The Hycean Paradigm in the Search for Life

Atmospheric characterisation of habitable-zone exoplanets is a major frontier of exoplanet science. Recently, a new class of habitable exoplanets, called Hycean worlds, has been proposed which promises to expand and accelerate the search for planetary habitability and life elsewhere. Several temperate Sub-Neptunes have been identified as candidate Hycean worlds orbiting nearby M dwarfs which make them highly conducive for transmission spectroscopy. Recently, we reported the first JWST spectrum of a possible Hycean world, K2-18 b, with detections of multiple carbon-bearing molecules in its atmosphere. In this talk we will report chemical inferences in the atmospheres of multiple candidate Hycean worlds, using high-precision JWST spectroscopy and/or ground-based high-resolution spectroscopy, and their implications for the atmospheric, surface, and interior conditions. Besides atmospheric chemical compositions, we will present constraints on the temperature structures, clouds/hazes, chemical disequilibrium, internal structures, and the possibility of oceans underneath the atmospheres. We will discuss the implications of our findings on the possibility of life on Hycean worlds and prospects for biosignature searches in their atmospheres using JWST and large ground-based facilities.