Alien hunting technique analyses the atmosphere of distant planets
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A new approach to detecting alien life has been developed by University of Washington scientists that revolves around trying to determine the atmospheric make-up of distant planets.
Until now, alien hunters have focused their efforts on detecting oxygen in the atmosphere as a sign that life exists on the surface.
The new technique involves looking for a different gas mixture that includes abundant methane and carbon dioxide but lacks carbon monoxide.
“This idea of looking for atmospheric oxygen as a biosignature has been around for a long time. And it’s a good strategy - it’s very hard to make much oxygen without life,” said Joshua Krissansen-Totton, who worked on a paper about the new technique.
“But we don’t want to put all our eggs in one basket. Even if life is common in the cosmos, we have no idea if it will be life that makes oxygen. The biochemistry of oxygen production is very complex and could be quite rare.”
The new study looks at the history of life on Earth, the one inhabited planet we know, to find times where the planet’s atmosphere contained a mixture of gases that are out of equilibrium and could exist only in the presence of living organisms - anything from pond scum to giant redwoods.
In fact, life’s ability to make large amounts of oxygen has only occurred in the past one-eighth of Earth’s history.
By taking a longer view, the researchers identified a new combination of gases that would provide evidence of life: methane plus carbon dioxide, minus carbon monoxide.
Researcher professor David Catling said: “Our study shows that this combination would be a compelling sign of life.
“What’s exciting is that our suggestion is doable and may lead to the historic discovery of an extraterrestrial biosphere in the not-too-distant future.”
The scientists looked at all the ways a planet could produce methane, from asteroid impacts, to out-gassing, to reactions of rocks and water.
It concluded that it would be hard to produce a lot of methane on a rocky, Earth-like planet without any living organisms.
Finding methane and carbon dioxide together, without carbon monoxide, would be a strong signal of life, said the researchers.
Non-biological processes such as volcanic eruptions that generated methane and carbon dioxide also produced carbon monoxide.
In addition, carbon monoxide would be “readily eaten” by microbes.
“So, if carbon monoxide were abundant, that would be a clue that perhaps you’re looking at a planet that doesn’t have biology,” said Krissansen-Totton.
Powerful next-generation telescopes such as Nasa’s James Webb space telescope, due to be launched next year, will be able to conduct the first searches for evidence of life in the atmospheres of planets circling distant stars.
Scientists recently shot down theories that a distant star that exhibits unusual dimming and brightening behaviour was caused by an alien megastructure.