Asteroid
An Asteroid is a small, immobile, natural mass of stone voxels in the game's space environment. They typically occur in clusters and despite their variety of sizes, they are too small to exert any natural gravity on grids or players.
Gallery
A generic asteroid
An example of an asteroid base from the Sparks of the Future scenario
Tiny static asteroid rocks pose a danger to fast flying ships
Resources
In addition to ubiquitous stone, some asteroids contain lucrative deep veins of Ores that you can mine with drills. Each asteroid may contain two or more types of ore, with ice also included as an "ore". In unmodded games ("vanilla"), they can contain all types of ore that are available in the game. Especially Uranium Ore is found only in asteroids and very valuable.
How to change asteroid density
Worlds in Space Engineers are infinite and filled with procedurally-generated[1] asteroid clusters as needed.
You can adjust the asteroid amount in the World Settings but only before you start the game for the first time. You can choose between high and low density; the default setting is called "normal density".
How do asteroids spawn
Asteroids only spawn when players are near, this means that an exploration drone cannot trigger their generation.
It's recommended to start mining a bit of any valuable ore that you find before you fly far away, because it is possible that unmodified asteroids (and their deposits) are regenerated differently after your return.
Building on asteroids
In Survival Mode, asteroids are a relatively protected place where you can build space bases, either inside of, or attached to, the asteroid’s voxels. For related options, see also "Unsupported Stations" in the World Settings.
In Creative Mode, you can shape and edit asteroids and the ores on them (other than by drilling), for details, see Voxel Hands. You can add asteroids yourself, for example when creating a custom scenario; just use the same method as for How to Spawn Planets and Moons Manually, but select Asteroids instead. Then paint ore materials on them using Voxel hands.