also recently confirmed that Mars was once washed by huge rivers, lakes and ancient seas, that it is losing up to 100 tonnes of atmosphere every day, so that its atmosphere must once have been as dense, or even much denser, than Earth's, and that it would once have been a warm, active planet. So the conditions for life would have existed 4 billion years ago.
The requirements for life are water and warmth. Volcanic activity could be evidence of enduring warmth, and the presence of surviving water on Mars has also been confirmed again and again in the latest round of exploration.
"There is a possibility it is volcanism. There is a possibility again that it is life. So it is a key discovery," Coates said.
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