The detection of life beyond Earth would be one of the most profound discoveries in the history of science. The Milky Way galaxy alone hosts hundreds of millions of potentially habitable planets. Astronomers are using powerful space telescopes to look for molecular indicators of biology in the atmospheres of the most Earth-like of these planets. But so far, no solid evidence of life has ever been found beyond the Earth. A paper published in April 2025 claimed to detect a signature of life in the atmosphere of the planet K2-18b. And while this discovery is intriguing, most astronomers ' including the paper's authors ' aren't ready to claim that it means extraterrestrial life exists. A detection of life would be a remarkable development. The astronomer Carl Sagan used the phrase, 'Extraordinary claims require extraordinary evidence,' in regard to searching for alien life. It conveys the idea that there should be a high bar for evidence to support a remarkable claim. I'm an astronomer...
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