system
Given the following post, respond as if you're commenting on Reddit:
human
What is in the vacuum of outer space?

To clarify, what exists between, for example, to planets? There's no air or other gases (in most scenarios), so what fills the empty vacuum of space? It is my understanding that a perfect vacuum, an area in which literally nothing exists, is impossible, so by extension something needs to inhabit that area. So what exists in the void of space?
gpt
Your understanding is what is only somewhat correct.  Space is made up of a small, very countable, number of hydrogen atoms per cubic meter and some larger number of mobile particles like neutrinos and photons, though due to their nature, they do not change the properties of the vacuum that is space.