VOLCANIC GAS PLUMES’ EFFECTS ON THE SPECTRUM OF VENUS – THE 1.18 µM WINDOW

The composition and the variability of the lower atmosphere of Venus are critical to understanding the surface-atmosphere interactions, the atmospheric evolution and the volatile exchanges between the interior and the atmosphere [1, 2, 3]. The lower atmosphere can be investigated on the near-infrared spectral windows on the nightside, centered at 1.18 µm (0-15 km), 1.74 µm (20-30 km) and 2.3 µm (30-45 km) [4, 5]. The principal gases in a volcanic plume on Venus may well be similar to those on Earth, namely CO₂, SO₂, H₂O and CO. but different relative abundances are expected [6]. Models and observations suggest a constant abundance of water and no known sinks below the clouds (0-45 km) [7, 8], such that abundance variability should produce a signal in the spectrum of Venus, which can be studied at different altitudes using the near-infrared spectral windows on the nightside [9].

On a previous study, we used the Planetary Spectrum Generator (PSG) [10, 11, 12] to simulate the nightside 2.3 µm spectrum of Venus, using a VIRA atmospheric template for temperature and molecular vertical abundance profiles and four aerosol modes, of effective radii of 0.49 µm, 1.18 µm, 1.56 µm and 4.25 µm [13, 14]. We simulated the effect of a volcanic gas plume rising to a ceiling altitude, for species such as H₂O, CO, OCS, HF and SO₂. We concluded that for possible H₂O, CO and OCS plumes that reach 40 km of height detection could be achievable with a minimum SNR ~ 50 [15].

Here, we present new results regarding detectability of H₂O plumes on the 1.18 µm window, with a maximum sensitivity for the altitude range 0-15 km. Furthermore, constraints will be presented regarding retrieval of small H₂O enhancements (<10%) and respective abundance profiles. Our findings will inform future studies with ground-based instrumentation, such as iSHELL/IRTF spectrograph [16], and future space-based instrumentation, such as the VenSpec-H instrument on EnVision [17, 18].

References. (1) Gilmore et al. 2023, Space Sci Rev. (2) Gillmann et al. 2022, Space Sci Rev (3) Wilson et al. 2024, Space Sci Rev (4) Bézard et al. 2009, JGR Planets (5) Tsang et al. 2009, Journal of Quantitative Spectroscopy and Radiative Transfer (6) Gaillard and Scaillet 2014, Earth and Planetary Sciences Letters (7) Bézard and de Bergh 2007, JGR Planets (8) Marcq et al. 2023, Icarus (9) Wilson et al. 2024, Space Science Reviews (10) Villanueva et al. 2018, Journal of Quantitative Spectroscopy and Radiative Transfer; (11) Smith et al. 2013, JGR Planets (12) Dias et al. 2022, Atmosphere (13) Zasova et al. 2006, Cosmic Research; (14) Haus et al. 2010, Icarus (15) Dias et al. 2025, Ivarus (16) Rayner et al. 2022, Publications of the Astronomical Society of the Pacific (17) Robert et al. 2021, EPSC 2021 (18) Neefs et al. 2025, Acta Astronautica.

Funding. JAD acknowledges funding through the research grants UIDB/04434/2020 and UIDP/04434/2020 and a fellowship grant 2022.09859.BD. JTE and SR acknowledge funding by the Belgian Science Policy Office (BELSPO) with the financial and contractual coordination by the ESA Prodex Office (PEA 4000144206).