If life still exists on the Red Planet, it must be very rare – or so an unexploited energy source in the atmosphere suggests.
The Martian atmosphere is unusually rich in carbon monoxide, which many microbes here on Earth can convert to carbon dioxide to yield energy for growth.
“It’s a free lunch, just sitting in the atmosphere, that microbes could be eating,” says Steven Sholes, an astrobiologist at the University of Washington. The persistence of that leftover lunch suggests that Martian life must be nonexistent, or at least very rare.
To determine just how rare, Sholes gathered estimates of how quickly solar radiation generates carbon monoxide in the Martian atmosphere, and how fast it diffuses down to the planet’s surface and into subsurface rocks, where any Martian life would be sheltering from deadly radiation. Then he used these estimates to calculate the maximum subsurface microbial biomass that could be consuming carbon monoxide, yet still leave the observed amount of leftovers.
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