Carbon monoxide detectors in our homes to warn about the dangerous accumulation of this colorless, odorless gas that we usually associate with death. Astronomers, in fact, also believed that the accumulation of carbon monoxide in the planet’s atmosphere must be a sure sign of lifelessness. And now the research team from the University of California-riverside says: sky carbon monoxide detectors can actually warn us about the presence of simple life forms in a distant world.
Life and carbon monoxide: compatible or not?
“With the launch of the space telescope James Webb in two years, astronomers will be able to analyze the atmospheres of some solid exoplanets,” says Edward Smitherman, lead author and researcher at NASA in the Department of Earth Sciences at the University. “It would be a shame to lose sight of the inhabited world only because we have not considered all the possibilities.”
In the study, which appeared today in The Astrophysical Journal, a team of Smitherman used computer models of the chemistry in the biosphere and the atmosphere to find two intriguing scenarios where carbon monoxide readily accumulates in the atmospheres of planets with life.
In the first scenario, the team found answers to the deep past of our planet. Modern, oxygen-rich Earth, the carbon monoxide cannot accumulate, because the gas is rapidly destroyed by chemical reactions in the atmosphere. But three billion years ago the world was very different. The oceans already teeming with microbial life, but the atmosphere was almost devoid of oxygen, and the sun was much dimmer.
Model team shows that an ancient version of the inhabited Earth was able to keep up the level of carbon monoxide of about 100 parts per million (ppm) is several orders of magnitude greater than parts per billion that are in the atmosphere today.
“This means that we can expect a high content of carbon monoxide in the atmosphere inhabited, but oxygen-poor exoplanets orbiting stars like our own sun,” says Timothy Lyons, one of the authors of the study. “This is an excellent example of the ability to use history as a guide to search for life elsewhere in the Universe”.
The second scenario is more favorable for the accumulation of carbon monoxide: photochemistry around red dwarf stars like Proxima Centauri, the nearest to our Sun the star at a distance of 4.2 light years. Model team predict that if a planet around such a star will be populated and rich in oxygen, we should expect that the carbon monoxide content is extremely high — hundreds ppm to several percents.
“Given the different astrophysical context of such planets, we should not be surprised if we find microbial biosphere, leading to accumulation of high levels of carbon monoxide,” says Smitherman. “Nevertheless, they will certainly be not the best place for living people or animals that walk upon the Earth.”