Last month, the media was abuzz with claims of the ‘strongest evidence yet’ for life having been found on the extrasolar planet, K2-18b. NASA’s James Webb Space Telescope took a spectrum of the chemical composition of the planet’s atmosphere, and among the many elements and compounds detected, faint traces of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) were spotted. These molecules are also present on Earth; they’re produced by minuscule forms of life, mainly plankton, which coincidentally is Earth’s largest producer of oxygen. Whilst they are biomarkers of life on our planet, the researchers stressed their scepticism, emphasising that no life has been detected on the planet thus far.
Scientists had tried fitting various models to the data from the chemical spectrum of K2-18b’s atmosphere, with different models matching different types of exoplanets. Among them, the model for so-called ‘super-earths’ with rocky cores and thin atmospheres doesn’t quite fit the data. Alternative models currently favoured are the hypothetical ‘Hycean’ planet (liquid water oceans beneath a hydrogen-rich atmosphere) or perhaps a ‘mini-Neptune’ with no well-defined solid surface.
No model seems to be an exact fit, leaving the nature and properties of K2-18b a mystery for the foreseeable future. The research is still exciting within the larger scientific community. In recent years, there have been significant technological advancements in exoplanet detection, leading to a total of over 5000 exoplanets deemed ‘confirmed’ to date. 
The James Webb Space Telescope, for instance, has enabled scientists to achieve detailed spectroscopic analyses of the chemicals in exoplanet atmospheres, and advances in machine learning are helping to speed up the process. One key goal of searching for exoplanets is to search for habitability, so astronomers tend to search in stars’ ‘habitable zones’ – where the temperature is not too hot or too cold, and so capable of having liquid water on the planets’ surfaces.
The work being done in searching for habitable exoplanets will continue, as will further research into increasing our knowledge about K2-18b. To support what’s been done already, independent studies that validate the research would certainly be a good sign. However, many questions are still unanswered – we don’t know whether K2-18b even has water, and further analysis is needed to discover if it has a surface that could support life as we know it. Studies of K2-18b and similar exoplanets suggest this may be unlikely, with many scientists favouring the mini-Neptune model as the most likely scenario. Furthermore, as the spectral lines linked to DMS and DMDS are so faint, it’s unclear whether they’re actually present in the atmosphere or are a result of ‘noise’ in the data. Nonetheless, the excitement around potential habitable planets will undoubtedly continue in the coming years as new discoveries further explore the possibility that we aren’t alone in the universe.
