Cloud Nine Con (CNC) was a half-day online event with interdisciplinary presentations on all topics related to clouds in the atmospheres of exoplanets and brown dwarfs. The event consisted of four keynote presentations, with a number of short contributed presentations in between. Contributed talks broadly fell into the following categories: talks that were interdisciplinary; talks that demonstrated a new open-source code that is broadly relevant to the CNC topics; or talks that provided new ways of thinking about relevant topics connected to clouds.

The recordings of the talks are available here.

The CNC philosophy

Clouds are a major challenge when interpreting spectra of exoplanet and brown dwarfs. Observations have indicated that clouds are abundant in nearly all of their atmospheres. Without a good quantitative understanding of these clouds we will not be able to decipher the fundamental properties of the atmospheres, such as the bulk composition and thermal structure, despite excellent data. Our current physical knowledge is not sufficient to describe the formation process and properties of clouds precisely enough. Models used to interpret observations of cloudy atmospheres often fail to match the observations accurately and even when they are able to reproduce observations, simplified parametric models carry the risk of converging on unphysical solutions. CNC aims to bring together experts in atmospheric and cloud modeling, leaders in exoplanet observations, and pioneers of exoplanet laboratory work. Its goals are to promote exchange and collaboration between the different fields to gain a better understanding of clouds and their modeling in retrievals and atmospheric models.

CNC was intended to be an interdisciplinary workshop on Königstuhl mountain in Heidelberg, Germany. The idea of the workshop was born at the Lorentz Center workshop "Tackling the Complexities of Substellar Objects" in Leiden, the Netherlands, in February 2020. Due to the ongoing COVID pandemic CNC was postponed to 2023, with a half-day online event in August 2021.