TLDR at the bottom
Skeld is the main spaceship of the space organization that is being attacked by imposter aliens who are trying to end the organization that recently took possession of their home planet (more on later), as they are in a spaceship, when a person is ejected it is thrown into space. If that is not enough proof for you about being a ship, we can use as a proof the weapon system that has your cannons out, possibly to attack enemy ships and also asteroids (as we see in the task) as well as navigation (to navigate the ship, very self-explanatory name)
Mira HQ takes place in a building, proof of that is the animation that is shown when someone is ejected, of someone being thrown from the top of that building and falling to their death. As the name suggests, HQ stands for Head Quarter (duh). It is probably the headquarters of such an organization that by the name of the map we can assume that it is Mira. Evidence that this is actually the headquarters includes: Remote maintenance of the ship (task located on the map spawn) and also the laboratory, where they must do research on the planet and the species of the imposters.
Polus takes place at Mira's base on the planet of impostors! This can be confirmed by the spawn, where it seems that the ship we spent time waiting for the game to start finally landed and opened its door. The atmosphere and the geography of the place is pretty odd, like the purple floor and the lava pit in the middle of the terrain (where those that are ejected are thrown). Regarding the places that prove this theory, we have the weapons (to shoot possible threats and asteroids that circulate the planet) and the specimen room, where Mira's crew must keep artifacts and small species from the home planet of the imposters for study. About tasks, we have the drill task on the right of the spawn, probably the organization invaded this planet for mining (which would also explain the crystal task in Mira), and also the tree tasks (they must need it to maintain oxygen, since the atmosphere of this planet is different) and the temperature regulation. Regarding the Polus vents, we can see that they are actually holes, since they are made in the ground and not in a man-made structure. BThese holes can either be made by the drill I mentioned, just part of the terrain, or maybe they are tunnels built by imposters. Impostors are possibly a species that lives in tunnels. This would explain the holes in Polus and why the surface was so smooth and perfect to build, because who lived there didn't use the surface. However, with the drill being installed, their home is at risk, which is perhaps why they want to end Mira's exploration. To further confirm this, we can use as an example of the fact that only impostors can use vents and holes, because they have a much greater aptitude than the crew, since they have always lived in tunnels and systems of this kind. They can also see in the dark (as we know mainly by the light sabotage). Maybe that's why the crew members don't use vents, in Polus because they know they are in danger of possibly crashing into a colony of imposters and in Mira HQ and Skeld because they don't see in the dark of the vents and also because they can run into an imposter in there!
This really brings a different perspective on the game. Where Mira's organization seized by greed invaded a planet to exploit its natural resources, but it took a blow back from the inhabitants of that planet who can infiltrate perfectly with the crew. Now Mira's workers must be concerned not to be attacked by hostile locations in Polus, by imposters trying to take control of the ship in Skeld, and by crafty aliens trying to take control of the company in Mira HQ to save their people and their planet.
TLDR: Mira is a company that is using the impostor's home planet to mine and get resources and they are invading their crew to seek revenge
Source: https://www.reddit.com/r/AmongUs/comments/kb7bom/among_us_lore_theory_that_i_made_and_need_to_post/