Possibilities for an Aerial Biosphere in Temperate Sub Neptune-Sized Exoplanet Atmospheres

The search for signs of life through the detection exoplanet atmosphere biosignature gases is gaining momentum. Yet, only a handful rocky atmospheres are suitable observation with planned next-generation telescopes. To broaden prospects, we describe possibilities an aerial, liquid water cloud-based biosphere in sub Neptune-sized temperate exoplanets, those receiving Earth-like irradiation from their host stars. One such planet known (K2-18b) and other candidates being followed up. Sub Neptunes common easier to study observationally than exoplanets because larger sizes, lower densities, extended or envelopes. lack any solid surface as know it, so it worthwhile considering whether can support aerial biosphere. We review, synthesize, build upon existing research. Passive microbial-like particles must persist aloft region clouds long enough metabolize, reproduce, spread before downward transport altitudes that may be too hot kind survive. Dynamical studies needed flesh out quantitative details particle residence times. A Neptune would need part planetary system unstable asteroid belt order meteoritic material provide nutrients, though also efficiently reuse recycle metals. origin most severe limiting challenge. Regardless uncertainties, keep open mind general observational exoplanets.