Prospective Venus Cloud trace species detectability as inferred from Hubble

The composition and chemical processing occurring within the Venus atmosphere is derived by a combination of direct observation (both in-situ and remote) and chemical and climate modeling (Widemann et al. 2024, Marcq et al. 2018). Chemical modeling and atmospheric properties retrievals from observations are interdependent efforts. Venus’s bulk atmosphere is composed of CO₂ (96.5%) and N₂ (3.5%), while SO₂ (~0.015%), Argon (0.007%) and water (0.002%) round out the top 5 gas species present in the Venus atmosphere. Observations and chemical modeling indicate that Venus's clouds also host a myriad of sulfur, oxygen, nitrogen, hydrogen, chlorine, carbon and oxygen trace gas species. While it is understood that the Venus clouds are dominantly composed of H₂SO₄ aerosol, and that the H₂SO₄ gas within the atmosphere is formed by chain reaction of SO₂ photolysis leading to formation of SO₃ and the interaction of SO₃ with H₂O—many questions remain about what controls the abundance of H₂SO₄, H₂O and SO₂ in the Venus atmosphere (Marcq et al. 2018, Bierson et al. 2020, Rimmer et al. 2021, Dai et al. 2022). Unequivocal answers to these questions are dependent on how precisely we can identify and quantify the other trace gas and aerosol forming species present in the atmosphere and their propensity to interact with Venus’s sulfur, oxygen and water budgets.  (Mogul et al. 2021, Rimmer et al. 2021, Jiang et al. 2023, Jessup et al. 2020)

Progress in resolving these questions is being made as chemical and climate modeling become increasingly sophisticated (Stolenzbach et al. 2023, Dai et al. 2022, Dai et al. 2024). Likewise, efforts to advance and improve lab and theoretical studies of the physical properties of gases and aerosols that may be present in the Venus atmosphere are on-going (Frandsen et al. 2024, Skog et al. 2024, Jiang et al. 2023, Heays et al. 2017 Heays et al. 2023). These advances and the anticipation of several new Venus missions, motivates the review/re-analysis of several previously obtained remote/in-situ datasets (Mogul et al. 2021, Mahieux et al. 2024, Mahieux et al. 2023, Lincowski et al. 2021). As a result, several sulfur-based species previously not conclusively observed have now been definitively detected within remote sensing data (Mahieux et al. 2023), while debate rages on about species detected via in situ observation opportunities (Lincowski et al. 2021, Mogul et al. 2021).

 

Several gases recently positively detected by SOIR have absorption at UV wavelengths coincident with previously obtained Hubble Space Telescope spectra (Jessup et al. 2015, Jessup et al. 2020). We present a summary of the detectability of these species in the previously obtained Hubble data. We discuss what these and the recent SOIR retrievals may mean for anticipated monitoring of the Venus cloud top and middle atmosphere at UV and other wavelengths via the EnVision/VenSpec instrument (Marcq et al. 2021). We also discuss to what extent the detectability of these species at UV wavelengths impacts open controversial in-situ detections (Mogul et al. 2021); especially those that may directly impact the sulfur cycle or other cloud level atmospheric constituents (Rimmer et al. 2021).

 

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