4 upvotes, 1 direct replies (showing 1)
It is! Venus experiences constant escape of both ions and neutral atmosphere components. Venus does lose oxygen as well (see Persson et al., 2020[1] for a relatively recent paper). Venus just has such an enormous atmosphere that it doesn't really make a difference. Also, Venus has what is called an 'induced' magnetosphere, where currents in the ionosphere stave off the solar wind, and this effectively protects it as well.
1: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006336
The exact escape rates from Venus, Earth, and Mars are difficult to measure and require a lot of interpolation, so estimates vary pretty widely, but depending on the method of atmospheric escape, it can be actually quite similar between the three. For example, the rate of ion escape from Earth is fairly close to, and maybe even higher than, the ion escape rate at Venus.
The poster who mentioned hydrogen is referring to a specific type of escape called Jeans escape, which is where a particle's thermal energy (can happen for both neutrals and ions) is higher than the gravitational escape energy. For neutrals, you can also get escape from ions, like for example from the solar wind, hitting them and giving them energy like a billiard ball collision and knocking them out into space; this is called sputtering. For ions at Venus, which are directly exposed to the solar wind, the solar wind magnetic field can "pick them up", so they start following that and leave the atmosphere. At Earth, ions will follow the magnetic field lines out into the deep magnetotail on the night side or up at the polar regions, which they can then escape from. These extra ion escape channels are why ion escape rates at Earth are similar(-ish) to those at Venus. Gunnell et al., 2018[2] goes into this, as well as other papers that aren't open access.
2: https://www.aanda.org/articles/aa/full_html/2018/06/aa32934-18/aa32934-18.html
Basically, tl;dr, escape happens at Earth too, but compared to the global mass of the atmosphere it's such a small fraction that you only see changes over billions of years. Plus, Venus is possibly still outgassing from volcanic activity (not a geologist, so not positive on this) so it's possible it's replenishing its atmosphere.
Comment by Bravemount at 30/06/2023 at 12:57 UTC
2 upvotes, 0 direct replies
Thanks for the detailed explanation.
From a quick look at Wikipedia, it would seem that Venus is the most volcanically active planet in the solar system, so probably doing enough outgassing to compensate.
Also, as a language nerd, let me add that the Geology of Venus should logically be called Aphrodoloy. However, a quick Google search will illustrate why that term is much less successful than Areology (the study of Mars): you'll find plenty of beauty products and armchair relationship/sex advice if you search for Aphrodology (and variants thereof). Probably not something academics want to be confused with.