2022, Gillmann, Cedric, Way, M. J., Avice, Guillaume, Breuer, Doris, Golabek, Gregor J., Höning, Dennis, Krissansen-Totton, Joshua, Lammer, Helmut, O’Rourke, Joseph G., Persson, Moa, Plesa, Ana-Catalina, Salvador, Arnaud, Scherf, Manuel, Zolotov, Mikhail Y.

This work reviews the long-term evolution of the atmosphere of Venus, and modulation of its composition by interior/exterior cycling. The formation and evolution of Venus’s atmosphere, leading to contemporary surface conditions, remain hotly debated topics, and involve questions that tie into many disciplines. We explore these various inter-related mechanisms which shaped the evolution of the atmosphere, starting with the volatile sources and sinks. Going from the deep interior to the top of the atmosphere, we describe volcanic outgassing, surface-atmosphere interactions, and atmosphere escape. Furthermore, we address more complex aspects of the history of Venus, including the role of Late Accretion impacts, how magnetic field generation is tied into long-term evolution, and the implications of geochemical and geodynamical feedback cycles for atmospheric evolution. We highlight plausible end-member evolutionary pathways that Venus could have followed, from accretion to its present-day state, based on modeling and observations. In a first scenario, the planet was desiccated by atmospheric escape during the magma ocean phase. In a second scenario, Venus could have harbored surface liquid water for long periods of time, until its temperate climate was destabilized and it entered a runaway greenhouse phase. In a third scenario, Venus’s inefficient outgassing could have kept water inside the planet, where hydrogen was trapped in the core and the mantle was oxidized. We discuss existing evidence and future observations/missions required to refine our understanding of the planet’s history and of the complex feedback cycles between the interior, surface, and atmosphere that have been operating in the past, present or future of Venus.

2022, Lee, Yeon Joo, García Muñoz, Antonio, Yamazaki, Atsushi, Quémerais, Eric, Mottola, Stefano, Hellmich, Stephan, Granzer, Thomas, Bergond, Gilles, Roth, Martin, Gallego-Cano, Eulalia, Chaufray, Jean-Yves, Robidel, Rozenn, Murakami, Go, Masunaga, Kei, Kaplan, Murat, Erece, Orhan, Hueso, Ricardo, Kabáth, Petr, Špoková, Magdaléna, Sánchez-Lavega, Agustín, Kim, Myung-Jin, Mangano, Valeria, Jessup, Kandis-Lea, Widemann, Thomas, Sugiyama, Ko-ichiro, Watanabe, Shigeto, Yamada, Manabu, Satoh, Takehiko, Nakamura, Masato, Imai, Masataka, Cabrera, Juan

We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns.