Aerosol dynamics on hot exoplanets: the role of radiation pressure
File(s)
Published version
Author(s)
Owen, James E
Murray-Clay, Ruth A
Type
Journal Article
Abstract
Aerosols appear to be ubiquitousin exoplanetary atmospheres. However, because our understanding of the physical processesthat
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
∼ 10–20× gravity’s for low-density planets (typically sub-Saturns) hosting ∼0.1–1μm aerosols. Since these highly irradiated,
low-density planets are often the best targets for atmospheric characterization 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.
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
∼ 10–20× gravity’s for low-density planets (typically sub-Saturns) hosting ∼0.1–1μm aerosols. Since these highly irradiated,
low-density planets are often the best targets for atmospheric characterization 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.
Date Issued
2025-10-01
Date Acceptance
2025-08-22
Citation
Monthly Notices of the Royal Astronomical Society, 2025, 543 (1), pp.587-607
ISSN
0035-8711
Publisher
Oxford University Press (OUP)
Start Page
587
End Page
607
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
543
Issue
1
Copyright Statement
© The Author(s) 2025. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
License URL
Publication Status
Published
Date Publish Online
2025-08-23