Observing Exoplanetary Ozone In The Mid-Ultraviolet

There are good reasons for pushing the spectral range of observation to shorter wavelengths than currently envisaged for terrestrial planet-finding missions utilizing with a 4-rn, diffraction-limited, optical telescope: (1) The angular resolution is higher, so that the image of an exoplanet is better separated from that of the much brighter star. (2) Due to the higher resolution, the exozodiacal background per resolution element is smaller, so exposure times are reduced for the same incident flux. (3) Most importantly, the sensitivity to the presence of life on habitable exoplanets is increased by a hundred-fold by access to the ozone biomarker at 250-300 nm. These benefits must be weighed against challenges arising from the faintness of exoplanets in the mid-UV. We will describe the benefits and the technical and cost challenges.