If space is a vacuum and has no resistance, what force are the solar winds ccoming up against to create the heliosphere/heliopause?
Edit: spelling because im my own worst enemy.
In: 3
Space is not 100% vacuum, actually. The solar system is in the Milky Way galaxy, and it’s rotating around the center of it and through the various (thin) [gases within the galaxy](https://solarsystem.nasa.gov/internal_resources/125/). In addition, the Sun emits plasma (the solar wind), and stars nearby (Proxima, Alpha Centauri for example) also emit their solar winds, and these winds “clash”.
The [wiki article](https://en.wikipedia.org/wiki/Heliosphere) explains it in detail.
It’s a vacuum, but not a *perfect* vacuum. The farther the solar wind gets from the Sun, the more it’s spread out, and eventually it’s of density comparable to the interstellar medium.
> In the interstellar medium, matter … reaches number densities of 10^6 molecules per cm^3 (1 million molecules per cm^(3)). … Compare this with a number density of roughly … 10^10 molecules per cm^3 (10 billion molecules per cm^(3)) for a laboratory high-vacuum chamber.
https://en.wikipedia.org/wiki/Interstellar_medium
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