The best evidence for life outside our solar system just got stronger
Researchers say these biosignatures on exoplanet K2-18b could be the "tipping point" to answering the biggest question in planetary science: Are we alone?
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FILE VIDEO: This video tours Arp 142, an interacting galaxy pair affectionately known as the Penguin and the Egg that lies 326 million light-years from Earth. (Video courtesy: NASA)
Thanks to NASA's powerful James Webb Space Telescope (JWST), astronomers have found the best evidence yet of life on another world outside our solar system.
For years, the exoplanet K2-18b has been a top contender with promising signs of life. New research led by the University of Cambridge has found evidence of chemicals within K2-18b's atmosphere that on Earth are produced by marine life, like algae and phytoplankton.
K2-18b orbits its parent star within the constellation Leo, 124 light years away, and is more than 2.5 times larger than Earth. This world is known as a "Hycean" planet because it could contain an ocean underworld teeming with life and a hydrogen-rich atmosphere.
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Previous observations have found methane and carbon dioxide in the exoplanet’s atmosphere, with hints of other promising signatures, but this new research confirms a "chemical fingerprint" of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS). These chemicals are from the same family and are believed to be biosignatures produced by life.
This artist’s concept shows what exoplanet K2-18 b could look like based on science data. K2-18 b, an exoplanet 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. (Illustration: NASA, CSA, ESA, J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University) / NASA)
"We didn’t know for sure whether the signal we saw last time was due to DMS, but just the hint of it was exciting enough for us to have another look with JWST using a different instrument," said Professor Nikku Madhusudhan, of Cambridge’s Institute of Astronomy, who led the research.
Earlier research used JWST’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments. The new observations used JWST’s MIRI (Mid-Infrared Instrument) to find a "strong and clear" signal of DMS and DMDS, according to Madhusudhan.
These chemicals are found within Earth’s atmosphere, but the concentrations on K2-18b are estimated to be thousands of times stronger, about 10 parts per million, according to the researchers.
Transmission spectrum of the habitable zone exoplanet K2-18 b using the JWST MIRI spectrograph. (Credit: A. Smith, N. Madhusudhan)
"Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds," Madhusudhan said. "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."
The researchers say this could be a "tipping point" to answering the biggest question in planetary science: Are we alone?
As with all things in science, these exciting findings have produced more questions, including what processes are producing the chemical signatures on the exoplanet. More observations and experiments are needed to determine the underlying cause, including any non-biological possibilities.