  Clouds also form in atmospheres of planets that orbit other stars than our
Sun, in so-called extrasolar planets or exoplanets. Exoplanet atmospheres can
be chemically extremely rich. Exoplanet clouds are therefor made of a mix of
materials that changes throughout the atmosphere. They affect the atmospheres
through element depletion and through absorption and scattering, hence, they
have a profound impact on the atmosphere's energy budget. While astronomical
observations point us to the presence of extrasolar clouds and make first
suggestions on particle sizes and material compositions, we require fundamental
and complex modelling work to merge the individual observations into a coherent
picture. Part of this is to develop an understanding for cloud formation in
non-terrestrial environments.
