Not so long ago it was unthinkable for respectable scientists to talk about life on Mars. Such talk was best left to X-Files fans. But no longer.
Evidence is building to suggest biological processes might be operating on the red planet, and life on Mars, many scientists believe, is now more a likelihood than merely a possibility.
Tantalizing evidence is accumulating that suggests the red planet is alive, but incontrovertible proof is still lacking. And while the European Space Agency is keen to send a lander to find it, a history of failed life-finding missions at NASA makes Americans more cautious.
"The life on Mars issue has recently undergone a paradigm shift," said Ian Wright, an astrobiologist at the Planetary and Space Sciences Research Institute at the Open University in Britain, "to the extent now that one can talk about the possibility of present life on Mars without risking scientific suicide."
Much of the excitement is due to the work of Vittorio Formisano, head of research at Italy's Institute of Physics and Interplanetary Space.
In February, Formisano presented data at the Mars Express Science Conference at Noordwijk in the Netherlands. If scientists had been quietly excited before seeing Formisano's data, they were frenetic afterward.
Formisano showed evidence of the presence of formaldehyde in the atmosphere. Formaldehyde is a breakdown product of methane, which was already known to be present in the Martian atmosphere, so in itself its presence is not so surprising. But Formisano measured formaldehyde at 130 parts per billion.
To astrobiologists it was an incredible claim. It means huge amounts of methane must be produced on Mars. (While methane lasts for hundreds of years in the atmosphere, formaldehyde lasts for only 7.5 hours.) "It requires that 2.5 million tons of methane are produced a year," said Formisano.
"There are three possible scenarios to explain the quantities: chemistry at the surface, caused by solar radiation; chemistry deep in the planet, caused by geothermal or hydrothermal activity; or life," he added.
And, with no known geological source of formaldehyde on Mars, it's clear where Formisano's suspicions lie.
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