Photo credit: www.sciencedaily.com
Astronomers have reported groundbreaking findings that suggest potential biosignatures beyond our solar system, though they approach these insights with careful consideration.
In a study led by the University of Cambridge, scientists utilized the James Webb Space Telescope (JWST) to identify chemical signs of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) in the atmosphere of the exoplanet K2-18b, which resides in its star’s habitable zone.
On Earth, DMS and DMDS are exclusively produced by living organisms, particularly by marine microorganisms such as phytoplankton. While there exists the possibility that unknown chemical processes may generate these substances in K2-18b’s atmosphere, the findings offer compelling evidence that life could potentially thrive on this distant planet.
The statistical confidence of these observations has reached the ‘three-sigma’ level, indicating that there is only a 0.3% chance these results occurred randomly. For these findings to be classified as a significant scientific breakthrough, they would need to achieve a five-sigma threshold, decreasing the likelihood of coincidence to below 0.00006%.
The research team believes that an additional 16 to 24 hours of follow-up observations with the JWST may help to attain the critical five-sigma significance. Their findings have been published in The Astrophysical Journal Letters.
Previous observations of K2-18b, which is 8.6 times more massive and 2.6 times larger than Earth, located 124 light-years away in the constellation Leo, had already revealed the presence of methane and carbon dioxide in its atmosphere. This marked the first detection of carbon-based molecules in the atmosphere of an exoplanet situated in a habitable zone, supporting the notion of a ‘Hycean’ planet—a world covered mostly by oceans under a hydrogen-rich atmosphere.
Nevertheless, an earlier, weaker signal suggested the possibility of DMS. “While we were uncertain whether the earlier signal was truly indicative of DMS, its mere hint prompted us to investigate further with JWST using a different instrument,” remarked Professor Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who spearheaded the research.
To analyze the atmospheric composition of distant exoplanets, astronomers examine the light from the host star as the planet transits across it. As K2-18b moves in front of its star, the JWST detects a reduction in stellar brightness; a small fraction of the starlight filters through the planet’s atmosphere, which alters the light, leaving chemical signatures that scientists can study to identify the gases present.
The previous tentative identification of DMS was made using JWST’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments, which analyze a wavelength range in the near-infrared (0.8-5 microns). The latest results were obtained using JWST’s MIRI (Mid-Infrared Instrument) focusing on the mid-infrared range (6-12 microns).
“This new insight provides independent evidence, utilizing different instruments and a distinct range of light, ensuring no overlap with earlier observations,” Madhusudhan stated. “The signal was both strong and clear.”
“It was an exhilarating moment to see the data consistently align during extensive independent analyses and rigorous robustness tests,” noted co-author Måns Holmberg, a researcher at the Space Telescope Science Institute in Baltimore, USA.
DMS and DMDS are chemically related, both recognized as potential biosignatures. Their spectral characteristics overlap in the measured wavelengths, though further analysis will clarify their distinctions.
Interestingly, DMS and DMDS concentrations on K2-18b are vastly different from those on Earth, where levels are generally below one part per billion. On K2-18b, concentrations could exceed ten parts per million, suggesting a highly active environment.
“Theoretical models have long suggested that elevated levels of sulfur-based gases such as DMS and DMDS could exist on Hycean worlds,” Madhusudhan explained. “Now, our observations align with those predictions. Considering all available data, a scenario where K2-18b hosts an ocean teeming with life appears most likely.”
While enthused by the findings, Madhusudhan emphasizes the need for more data before asserting the presence of life. He expresses cautious optimism, yet acknowledges the potential for unknown chemical mechanisms influencing K2-18b’s atmosphere. Collaborative efforts are underway to explore whether DMS and DMDS can be formed through non-biological processes at the observed levels.
“Our findings raise significant questions about the potential sources of these biosignature molecules,” remarked co-author Subhajit Sarkar from Cardiff University.
“This research lays the groundwork for future inquiries necessary to validate and comprehend the implications of these remarkable discoveries,” added co-author Savvas Constantinou from Cambridge’s Institute of Astronomy.
“Being critically evaluative of our results is essential. Through repeated testing, we aim to establish a solid foundation of confidence in our conclusions,” Madhusudhan stressed. “This is the essence of the scientific method.”
While definitive claims remain premature, Madhusudhan believes that with advanced tools like JWST and upcoming telescopes, humanity is progressively inching closer to answering one of its most fundamental inquiries: is there life beyond Earth?
“Years ahead, we might look back on this pivotal moment as the time we began to grasp the possibilities of a living universe,” reflected Madhusudhan. “This could be a turning point in our quest to determine whether we are alone in the cosmos.”
The James Webb Space Telescope is a collaborative project between NASA, ESA, and the Canadian Space Agency (CSA), with support from a UK Research and Innovation (UKRI) Frontier Research Grant.
Source
www.sciencedaily.com