Scientists detect signature of life on a distant planet, study suggests

Explore the cosmos with the latest discoveries and scientific advancements. Astronomers have identified the most compelling evidence yet for a potential biosignature on the exoplanet K2-18b, hinting at possible past or present life. Utilizing the James Webb Space Telescope, scientists detected chemical signatures suggestive of biological activity. However, researchers and experts remain circumspect, stopping short of confirming definitive proof of life beyond Earth.

Potential Biosignature Detected on Exoplanet K2-18b

Scientists, employing the powerful James Webb Space Telescope, have observed what they describe as the most noteworthy indications to date of a possible biosignature on the exoplanet K2-18b. This biosignature could point to past or present life associated with biological processes. It is crucial to note, however, that the study’s authors and other specialists advise caution and have not announced a conclusive finding of extraterrestrial life.

The research team utilized the James Webb Space Telescope to discern chemical fingerprints in the atmosphere of K2-18b. These fingerprints imply the existence of dimethyl sulfide (DMS) and potentially dimethyl disulfide (DMDS). On Earth, these molecules are exclusively produced by microbial organisms, typically marine phytoplankton.

The detailed study outlining these discoveries was published in The Astrophysical Journal Letters.

K2-18b, a distant world 124 light-years from our planet, is categorized as a Hycean world. According to Nikku Madhusudhan, the lead author and a professor of astrophysics and exoplanetary science at the University of Cambridge, a Hycean world is a potentially habitable planet completely enshrouded in liquid water with a hydrogen-rich atmosphere.

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Madhusudhan and his colleagues initially proposed the Hycean world concept in 2021, based on their assessment that liquid water oceans could exist on K2-18b.

The exoplanet resides within the habitable zone of its star. This signifies it orbits at an optimal distance to maintain liquid water on its surface due to favorable temperature conditions.

“Earlier theoretical investigations suggested that elevated levels of sulfur-based gases, such as DMS and DMDS, were plausible on Hycean worlds,” Madhusudhan stated. “Our current observations align with these predictions. Considering the collective data about this planet, a Hycean world teeming with oceanic life emerges as the scenario that most accurately fits our data.”

James Webb Telescope Detections: Unveiling Atmospheric Clues

Researchers acknowledge the possibility that these molecules could originate from an alternative, non-biological chemical process occurring on the planet.

These recent findings expand upon prior research by the same team. They previously detected carbon dioxide and methane in K2-18b’s atmosphere using Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) and Near-Infrared Spectrograph (NIRSpec) instruments. This new detection was achieved using Webb’s Mid-Infrared Instrument (MIRI).

“This constitutes separate evidence, acquired with a different instrument and a distinct light wavelength range, ensuring no overlap with prior observations,” explained Madhusudhan. “The signal was notably strong and unambiguous.”

Madhusudhan and his fellow researchers concede that further data is necessary to assert direct evidence of life on another world. The team estimates that 16 to 24 hours of supplementary observations with the Webb telescope will be required to potentially solidify their findings.

“It’s essential to maintain a critical perspective on our own findings, as rigorous and repeated testing is the only path to achieving confidence in them,” Madhusudhan emphasized. “This embodies the fundamental process of scientific inquiry.”

Conversely, other experts believe that while these results are promising and generate excitement, validating the existence of extraterrestrial life, and even definitively classifying K2-18b’s planetary type, will necessitate significantly more time and extensive data collection.

Astrophysicist Sara Seager, a professor at MIT, specializing in physics, planetary science, aeronautics, and astronautics, points out that independent research groups have reached distinctly different conclusions about the nature of the planet. Seager was not involved in the current research.

“Some propose a Hycean world, others suggest a hot magma ocean – a planet featuring molten rock beneath a hydrogen-rich atmosphere, representing a highly inhospitable environment – while still others perceive it as a mini-Neptune,” Seager elaborated, referencing planets larger than Earth but smaller than Neptune. K2-18b, for context, possesses 8.6 times the mass and 2.6 times the size of Earth.

Seager suggests that this discovery, currently a biosignature candidate, “will likely remain in the candidate stage for an extended period.”

“For almost a century, astronomers have grappled with the concept that certain atmospheric gases on planets ‘don’t belong’ – implying they are so reactive that their persistent existence requires continuous replenishment, possibly through biological activity,” Seager explained in an email. “This concept originates from James Jeans in 1930, who initially identified molecular oxygen in Earth’s atmosphere as a sign of life, employing comparable logic to establish limits on oxygen levels in Venus’ atmosphere. Now, with thousands of exoplanets under observation, the urge to overinterpret is strong, and some are prematurely drawing conclusions. Regarding K2-18 b, enthusiasm seems to be outpacing concrete evidence.”

‘Exciting Hint’ from Previous Observations

During previous observations of K2-18b, Madhusudhan and his team identified a faint signal that tentatively supported the Hycean world hypothesis.

“We were uncertain if the previous signal was indeed DMS, but even a hint of it provided sufficient impetus to revisit K2-18b with JWST, utilizing a different instrument,” he stated.

The Webb telescope possesses the unique capability to analyze the atmospheres of exoplanets. As exoplanets transit in front of their host stars from Earth’s perspective, light traverses their atmospheres, enabling Webb to detect the chemical fingerprints of the gases present.

Dimethyl sulfide and dimethyl disulfide, belonging to the same chemical family, exhibit overlapping characteristics. This overlap currently hinders definitive differentiation between the two molecules, although the study authors suggest future observations might resolve this ambiguity.

Typical concentrations of dimethyl sulfide and dimethyl disulfide on Earth are extremely low, below one part per billion. However, the team estimates the presence of these molecules on K2-18b to be thousands of times more concentrated.

“The potential inference of these biosignature molecules raises profound inquiries about the processes responsible for their production,” noted study coauthor Subhajit Sarkar, a lecturer in astronomy at Cardiff University in Wales.

Eddie Schwieterman, an assistant professor of astrobiology at the University of California, Riverside, expressed cautious skepticism and keen interest in subsequent research. Schwieterman, who has previously studied K2-18b, was not involved in this recent study.

His research group determined that maintaining the observed dimethyl sulfide levels in K2-18b’s atmosphere would necessitate “a production rate approximately 20 times greater than Earth’s total DMS production.”

“While a high threshold, it remains plausible given that certain regions in Earth’s oceans exhibit significantly higher productivity compared to the global average,” he added. “This threshold also complicates attributing potential DMS to abiotic (non-biological) sources, as these sources would need to be substantially larger than any currently known.”

However, Schwieterman emphasizes that initial validation is required to confirm the actual presence of dimethyl sulfide in K2-18b’s atmosphere. This confirmation necessitates independent validation from multiple research groups analyzing the same data for the chemical signature of these molecules. Madhusudhan indicated that the analyzed data will be publicly released next week to facilitate independent analyses.

Schwieterman advocates for further Webb telescope observations with enhanced statistical significance to rigorously test the interpretation of dimethyl sulfide’s presence. Observing other planets of comparable size within the habitable zones of their respective stars would also be beneficial, though this process will unfold over years.

“I do have at least one reason for skepticism, which is the anticipated presence of ethane (C2H6) alongside DMS/DMDS if these gases were genuinely present,” he noted. “UV radiation from the host star would decompose DMS/DMDS into components predicted to react and form ethane. The absence of ethane raises questions, suggesting either a flaw in our current models or the possibility that DMS/DMDS is not actually present.”

Schwieterman concludes that considerable further investigation is warranted to validate the findings and thoroughly evaluate the biosignature hypothesis presented in the study.

Significance Threshold for Discovery

The research team responsible for the new study reports their observations have achieved a three-sigma level of statistical significance. This corresponds to a 0.3% probability that the detected signals are due to random chance. However, the established threshold for a formal scientific discovery requires reaching a five-sigma level of significance, reducing the probability of chance occurrence to below 0.00006%.

While the present findings do not constitute a definitive detection of dimethyl sulfide and dimethyl disulfide, “it represents a progressive step in the right direction,” commented Dr. David Clements, an astrophysicist at Imperial College London, who was not involved in the research.

Madhusudhan characterizes his team’s findings as a “significant milestone in our pursuit of life beyond Earth,” marking the beginning of a new era in astrobiological exploration.

“In my view, the pivotal question is no longer whether we will discover life, assuming it exists,” he asserted. “We have now demonstrated our capability to achieve this goal with initial findings showing reasonable statistical significance. A more pressing question for humanity is our collective preparedness to confront the discovery of life unlike anything we currently understand. As a society, as a species, we must collaboratively address the fundamental question: what truly defines life beyond our planet?”