![]() Our results introduce some important caveats to previous suggestions for interpreting CO in planetary atmospheres, particularly for planets orbiting M dwarfs. …the sequence of reactions that ultimately result in tropospheric OH is mediated by NUV radiation that is substantially less plentiful from M-stars such as Proxima Centauri because of lower photosphere blackbody temperatures, with the result that OH production is much less favored and consequently the sinks for CO and CH 4 are much less efficient… Bacon (STSc).Īstrophysical context is all, even if microbial biospheres with high levels of carbon monoxide, as Schwieterman says, “would certainly not be good places for human or animal life as we know it on Earth.” Photochemistry around such stars tells the tale. Image: A rocky planet orbiting Proxima Centauri might sustain liquid water (artist’s depiction). Here the team found that a living world rich in oxygen could support high carbon monoxide levels from hundreds of ppm to several percent. Useful information indeed, but the findings go beyond worlds around G-class stars to include possible habitable planets around M-dwarf stars like Proxima Centauri, already known to host an Earth-sized planet in its habitable zone. 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.” “That means we could expect high carbon monoxide abundances in the atmospheres of inhabited but oxygen-poor exoplanets orbiting stars like our own sun. ![]() To co-author Timothy Lyons (UC-Riverside), that result carries a clear signal: The researchers found through their modeling that a world like this could support carbon monoxide levels of about 100 parts per million, several orders of magnitude higher than the traces we find of the gas in the atmosphere today. Go back several billion years, however, and Earth was a place whose oceans carried an abundance of microbial life, with an atmosphere that was at the same time all but devoid of oxygen, all under a surface lit by a much dimmer Sun. We don’t expect to see high levels of carbon monoxide on life-giving planets because the gas is so quickly destroyed by chemical reactions on our oxygen-rich world. Interestingly, the paper harks back to our own planet’s deep past. The work appears in the Astrophysical Journal. Edward Schwieterman (UC-Riverside) begs to disagree, and a team led by Schwieterman has produced its modeling of biosphere and atmosphere chemistry to focus on living planets that nonetheless support carbon monoxide at levels we should be able to detect. ![]() ![]() It’s carbon monoxide, which in some quarters has been considered to be the opposite of a biosignature, a clear sign, if detected in sufficient abundance, that a planet is not inhabited. ![]() One gas has turned out to be controversial. We’re moving into the era of biosignature observation by studying the atmospheres of such planets through instruments like the James Webb Space Telescope, and the effort to catalog the combinations of atmospheric gases that point to life is intense and ongoing. Biosignature gases are those that can alert us to the possibility of life on a planet around another star. ![]()
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