In what could be the first confirmed signs of life outside our solar system, astronomers from the University of Cambridge using the James Webb Space Telescope have announced the detection of chemicals in the atmosphere of exoplanet K2-18b, which is 124 light years from Earth in the constellation Leo.
Significantly, these chemicals are generally only known to be produced on Earth by biological activity.
According to a press release announcing the potentially history-making detection, the JWST spotted the telltale chemical ‘fingerprints’ of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS), in the exoplanet’s atmosphere, a detection that may be “the strongest evidence yet that life may exist on a planet outside our solar system.”
“Given everything we know about this planet, a Hycean world (a habitable ocean-covered world underneath a hydrogen-rich atmosphere) with an ocean that is teeming with life is the scenario that best fits the data we have,” said project leader and the lead author of the study outlining the discovery, Professor Nikku Madhusudhan from Cambridge’s Institute of Astronomy.
Search for Signs of Life Outside our Solar System May Have Finally Hit Paydirt
Due to the extreme distances to planets orbiting other stars, imaging them directly is beyond humanity’s current technology. As a result, scientists have used several indirect methods to search for signs of life, including scanning for radio signals, gravitational waves, or even hypothetical technologies like Dyson Spheres and warp drives. Scientists are also hunting for chemicals in the atmospheres of distant planets that are typically associated with life on Earth.
The former category, which includes several inventive, past and present efforts by the decades-long Search for Extraterrestrial Intelligence (SETI) and the more recent Applied Physics unnamed planetary defense project helmed by Harvard Professor and regular contributor to The Debrief, Dr. Avi Loeb, typically fall under the category of “technosignatures” since they look for unique signs of technology. Searching for biological signs of alien life that may or may not be technologically advanced, such as this latest detection of chemicals often associated with biological activity in an exoplanet’s atmosphere, is frequently called hunting for “biosignatures.”
Previous studies have found other tantalizing biosignatures, including chemicals often associated with life. In 2023, the detection of potential signs of life on K2-18b was made when the JWST spotted both methane and carbon dioxide in its atmosphere. That discovery was a historic first for a planet orbiting within its star’s habitable zone, but was not considered definitive proof of biological activity.
Now, the newly announced detection of either DMS or DMDS may be potentially irrefutable signs of life outside our solar system, as they are only produced by biological activity here on Earth.
The Signal “Came Through Loud and Clear”
“We didn’t know for sure whether the signal we saw last time was due to DMS,” said Madhusudhan of previous hints of DMS found by the JWST’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments, “but just the hint of it was exciting enough for us to have another look with JWST using a different instrument.”
This time, the team used JWST’s MIRI (Mid-Infrared Instrument), which can scan for infrared light across a spectrum different from the NIRISS and NIRSpec. By looking for signs of life in this spectrum, the team found a robust wavelength indicating the presence of the biologically created chemical.
“The signal came through strong and clear,” Madhusudhan said.
“This is an independent line of evidence,” the professor added, “using a different instrument than we did before and a different wavelength range of light, where there is no overlap with the previous observations.”
After confirming the potential historic observation, the results were evaluated for several possible errors. The work was also analyzed independently. Each time, the team came back to the conclusion that they may have found the first potential signs of life outside our solar system.
“It was an incredible realisation seeing the results emerge and remain consistent throughout the extensive independent analyses and robustness tests,” said co-author Måns Holmberg, a researcher at the Space Telescope Science Institute in Baltimore.
Notably, the concentrations of either DMS or DMDS spotted by JWST were thousands of times higher than concentrations found on Earth. According to the Cambridge astronomers, detecting high levels of either of these chemicals on Hycean (ocean) worlds due to large amounts of biological activity was previously predicted.
“Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds,” Madhusudhan explained. “And now we’ve observed it, in line with what was predicted.”
Further Observations Needed to Confirm Signal and Method of Production
Although the findings are tantalizing, the lead astronomer behind the potentially historic detection of signs of life outside our solar system says he will remain “deeply sceptical of our own results,” until they can be tested several more times. “That’s how science has to work,” he said.
Study co-author Savvas Constantinou, also from Cambridge’s Institute of Astronomy, described the team’s findings as a starting point for future investigations “that are now needed to confirm and understand the implications of these exciting findings.”
Based on their calculations, the team believes that 16 to 24 hours of follow-up observations will be needed to move their confidence of detection from the current 0.3% probability that the results occurred by chance (called ‘three-sigma’) to a more robust 0.00006% probability (five sigma). Further observations will also be needed to determine which of the two chemicals they detect, since they possess “overlapping spectral features.”
Before announcing they have found unmistakable signs of life, the researchers will also look for non-biological methods for creating DMS and DMDS that don’t exist on Earth but may occur on K2-18b. Study co-author, Subhajit Sarkar of Cardiff University, said that the mere signs of either chemical pose “profound questions concerning the processes that might be producing them.”
Still, given that both chemicals only occur on Earth from biological processes and models of worlds like K2-18b had predicted these exact findings if life were present, the study’s lead author is also aware of the potential historical nature of his team’s discovery.
“Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach,” said Madhusudhan. “This could be the tipping point, where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering.”
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.