7 research outputs found
The long-term evolution of the atmosphere of Venus: processes and feedback mechanisms
In this chapter, we focus on the long-term evolution of the atmosphere of
Venus, and how it has been affected by interior/exterior cycles. The formation
and evolution of Venus's atmosphere, leading to the present-day surface
conditions, remain hotly debated and involve questions that tie into many
disciplines. Here, we explore the mechanisms that 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 fundamental processes such
as volcanic outgassing, surface-atmosphere interactions, and atmosphere escape.
Furthermore, we address more complex aspects of the history of Venus, including
the role of meteoritic impacts, how magnetic field generation is tied into
long-term evolution, and the implications of feedback cycles for atmospheric
evolution. Finally, we highlight three plausible end-member evolutionary
pathways that Venus might have followed, from the accretion to its present-day
state, based on current modeling and observations. In a first scenario, the
planet was desiccated early-on, during the magma ocean phase, by atmospheric
escape. 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 needed to refine our understanding of the planet's
history and of the complex feedback cycles between the interior, surface, and
atmosphere that operate in the past, present or future of Venus
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Early Habitability and Crustal Decarbonation of a Stagnant-Lid Venus
Little is known about the early evolution of Venus and a potential habitable period during the first 1 billion years. In particular, it remains unclear whether or not plate tectonics and an active carbonate-silicate cycle were present. In the presence of liquid water but without plate tectonics, weathering would have been limited to freshly produced basaltic crust, with an early carbon cycle restricted to the crust and atmosphere. With the evaporation of surface water, weathering would cease. With ongoing volcanism, carbonate sediments would be buried and sink downwards. Thereby, carbonates would heat up until they become unstable and the crust would become depleted in carbonates. With CO2 supply to the atmosphere the surface temperature rises further, the depth below which decarbonation occurs decreases, causing the release of even more CO2. We assess the habitable period of an early stagnant-lid Venus by employing a coupled interior-atmosphere evolution model accounting for CO2 degassing, weathering, carbonate burial, and crustal decarbonation. We find that if initial surface conditions allow for liquid water, weathering can keep the planet habitable for up to 900 Myr, followed by evaporation of water and rapid crustal carbonate depletion. For the atmospheric CO2 of stagnant-lid exoplanets, we predict a bimodal distribution, depending on whether or not these planets experienced a runaway greenhouse in their history. Planets with high atmospheric CO2 could be associated with crustal carbonate depletion as a consequence of a runaway greenhouse, whereas planets with low atmospheric CO2 would indicate active silicate weathering and thereby a habitable climate
The long-term evolution of the atmosphere of Venus: processes and feedback mechanisms
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 and 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