On Earth, oxygen is released by life \u2013 specifically, by organisms using sunlight for energy.<\/p>\n
Oxygen is a very reactive gas. Early in Earth\u2019s history any oxygen released into the atmosphere was rapidly removed.<\/p>\n
It reacted with rocks, or was destroyed by photochemical reactions driven by ultraviolet rays in sunlight.<\/p>\n
More from Lewis Dartnell:<\/strong><\/em><\/p>\n Such processes are known as \u2018sinks\u2019, and oxygen only started to accumulate in Earth\u2019s atmosphere once its production had overwhelmed these sinks.<\/p>\n An oxygen-rich atmosphere is thought to be a sign of flourishing life on a world, which is why astronomers would be so excited about discovering one on an exoplanet.<\/p>\n But is oxygen the only \u2018biosignature\u2019 gas that would indicate the presence of life on an exoplanet?<\/p>\n Might other gases produced by biochemistry also be able to overwhelm the sinks on their exoplanets and accumulate to detectable levels?<\/p>\n Sukrit Ranjan, at Northwestern University, and his colleagues have been investigating this.<\/p>\n The best candidate worlds for detecting such biosignature gases, they argue, are exoplanets orbiting small, cool M-class red dwarf stars.<\/p>\n Such stars emit less ultraviolet radiation than larger, hotter stars like the Sun<\/a>, and so the sinks on those planets are much weaker.<\/p>\n Exoplanets orbiting M-class red dwarfs offer favourable conditions for the accumulation of reactive gases to levels that we could hopefully detect with space telescopes.<\/p>\n![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2021\/08\/02-Apollo-Earth-image-AS08-16-2593-6a6f1d3-e1647940090384.jpeg?quality=90&resize=620%2C499"\" "\\"\"\"\\"\/")
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