Which molecule is commonly detected in the atmospheres of exoplanets?

Methane is commonly detected in the atmospheres of exoplanets because it is a stable molecule that forms through both geological and biological processes. On gas giants, methane is a major component of the atmosphere, while on rocky exoplanets, its presence may indicate potential biological activity. Infrared spectroscopy helps identify methane by analyzing its absorption features in planetary spectra. The detection of methane alongside other gases like oxygen and carbon dioxide could suggest possible biosignatures, making it a crucial target in the search for extraterrestrial life. Its stability and distinctive spectral signature make it an ideal molecule for studying planetary atmospheres.