Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets

Annual variability and seasonal variability can change the planet's reflected flux (including the reflected flux of key spectral features such as O-2 and H2O) by up to factors of 5 and 20, respectively, for the same orbital phase. This variability is best observed with a high-throughput coronagraph. For example, HabEx (4 m) with a starshade performs up to a factor of two times better than a LUVOIR B (6 m) style telescope.

The variability and signal-to-noise ratio of some spectral features depends non-linearly on atmospheric O-2 concentration. This is caused by temperature and chemical column depth variations, as well as generally increased liquid and ice cloud content for atmospheres with O-2 concentrations of <1 per cent PAL.