In an exciting breakthrough for the field of astrobiology, astronomers have uncovered the most compelling signs yet of a potential biosignature beyond our solar system. The researchers, led by a team from the University of Cambridge, utilized data gathered from the groundbreaking James Webb Space Telescope (JWST) to detect the chemical signatures of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) in the atmosphere of an exoplanet known as K2-18b. This planet orbits its star within the habitable zone, a region where conditions may be suitable for life.

On Earth, DMS and DMDS are molecules that are primarily produced by living organisms, particularly by marine phytoplankton. This raises the tantalizing possibility that similar processes could be occurring on K2-18b, although researchers remain cautious, acknowledging that there could be unknown chemical processes that might account for these molecules in the planet's atmosphere.

The significance of the findings is underscored by the statistical analysis of the data, which has reached the 'three-sigma' level of significance. This means there is only a 0.3% chance that these observations are due to random chance. However, to meet the rigorous standards of scientific discovery, the results must achieve a 'five-sigma' threshold, indicative of a probability of less than 0.00006% that they are a fluke. The research team estimates that between 16 to 24 additional hours of observation with JWST could help them reach this crucial level of significance.

The results of this research have been published in the esteemed journal The Astrophysical Journal Letters. K2-18b is particularly intriguing; it is 8.6 times more massive and 2.6 times larger than Earth, located approximately 124 light-years away in the constellation of Leo. Previous observations of K2-18b had already revealed the presence of methane and carbon dioxide in its atmosphere, marking it as the first known exoplanet in the habitable zone where carbon-based molecules were detected. This aligns with models predicting the existence of 'Hycean' planetsworlds covered in oceans beneath hydrogen-rich atmospheres.

Interestingly, earlier findings had hinted at a weaker signal that could indicate the presence of DMS. Professor Nikku Madhusudhan, who led the research at Cambridge's Institute of Astronomy, expressed enthusiasm over the potential findings: 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.

To analyze the atmospheres of distant planets, astronomers examine the light from the parent star as the planet transitscrossing in front of the star as viewed from Earth. During K2-18b's transit, JWST detected a decrease in stellar brightness, allowing a tiny fraction of starlight to pass through the planet's atmosphere before reaching Earth. This absorption leaves distinctive signatures in the stellar spectrum, enabling astronomers to deduce the composition of the exoplanet's atmosphere.

The initial inference regarding DMS was gathered using JWST's NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments, which analyze wavelengths in the near-infrared range (0.8-5 microns). The new findings, however, come from observations made with the JWST's MIRI (Mid-Infrared Instrument), which operates in the mid-infrared range (6-12 microns). Professor Madhusudhan remarked, 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. The signal came through strong and clear.

Mns Holmberg, a co-author of the study and researcher at the Space Telescope Science Institute in Baltimore, USA, shared the thrill of the discovery: It was an incredible realization seeing the results emerge and remain consistent throughout the extensive independent analyses and robustness tests. Both DMS and DMDS are molecules within the same chemical family, with both predicted to serve as biosignatures. However, the concentrations of these molecules in K2-18bs atmosphere differ significantly from those on Earth, where they typically exist at fewer than one part per billion. In contrast, K2-18b is estimated to host concentrations of these molecules that are thousands of times higherover ten parts per million.

Professor Madhusudhan noted, Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds. 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. Despite the encouraging findings, Madhusudhan emphasizes the necessity of acquiring more data before definitively claiming that life exists on another planet. He remains cautiously optimistic but acknowledges the possibility of unknown chemical processes at play.

Co-author Subhajit Sarkar from Cardiff University pointed out, The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them. In agreement, co-author Savvas Constantinou from Cambridges Institute of Astronomy stated, Our work is the starting point for all the investigations that are now needed to confirm and understand the implications of these exciting findings. Madhusudhan reiterated the importance of skepticism in scientific research, asserting, Its 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.

While Madhusudhan stops short of declaring a definitive discovery at this stage, he affirms that with the advanced capabilities of JWST and future telescopes, humanity is embarking on a journey to answer one of the most profound questions of all: are we alone in the universe? He remarked, Decades from now, we may look back at this point in time and recognize it was when the living universe came within reach. 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. The James Webb Space Telescope represents a collaborative effort among NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), and this research has received support through a UK Research and Innovation (UKRI) Frontier Research Grant.