P049-01
The Venusian Atmospheric Ion Escape and its Effect on the Atmospheric Evolution

Friday, 11 December 2020: 05:30
Virtual
Moa Persson1, Yoshifumi Futaana2, Hans Nilsson2, Robin Ramstad3, Andrei Fedorov4, Stanislav V Barabash5 and Janet G Luhmann6, (1)Swedish Institute of Space Physics, Kiruna, Sweden, (2)IRF Swedish Institute of Space Physics Kiruna, Kiruna, Sweden, (3)Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, CO, United States, (4)IRAP, CNRS, Toulouse, France, (5)Swedish Inst Space Physics, Kiruna, Sweden, (6)University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, United States
Recorded Presentation
Abstract:
Today, the Venusian atmosphere is massive, and contains only a small amount of water. However, measurements indicate that in its early history the atmosphere contained a significant amount of water. The water can be removed through several processes, where one of the main channels is a consequence of the interaction between the ionosphere and the solar wind. As the solar wind flows past Venus, some of its energy and momentum are transferred to the upper atmospheric ions. The additional momentum allows the ions to reach above escape velocity and escape the planet. Therefore, the upstream solar wind is important to consider for the evolution of the Venusian atmosphere.

Using measurements from Venus Express we have found the present day relation between the escape rates and the upstream solar wind. The results show that an increase in the amount of energy available in the upstream solar wind increases the total escape rates of oxygen ions. However, the increase is not linear; As the available upstream energy increases, a smaller fraction of the energy is transferred to the escaping ions. The found relation is used to extrapolate backwards in time to find the historical escape rates from Venus. The simple extrapolation, using the current relation between the solar wind and the escape rates together with the evolution of the solar wind, show that in total a global water layer depth of 0.02-0.6 m have been removed by ion escape. This is a significantly smaller water depth than the expected of several hundreds of meters. However, the found water layer depth lost to space may have been modulated by the effect of extreme space weather events, which was more frequent in the early history of the solar system and can cause an increase in the escape rates.

In this talk we will summarize the results of the escape rates and its relation with the upstream solar wind from measurements by Venus Express. The results will be put into context of both previous escape studies by the Pioneer Venus Orbiter and the potential effects from extreme space weather events. Lastly, we will discuss further measurements or studies needed in order to further constrain the effects of the solar wind on the Venusian atmospheric evolution.

Previous Abstract | Next Abstract >>