The EnVision VenSpec Ground-Based Observations Working Group: Current Activities and Future Plans

EnVision is ESA’s upcoming Venus orbiter, planned to begin science operations at Venus in 2034. The mission is designed to investigate Earth’s sister planet as an integrated system, spanning its deep interior, surface, lower atmosphere, and upper atmosphere [1]. EnVision will address key questions concerning Venus’ geological history, present-day surface and atmospheric activity, and the coupled evolution of its interior, surface, atmosphere, and climate. To achieve these objectives, the spacecraft will operate in a low-altitude polar orbit, enabling its payload to observe the Venusian surface and atmosphere at high spatial and spectral resolution. Among its instruments is the VenSpec suite, which consists of three spectrometers [2]: VenSpec-U, operating in the ultraviolet range of 190–380 nm [3]; VenSpec-H, covering 1.16–2.48 µm [4]; and VenSpec-M, covering 0.79–1.51 µm [5]. Together, these instruments will characterize atmospheric trace gases and chemistry, search for volcanic gas plumes above and below the cloud deck, and map surface emissivity and composition.

To support EnVision, and in particular the VenSpec suite, the Venus Ground-Based Observations Working Group has been established to enhance the mission’s scientific return through coordinated observations from Earth-based facilities [6]. The Working Group has three main objectives. First, it aims to provide spectroscopic datasets across relevant wavelength ranges to help evaluate observing strategies and develop retrieval pipelines for VenSpec, with applications to both the Venusian atmosphere and surface. Second, it seeks to coordinate long-term monitoring of Venus’ atmosphere, including its dynamics and temporal variability, thereby bridging the observational gap between Akatsuki and EnVision and improving our understanding of global atmospheric behavior over the coming decade. Third, the group will encourage and organize ground-based observations during EnVision’s science phase from 2034 onward, providing valuable contextual information for measurements obtained by EnVision and VenSpec.

Our current activities include monitoring SO₂ abundances at the Venus cloud top using IRTF/TEXES (5–25 μm; spectral resolving power up to 80,000) [7]; conducting high-resolution spectroscopic observations of both the dayside and nightside with IRTF/iSHELL (1.1–5.3 μm; spectral resolving power up to 90,000) to study trace gases such as CO, H₂O, HDO, HF, OCS, SO₂, HCl, and H₂S [e.g., 8–10]; performing frequent multi-wavelength imaging with the Calar Alto telescope to investigate atmospheric dynamics through cloud morphology [11]; carrying out long-term monitoring of wind fields using Doppler shifts measured with high-resolution visible spectroscopy [12]; conducting high-spectral-resolution measurements with the High Dispersion Spectrograph at the Subaru Telescope (300–1000 nm; spectral resolving power up to 160,000) to search for molecular oxygen at the cloud top [13]; tracking the unknown absorber using ground-based spectropolarimetric measurements of Venus with NOT/ALFOSC (365–1015 nm); tracking the unknown absorber in the U band with STELLA [14]; developing an Earth-bound long-term CubeSat series, CLOVESat 1–5, planned for 2026–2042, to track the reflectivity of Venus [15]; and conducting long-term Venus monitoring with the Haleakala T60 telescope to investigate the unidentified UV absorber (300–500 nm). We also encourage collaboration with amateur astronomers. These activities will be summarized and presented in this contribution.

References

[1] Straume-Lindner, A. G., et al. 2025, EPSC-DPS Joint Meeting 2025, EPSC-DPS2025-850. [2] Helbert, J., et al. 2019, Proc. SPIE, 11128, 1112804, doi:10.1117/12.2529248. [3] Marcq, E., et al. 2025, EPSC-DPS Joint Meeting 2025, EPSC-DPS2025-395, doi:10.5194/epsc-dps2025-395. [4] Neefs et al. 2025 Acta Astronomica, 226. doi:10.1016/j.actaastro.2024.10.018. [5] Alemanno, G., et al. 2025, EPSC-DPS Joint Meeting 2025, EPSC-DPS2025-991, doi:10.5194/epsc-dps2025-991. [6] Hueso et al. 2025, EPSC-DPS2025-477, doi:10.5194/epsc-dps2025-477. [7] Encrenaz, T., et al. 2025, Astronomy & Astrophysics, 703, A219, 9. [8] Ferro-Milon, S., et al., this meeting. [9] Dias, J., et al., this meeting. [10] Sato T. M., et al. 2026, JPGU-AGU meeting 2026, PPS08-P03. [11] Sánchez-Lavega, A., et al. 2016, The Astrophysical Journal Letters, 833, L7 [12] Machado et al. 2014, Icarus, 243, 249–263. [13] Aoki, S, et al., this meeting. [14] Lee et al., 2022, Planet. Sci. J. 3 209. [15] Lee, Y. J. 2024, Europlanet Science Congress 2024, EPSC2024-158.