Brief Summary
This episode of StarTalk explores the recent detection of potential biomarkers on the exoplanet K2-18b, sparking excitement and skepticism in the scientific community. The discussion covers the methods of detecting life indirectly through atmospheric gases, the nature of K2-18b as a possible Hycean world, and the significance of molecules like dimethyl sulfide (DMS) as potential indicators of life. The conversation also addresses the statistical confidence levels of the data and the challenges of interpreting biomarker detections as definitive proof of life, emphasizing the need for more data and continued investigation.
- Detection of potential biomarkers on exoplanet K2-18b.
- Discussion of Hycean worlds and the significance of methane and dimethyl sulfide (DMS).
- Examination of statistical confidence levels and the need for more data.
What's Up With K2-18b?
The discussion begins with the announcement of potential biomarkers on the exoplanet K2-18b, located 120 light-years away and discovered by the Kepler mission. The focus is on detecting life indirectly by identifying gases in the planet's atmosphere that are associated with biological processes. The detection method involves analyzing light from the star that passes through the exoplanet's atmosphere, with the James Webb Space Telescope (JWST) being crucial for these measurements due to its advanced capabilities. K2-18b is noted for having a "puffy atmosphere," which is advantageous for detection due to its low surface gravity, warm temperature, and light molecular gases.
Hycean Worlds & Detecting Biomarkers
The conversation shifts to the possibility of K2-18b being a Hycean world, characterized by a thin hydrogen atmosphere and a surface ocean. If K2-18b is indeed a Hycean world, the presence of methane alone would strongly suggest the existence of life, as it would be difficult to sustain methane in such an atmosphere without a biosphere. The detected methane levels are significantly higher than expected in the absence of life. In addition to methane, stronger evidence for dimethyl sulfide (DMS) and dimethyl disulfide was reported, molecules typically produced by phytoplankton in Earth's oceans.
When Biomarkers Don’t Mean Life
The discussion addresses the skepticism surrounding the interpretation of biomarkers. If K2-18b is a shrunken Neptune-like planet without a true surface, methane and other gases could be produced in the planet's interior and rise to the upper atmosphere through convection, making the presence of methane less indicative of life. Dimethyl sulfide (DMS), a molecule also found in truffles, is typically produced by phytoplankton on Earth. The concentration of DMS on K2-18b is 10,000 to 100,000 times higher than on Earth, suggesting a potentially thriving biota if the detection and biological origin are confirmed.
Could We Be Wrong?
The validity of the data and its interpretation are contested within the scientific community. The claimed significance level of three sigma for the detection of DMS is met with skepticism, with concerns about the strength of the signal within the spectrum. The process of narrowing down the list of possible molecules to boost the significance level is also questioned. A two-sigma result, which has a 5% chance of being a spurious detection, is compared to the more stringent five-sigma standard used in high-confidence discoveries like the Higgs boson.
Getting More Data with JWST
The discussion emphasizes that no single molecule can be considered definitive proof of life, and the scientific community remains skeptical due to the possibility of unknown geological processes producing these molecules. Scientists aim to reduce uncertainty through more and better data, and further observations by JWST are expected to be proposed to gather additional evidence. The exoplanet's 33-day orbital period makes it relatively convenient for repeated observations during transits. Despite its close orbit, the cooler nature of the star places K2-18b within the habitable zone, making it a potentially "dope world" for further study.
