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Transmission spectroscopy along the transit of Venus used for probing the atmosphere’s upper layers and as a proxy for exoplanets atmosphere characterization

Presentation #406.06 in the session Venus (Poster + Lightning Talk)

Published onOct 23, 2023
Transmission spectroscopy along the transit of Venus used for probing the atmosphere’s upper layers and as a proxy for exoplanets atmosphere characterization

Transmission spectroscopy probes the atmospheric limb of a transiting planet. We will present our study using spectroscopic transmission techniques upon observations of the last Venus’ transit, related with the spectral region impacted by Mie scattering, sulfur dioxide, carbon dioxide and the UV absorber. We took advantage of previous studies in this scope in order to prepare our research protocol [1,2,3].

In this work, we retrieved transmission spectra of the atmosphere of Venus, using high resolution observations performed with FIRS/Dunn Solar Telescope(USA), our aim was to produce a case study where we compare the retrieved spectroscopic transmission observables on Venus with the datasets obtained by space probes and ground-based observations, which will consist in a valuable calibration template and an unique opportunity to assess the feasibility of the atmospheric characterization of Earth-size exoplanets near the habitable zone with the transmission spectroscopy technique and provide an invaluable proxy for the atmosphere of such a planet.

The altitudes probed with this transmission spectroscopy technique on Venus present a lower absorption value at about 80 km [4] due to the dominant diffusion regime, in the case of Venus, the most remarkable and extended spectral signature is that of Mie scattering by the upper haze (only composed by mode-1 particles), below that altitude large particles (mode-2) start to be dominant which turn the Rayleigh scattering more prominent which only could be reached at 2.65 microns or higher wavelengths [5,6].

Previous transmission spectroscopy studies have provided insights into the atmospheric composition, structure and dynamics of hot giant exoplanets. In this context, Venus can provide an essential proxy for a telluric exoplanet. Venus transmission spectrum obtained during its transit across the Sun will serve both as a comparison basis for transiting Earth-mass exoplanets to be observed in the future, and a proof of feasibility that such observations can effectively probe the atmospheres of exoplanets in this mass range. In addition, transit observations of Venus can bring precious information about how the atmosphere of a non-habitable world – observed as an exoplanet – differs from that of an habitable planet, such as Earth’s [7].

References: [1] Pasachoff, et al., A. J. 141, 112 (2011), [2] Tanga, et al., Icarus 218, 207–219 (2012), [3] Widemann, T., et al., EPSC2012-412-4, [4] Ehrenreich, D., et al., A&A 537 (2012), [5] Ehrenreich, D., 2006, A&A, 448, 379, [6] Kaltenegger, L., Traub, W. A. 2009, ApJ, 698, 519, [7] Vidal-Madjar, et al. 2010, A&A, 523, A57

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