https://www.reddit.com/r/askscience/comments/14ld9uo/when_the_earth_loses_atmosphere_to_space_where/
created by seanalltogether on 28/06/2023 at 15:57 UTC
46 upvotes, 2 top-level comments (showing 2)
My understanding is that Earth loses a meaningful amount of gases into space every day, but where does it go? Does it keep going further and further until it falls into the gravity of another planet? Does it just hang out at a higher orbit from earth and just sit there forever? Does it get pulled back into earths gravity the next time earth comes back around?
Comment by Ausoge at 29/06/2023 at 03:51 UTC*
21 upvotes, 2 direct replies
As far as I understand it, much of it is carried off by solar wind. The sun is constantly shooting out a "wind" of charged particles in every direction, and light itself also does exert a non-zero force onto anything it hits. Planetary atmospheres can be completely blown away by this wind.
Mars is probably a good example of this - the jagged, grooved landscape of Mars is evidence of a much denser atmosphere having existed eons ago. There is considerable evidence of erosion by flowing gas and/or liquid - such erosion simply cannot happen without an atmosphere.
The advantage Earth has over Mars is that it is surrounded by a strong magnetic field driven by the solid iron core dynamo, which deflects/redirects most of that wind.
As for where the gases go, the atoms are pushed into orbit or carried off into interstellar space. Over a long time, they'll be gravitationally drawn to something like another star, planet, asteroid, or to each other.
Edit: I encourage everyone to read this whole reply thread. Lots of excellent information and corrections of misconceptions on how atmospheres are lost.
Comment by UpintheExosphere at 30/06/2023 at 10:36 UTC
1 upvotes, 0 direct replies
If they are ionized particles, they can have two fates if they escape down Earth's magnetic field tail or out of the polar regions: they can either become part of the solar wind, in what are called "pickup ions", or, some fraction of them will return back down the tail, called "return flow". The solar wind forms what is called the heliosphere, which stretches far out into interstellar space. Given how big the heliosphere is, and how small solar system bodies are relative to it, it's most likely the ions from Earth will just remain in the solar wind, not interacting with anything else.
Fun fact about pickup ions, we can actually observe interstellar pickup ions! As the heliosphere moves through interstellar gases, these interstellar particles can become ionized. We can tell where they are from based on their energy distribution and direction. Zirnstein et al., 2022[1]is a bit technical but the introduction summarizes this. Sometimes the opposite happens, where ions become neutralized, but still have high energies. These are called energetic neutral atoms, and are nice because unlike ions they travel in straight lines, so we can basically treat them like photons and use them to make an "image" of a magnetosphere. We have done this for the heliosphere (cool figures in McComas et al., 2011),[2] but also for various planets, including Earth (IMAGE mission, for one), Mars (Mars Express, for example), Saturn (MIMI on Cassini), etc etc etc (it's a very common instrument type and useful space physics data). So this is also something that can happen to escaping particles.
1: https://link.springer.com/article/10.1007/s11214-022-00895-2#Sec1
2: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011GL048763
Tl;dr they go out to space, where they just keep going.