Exoplanets & Exomoons

Scattering Transparency of Clouds in Exoplanet Transit Spectra

By Keith Cowing
Status Report
June 27, 2023
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Scattering Transparency of Clouds in Exoplanet Transit Spectra
Manifestation of the scattering transparency effect in the transit spectrum of TRAPPIST-1e system having a water cloud with 𝜏=1 and 𝑍c=100 km. The transit spectrum is simulated with MC calculations for cloud particles having an π‘Ÿeff=20 Β΅m. The dashed lines are the spectra obtained for constant values of 𝑔. The actual spectra, after considering the spectral variations of 𝑔, are shown in bold lines. They are obtained by interpolating among the dashed spectra. The blue curves do not consider the spectral variations of πœ” whereas the red curves consider the realistic variation πœ” for water clouds which leads to the spectral features of water droplets. Gas absorption is not considered. The spectral rise towards shorter wavelengths in the dashed curves is due to Rayleigh scattering. A color gradient for 𝑓 Γ— πœ”, which is a measure of scattering transparency, is shown in the background. This gradient of 𝑓 Γ— πœ” is same as that shown in figure 3 for TRAPPIST-1e system. — astro-ph.EP

The presence of aerosols in an exoplanet atmosphere can veil the underlying material and can lead to a flat transmission spectrum during primary transit observations.

In this work, we explore forward scattering effects from super-micron sized aerosol particles present in the atmosphere of a transiting exoplanet. We find that the impacts of forward scattering from larger aerosols can significantly impact exoplanet transits and the strength of these effects can be dependent on wavelength. In certain cloud configurations, the forward-scattered light can effectively pass through the clouds unhindered, thus rendering the clouds transparent.

The dependence of the aerosol scattering properties on wavelength can then lead to a positive slope in the transit spectrum. These slopes are characteristically different from both Rayleigh and aerosol absorption slopes. As examples, we demonstrate scattering effects for both a rocky world and a hot Jupiter.

In these models, the predicted spectral slopes due to forward scattering effects can manifest in the transit spectrum at the level of ∼10s to ∼100s of parts per million and, hence, could be observable with NASA’s James Webb Space Telescope.

Bhavesh Jaiswal, Tyler D. Robinson

Comments: 9 pages, 7 figures, published in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2306.12911 [astro-ph.EP] (or arXiv:2306.12911v1 [astro-ph.EP] for this version)
Submission history
From: Bhavesh Jaiswal
[v1] Thu, 22 Jun 2023 14:24:18 UTC (1,038 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) πŸ––πŸ»