## Overview

In gameplay, every planet has a **circle of influence** (hereafter referred to as **COI**), which is the circular area containing it. This is bounded by a grey circle centered on the planet, and any Object that crosses into the circle is subject to the gravity of the planet.

A spacecraft, space station, or some other Object achieves a stable orbit if it has sufficient velocity (indicated by a *brightened green section* of the velocity gauge). The Object "falls" towards the planet if the velocity is too low (i.e., only the *orange section* of the velocity gauge is lit). It leaves orbit following the *red exit line* if the velocity of the Object is greater than the escape velocity (represented by the marking *between the red and green sections* of the velocity gauge) of the planet. On the other hand, if the velocity gauge moves into the *red, *attempting to enter orbit causes the Object to perform a slingshot maneuver; that is, it gains speed for some time, slows down, and escapes the COI facing a different direction.

In missions you can find a white circle around a station. It is not a circle of influence, but a line, which will give you a failure if you will take the station from it.

## Trivia

- Technically, the circle defining the boundary of a COI isn't a (perfect) circle but a regular polygon.
- In reality, the magnitude of the gravitational pull of a planetary body is proportional to distance. This is difficult to portray in game mechanics, so every planet is simply depicted having a COI in-game.
- In astronomy, "sphere of influence" describes it well (but not in terms of mathematics).
- In the generality of physics, the greater the mass of a planet, the stronger the gravity of that planet is; therefore, the farther its gravity affects, e.g., the gravitational field of Jupiter is clearly stronger and larger than that of the Moon.