Carbon monoxide detectors could reveal aliens

Carbon monoxide (CO), a deadly gas to humans, is being considered an indicator of Life on distant planets.

For many years astronomers had believed that a build-up of CO in the atmospheres of distant planets would be a good sign that those planet would be unable to harbour Life.

There are estimated to be hundreds of billions of planets in the Milky Way, and scientists are trying to narrow down which ones to point their telescopes at.

However that may easier said than done, according to a team of researchers from the University of California, Riverside, who have now produced evidence suggesting that planets shouldn't be discounted because of the presence of carbon monoxide in their atospheres.

In their study published in the Astrophysical Journal, the team argues that "celestial carbon monoxide detectors may actually alert us to a distant world teeming with simple Life forms".

Dr Edward Schwieterman's team has devised two scenarios in which carbon monoxide would build up in the atmospheres of planets which harbour Life.

He said: "With the launch of the James Webb Space Telescope two years from now, astronomers will be able to analyse the atmospheres of some rocky exoplanets.

"It would be a shame to overlook an inhabited world because we did not consider all the possibilities," added Dr Schwieterman, lead author of the study and a NASA fellow.

Image:Another new NASA telescope could find 1,400 planets. Pic: NASA

In the first scenario which Dr Schwieterman's team developed, they noted although the modern Earth's oxygen-rich atmosphere doesn't allow carbon monoxide to build up because of chemical reactions in the atmosphere, this wasn't always the case.

Three billion years ago, the Earth's oceans were already teeming with microbial Life, but the atmosphere was almost devoid of oxygen - and the sun was much dimmer.

According to their simulated models of the ancient Earth's atmosphere, it could have had CO levels of roughly 100 parts per million (ppm) which is magnitudes higher than the parts per billion in the atmosphere today.

"That means we could expect high carbon monoxide abundances in the atmospheres of inhabited but oxygen-poor exoplanets orbiting stars like our own sun," said Professor Timothy Lyons, one of the study's co-authors.

"This is a perfect example of our team's mission to use the Earth's past as a guide in the search for Life elsewhere in the universe," added Professor Lyons, who is a director at UCR's Alternative Earths Astrobiology Centre.

Image:There is a limited distance from stars in which planets could sustain Life. Pic: NASA

The team's second scenario features an even more favourable situation for CO build-up, and describes the environment around red dwarf stars like Proxima Centauri, the star nearest to our sun, only 4.2 light years away.

Around stars like Proxima Centauri, if the planets were inhabited and had a lot of oxygen, then there would also be an abundance of carbon monoxide in the atmosphere, from hundreds of pps up to several percent.

"Given the different astrophysical context for these planets, we should not be surprised to find microbial biospheres promoting high levels of carbon monoxide," Dr Schwieterman said.

"However, these would certainly not be good places for human or animal Life as we know it on Earth."

Rocky planets the size of Earth have been discovered in the habitable zones of stars such as Proxima Centauri, and thus could harbour liquid water.

Scientists say these planets would ideal for deeper study using NASA's new James Webb Space Telescope, which is scheduled to launch in March 2021.