Abstract

Contributed Talk - Splinter ExoPlanets

Wednesday, 17 September 2025, 14:00

Characterizing Silicate Clouds in Rogue Planets with JWST

Paul Mollière
Max-Planck-Institute für Astronomie

JWST has reopened our window to mid-infrared studies of substellar atmospheres. Of particular interest are the young low-mass brown dwarfs, which are physical analogs of the directly imaged planets. In the absence of a host star to contribute photon noise, these "rogue" or "free-floating" planets can be studied with exquisite signal-to-noise data. Here we present our study of the variable free-floating planet PSO 318 with JWST spectra from 1-20 µm. We show that the atmosphere is characterized by patchy silicate clouds and that the data are sensitive to the structural properties of the cloud grains, such as their shape and degree of polimerization of the SiO4 tetrahedrons. At the same time, we find that the data quality and required model complexity challenge our state-of-the-art inference techniques, such as nested sampling retrievals. We discuss the implications of this finding and how it might be addressed in the future. An alternative that is already available today is to partition the data into wavelength intervals that allow answering "isolated" questions that do not depend on the full wavelength range. Using such an approach, we show how cloud properties can be characterized without performing a full retrieval, thereby speeding up analyses by many orders of magnitude. JWST and future ELT data require us to rethink how we characterize planets, and our approach is one example of how this may happen.