Scientists have proposed a new way to search for life, by looking for an imbalance of certain gases in the atmospheres of other planets.
Published in Science Advances, the team led by Joshua Krissansen-Totton from the University of Washington in Seattle suggest that spotting these chemical imbalances may indicate whether a world has a habitable biosphere.
“Previously, a lot of the focus in the search for life has been on oxygen,” Krissansen-Totton told IFLScience. “However, there are reasons to believe that even if life is common in the cosmos, oxygen-rich atmospheres might be rare.”
Using upcoming telescopes like the James Webb Space Telescope (JWST), due to launch in 2019, we could be able to measure the atmospheric composition of words beyond the Solar System. That ability will be increased by new ground-based telescopes in the 2020s and the 2030s like the Extremely Large Telescope (ELT).
Our planet is rich in oxygen because it is a waste product of photosynthesis, making this gas an attractive prospect for looking for life elsewhere. But that hasn’t always been the case. Only an eighth of our planet’s history has seen life produce large amounts of oxygen – but we’ve obviously had a habitable biosphere for much longer.
So the team examined the history of life on our planet to find times when only living organisms could have produced the mixture of gases in our atmosphere, even without oxygen. They then ruled out other ways gases could be produced, such as asteroid impacts causing ejections of methane from a planet’s interior.
They found that the detection of methane, carbon dioxide, and nitrogen together is an imbalance that suggests organisms must be playing a part. On our planet, this would have been a signature for life about 4 to 2.5 billion years ago, in the Archean eon. During this time microbes were abundant on Earth, but there was a lack of oxygen on our planet.
Similarly, ruling out the presence of other gases carbon monoxide is also important, as this is readily eaten by microbes. Its existence “could tell us that no one’s home,” notes Krissansen-Totton.
Habitability is judged on a number of factors, not just atmospheric composition but a planet’s orbit, size, mass, and the star it orbits too. We’ve found a few promising worlds so far, but it will be down to bigger and better telescopes to hone in on places that might truly be the real deal.
“The discovery of just one instance of life beyond the solar system would tell us that the origin of life is an unremarkable event and that the universe is teeming with life,” said Krissansen-Totton. “It would be amazing to be able look up at the night sky and know that it is full of countless living worlds.”