Over the past few decades more than 5000 exoplanets have been confirmed. It is expected that more observations, in particular also of reflected light of exoplanets, will be available in the near future. In our work we focus on spectropolarimetric observations in the visible and in the near infrared spectral ranges. We are particularly interested in rocky, Earth-like planets on which biosignatures may be detected. Using VLT (Very Large Telescope) it is not yet possible to obtain spatially resolved spectra or images of exoplanets, but we may test our methods on planets or moons in our solar system. Therefore we observed our own planet like an exoplanet via Earthshine, i.e. the sun-light reflected from Earth towards the Moon and back-reflected from the lunar surface to Earth. For these observations the instruments FORS and CRIRIS+, both mounted on VLT, have been applied. In order to interpret the observations we performed radiative transfer simulations using the Monte Carlo code MYSTIC, which allows us to include all details of the Earth atmosphere-surface system, in particular realistic three-dimensional cloud structures and the two-dimensional surface. We show how spectropolarimetric observations of exoplanets could be used to detect oceans, to infer information about average cloud properties, and to detect atmospheric constituents like for example methane or carbon dioxide. Another planetary body in reach of currently available instrumentation is Titan, which like Earth is a rocky body which exhibits a thin atmosphere. As preparation for future observations we already performed radiative transfer simulations including the Titan atmosphere.

The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)