Carbon monoxide can be deadly to humans, but researchers of a new study suggest they may help in the search for extraterrestrial life.
Exposure to high levels of carbon monoxide, a colorless, odorless, and tasteless gas, can lead to serious tissue damage and death. Astronomers have also assumed that the buildup of this gas in the planet's atmosphere may indicate lifelessness.
Edward Schwieterman, from University of California, Riverside, and colleagues, however, think the gas helps alert scientists of worlds teeming with alien life.
Ancient Earth Had High Levels Of Carbon Monoxide
In a study published in The Astrophysical Journal, Schwieterman and colleagues used computer models to simulate what would happen when carbon monoxide readily builds up in the atmosphere of living planets.
They identified two things that could happen. In one scenario, they found clues from Earth's past.
Today, carbon monoxide cannot accumulate in oxygen-rich Earth because the gas is quickly destroyed by chemical reactions in the atmosphere. This has not always been the case. Three billion years ago, our planet's atmosphere was nearly devoid of oxygen, but the oceans already hosted microbial life.
The model revealed that the ancient inhabited Earth could maintain carbon monoxide levels of about 100 parts per million (ppm), which is far greater than the amount of gas in the atmosphere today.
Carbon Monoxide In Potentially Habitable Planets
In the second scenario, the researchers looked at the photochemistry around red dwarf stars such as the Proxima Centauri, the solar system's nearest stellar neighbor.
Schwieterman and colleagues found that if a planet around these stars were inhabited and rich in oxygen, they should also have extremely high amounts of carbon monoxide.
"Photochemistry around M dwarf stars is particularly favorable for the buildup of CO, with plausible concentrations for inhabited, oxygen-rich planets extending from hundreds of ppm to several percent," the researchers wrote in their study.
Earth-like planets have been found orbiting in the habitable zone of Proxima Centauri and similar stars. This means they could harbor liquid water, which is considered an essential ingredient of life.
"Given the different astrophysical context for these planets, we should not be surprised to find microbial biospheres promoting high levels of carbon monoxide," Schwieterman said. "However, these would certainly not be good places for human or animal life as we know it on Earth."