You can use Terrain:CopyRegion to achieve so. Description:- Stores a chunk of terrain into a TerrainRegion object so it can be loaded back later. Note: TerrainRegion data does not replicate between server and client.
The params are only one, which is Region3int16. It’s like the complex version o fhttps://developer.roblox.com/en-us/api-reference/datatype/Region3
Wait a a minute, so are the asteroids made of terrain?