The Venusian Atmospheric Oxygen Ion Escape: Extrapolation to the Early Solar System

Abstract

The present atmosphere of Venus contains almost no water, but recent measurements indicate that in its early history, Venus had an Earth‐like ocean. Understanding how the Venusian atmosphere evolved is important not only for Venus itself but also for understanding the evolution of other planetary atmospheres. In this study, we quantify the escape rates of oxygen ions from the present Venus to infer the past of the Venusian atmosphere. We show that an extrapolation of the current escape rates back in time leads to the total escape of 0.02–0.6 m of a global equivalent layer of water. This implies that the loss of ions to space, inferred from the present state, cannot account for the loss of an historical Earth‐like ocean. We find that the O+ escape rate increases with solar wind energy flux, where more energy available leads to a higher escape rate. Oppositely, the escape rate decreases slightly with increased extreme ultraviolet radiation (EUV) flux, though the small variation of EUV flux over the measured solar cycle may explain the weak dependency. These results indicate that there is not enough energy transferred from the solar wind to Venus' upper atmosphere that can lead to the escape of the atmosphere over the past 3.9 billion years. This means that the Venusian atmosphere did not have as much water in its atmosphere as previously assumed or the present‐day escape rates do not represent the historical escape rates at Venus. Otherwise, some other mechanisms have acted to more effectively remove the water from the Venusian atmosphere.

Venusian Habitable Climate Scenarios: Modeling Venus Through Time and Applications to Slowly Rotating Venus‐Like Exoplanets

“…For our Arid-Venus scenario, it may be possible to lose much of the oxygen via a combination of atmospheric escape (Persson et al, 2018) and absorption by a surface like that of present-day Venus (e.g., Gilmore et al, 2017). However, recently submitted work by Persson et al (2020) demonstrates that 0.3 m of a global equivalent layer of water could have been lost via atmospheric escape alone in the past ∼4 Ga. Hence, the 0.2 m global equivalent layer of water in our Arid-Venus scenario fits within this framework.…”

Depleted Plasma Densities in the Ionosphere of Venus Near Solar Minimum From Parker Solar Probe Observations of Upper Hybrid Resonance Emission

“…Without this flow, the main remaining source of ionization on the nightside is thought to be the precipitation of solar wind electrons (Gringauz et al, 1979), which is in general far less effective. Another potential explanation can be inferred from the Venus Express studies by Kollmann et al (2016), Masunaga et al (2019), andPersson et al (2020), that tailward ion escape rates are higher during solar minimum, effectively depleting the nightside ionosphere. The Parker Solar Probe observations presented here are compatible with both of these hypotheses.…”

Evolution of the Earth's Polar Outflow From Mid‐Archean to Present

“…Recent results indicate that an intrinsic magnetic field has been possible also on ancient Venus (O'Rourke et al., 2018). Current escape rate of oxygen from Venus, if extrapolated into the past, could have removed 0.02–0.6 m of a global equivalent of water (Persson et al., 2020). However, if Venus indeed has had a magnetic field in the past, then a dominant escape mechanism was likely different than today, which would change the picture of its atmospheric evolution.…”