Earth’s carbon copy may be out there
The secret to determining whether distant planets host oceans, and potentially life, could be contained in their atmospheres, scientists have argued.
In a new paper, researchers have proposed that the easiest way to spot other habitable planets may be to measure what they lack, rather than what they have – specifically, carbon dioxide.
In our own solar system, Venus and Mars have atmospheres that are around 95% CO². On Earth, it is a lot less than 1%.
The total proportion of carbon on each is the same, but on Earth it has been removed from the atmosphere, in a large part thanks to processes involving the ocean.
Amaury Triaud, from the University of Birmingham in England, said that if one planet in a solar system had significantly less CO² in its atmosphere than the others, then this was of interest.
“There’s only one way to remove carbon
dioxide from an atmosphere, and that’s water or life, with water being by far the most efficient,” he said.
In the past two decades, scientists have discovered thousands of exoplanets – planets orbiting stars other than our own. Many are in the so-called “habitable zone”, where it would be possible to have liquid water, which it is assumed makes life far more likely. Finding out whether they do have water, though, is extremely difficult.
In the paper, published in the journal Nature Astronomy, Triaud and his colleagues argue that CO² could help to narrow the search.
The lack of CO² on its own is not proof of life. But with so many planets to look at, it may help astronomers know where to focus their efforts.
Dr Julien de Wit, assistant professor of planetary sciences at the Massachusetts Institute of Technology, was a co-author of the paper. He said current technology might be able to pick up on some of these more subtle clues.
“One of the signs of carbon consumption by biology is the emission of oxygen. Oxygen can transform into ozone, and ozone has a detectable signature right next to CO²,” he explained.
“So observing both at once can inform us about habitability, but also about the presence of life on that planet.”