The Long-Term Evolution of the Atmosphere of Venus: Processes and Feedback Mechanisms

Abstract

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.

Noble Gases and Stable Isotopes Track the Origin and Early Evolution of the Venus Atmosphere

“…This estimate for the amount of degassed radiogenic argon is about half the value estimated for Earth (Allègre et al 1987). Note that estimates for the total outgassing of 40 Ar over Venus's history strongly rely on the assumed K/U ratio for bulk Venus, which remains debated (see the discussions by Lammer et al (2020) and by Gillmann et al (2022)). Limited outgassing of radiogenic Ar over 4.56 Ga is the basis for the common view that Venus remained quiescent, in a stagnant-lid tectonic regime, during most of its history (O'Rourke and Korenaga 2015).…”

“…It is of vital importance to understand the role of mantle outgassing in shaping surface conditions on Venus (Gillmann et al 2022). Identification of radiogenic 129 Xe excesses in the atmosphere of Venus would suggest that at least some portion of the interior experienced early degassing to fractionate I/Xe during the lifetime of 129 I, and has subsequently outgassed to affect the Venus atmospheric composition.…”

“…Although many of the scientific questions raised in Section 3 could be, at least partially, answered with an in-situ sampling and characterization mission, returning an atmospheric sample from Venus would bring the scientific output of any mission to Venus to another level. For example, determination of the ∆ 15 N 15 N value of Venus atmospheric nitrogen, which quantifies the excess in the 15 N 15 N molecule relative to a random distribution of N atoms in N 2 , would allow to investigate the photochemistry of atmospheric nitrogen on Venus and to evaluate the amount of exchanges between Venus interior and its atmosphere (Yeung et al, 2017;Labidi et al, 2020;Gillmann et al, 2022). Similarly, applying very sensitive isotope determination techniques to a sample from the Venus atmosphere would allow detection and precise measurement of the abundances of minor isotopes of noble gases ( 3 He but also 78 Kr and 124,126 Xe) in order to better evaluate the delivered mix of volatile elements to the Venus atmosphere but also to put constraints on atmospheric escape processes or on interior-surface interactions.…”

“…This chapter presents an overview of the current state of knowledge and the outlook for future discoveries brought from the study of noble gases and of stable isotopes of C, H, O, N and S regarding the origin and early evolution of the atmosphere of Venus and on the implications for the geological history of the entire planet. Note that other contributions in this journal will cover in detail the role of water in Venus's history (Salvador et al 2022) and the complex interactions between the interior and the surface of Venus (Gillmann et al 2022).…”

The Habitability of Venus and a Comparison to Early Earth

“…Additionnally, the specifics of the regime may depend on the history of the planet (for instance Weller et al, 2015;Weller and Kiefer, 2020) and in particular the transition between the magma ocean solidification and the solid mantle convection (see Salvador et al, 2017Salvador et al, , 2022. This topic is discussed further in (Gillmann et al, 2022;Rolf et al, 2022, this issue).…”