Strongest evidence yet of extraterrestrial life found, astronomers say

An ocean-covered world bristling with life is the best fit for observations made of a planet 124 light years away in the Leo constellation, a new paper says. Chemical signatures detected on the planet K2-18b points to the strongest evidence of life outside the solar system, according to the peer-reviewed study, published in The Astrophysical Journal Letters. Using the James Webb Telescope, researchers picked up molecules resembling dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) on the planet. On Earth, these chemicals are a sign of microbial life, particularly marine algae. The planet, discovered in 2017 by Canadian scientists in Chile , is 8.6 heavier than the Earth and 2.6 times its diameter. It’s smaller than the gaseous outer planets, such as Neptune, and orbits a cool red dwarf within the star’s habitable zone, where temperatures allow liquid water to exist. This has led scientists to consider K2-18b a hycean planet. An amalgam of the words “ocean” and “hydrogen,” these worlds, in theory, contain a liquid ocean on the surface and an atmosphere rich in hydrogen.

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“Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on hycean worlds,” said Nikku Madhusudhan, an astronomer with the University of Cambridge. “And now we’ve observed it, in line with what was predicted. Given everything we know about this planet, a hycean world with an ocean that is teeming with life is the scenario that best fits the data we have.” Using a mid-infrared instrument, scientists measured the light scattered by the planet as it passed in front of its star. They combed through the data to suss out wavelengths absorbed by K2-18b’s surroundings. Repeated analyses indicated DMS and DMDS counts thousands of times higher than the levels on Earth. “This is an independent line of evidence, using a different instrument than we did before and a different wavelength range of light, where there is no overlap with the previous observations,” said Madhusudhan. “The signal came through strong and clear.” While results are promising, the findings are not conclusive. The data needs to be within five-sigma certainty, meaning less than a one-in-a-million chance the observation is random noise, to be accepted by the scientific community. Madhusudhan and his colleagues will also be conducting lab tests to confirm whether the compounds could be produced by a previously unknown geological process. “It’s important that we’re deeply skeptical of our own results, because it’s only by testing and testing again that we will be able to reach the point where we’re confident in them,” Madhusudhan said. A paper published earlier this week asks whether hycean planets like K2-18b, which completes one orbit every 33 days, could be too hot to have a liquid ocean. The ocean discovered on the planet could be one of magma, the authors say. Madhusudhan and his colleagues say it could take a few more years to confirm their findings. Even if life were not found on K2-18b, future observations with the Webb would put humanity much closer to answering the question of whether we are alone, he notes. “Decades from now, we may look back at this point in time and recognize it was when the living universe came within reach.”