The schematic setup of our 2D equatorial band simulations, with our defined Cartesian coordinate system. The simulated band is shown in green. Aerosols with the directions of the gravitational force (red-dashed) and radiation pressure (black dotted) are shown at the substellar point, nightside and morning/evening terminator. The direction of the super-rotating wind that advects the aerosols is shown (green-solid). — astro-ph.EP
Aerosols appear to be ubiquitous in exoplanetary atmospheres. However because our understanding of the physical processes that govern aerosols is incomplete, their presence makes the measurement of atmospheric properties, such as molecular abundance ratios, difficult.
We show that aerosol particles in highly-irradiated exoplanets experience an additional acceleration due to stellar radiation pressure. The strength of this radiative acceleration often exceeds the planet’s gravity and can approach values of ~10-20x gravity’s for low-density planets (typically sub-Saturns) hosting ~0.1–1 micron aerosols.
Since these highly irradiated, low-density planets are often the best targets for atmospheric characterisation with current instrumentation, radiation pressure is likely an important process when considering aerosol dynamics.
We find that radiation pressure accelerates hazes produced by photochemistry at high altitudes to faster terminal velocities, causing them to grow more slowly. Hence, the particles are smaller and have lower mass concentrations in the presence of radiation pressure.
By simulating haze-like aerosols in a 2D equatorial band model, we show that radiation pressure steepens optical slopes in transmission spectra, resulting in less muted molecular features in the Near-IR and gives rise to a correlation between the strength of radiation pressure and the molecular feature amplitude.
Furthermore, the interaction of zonal winds and radiation pressure impacts both the optical slopes and amplitudes on the individual morning and evening terminators.
James E. Owen, Ruth A. Murray-Clay
Comments: Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2508.20175 [astro-ph.EP](or arXiv:2508.20175v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.20175
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Submission history
From: James Owen
[v1] Wed, 27 Aug 2025 18:00:18 UTC (10,746 KB)
https://arxiv.org/abs/2508.20175
Astrobiology
