Some aspects of science with a 50-m AO telescope

Among the science challenges of the Extremely Large Telescopes (ELTs),four object types are studied for performance with a 50 m ELT withadaptive optics (AO), Euro50. Emphasis is on planetary systems and verydistant objects. For planetary systems and their evolution, we examinehigh resolution imaging of the nuclei of comets and high-resolutionimaging, photometry and low and intermediate resolution spectroscopy ofKuiper-Belt objects. Imaging of Earth-like planets is discussed. Thevery high contrast imaging necessary for these purposes is discussedtogether with the relevant error sources. Finally, photometry andclassification of supernovae is discussed and examined. The performanceof a 50 m AO ELT is compared to corresponding data obtainable withcurrent VLTs equipped with AO