new-horizons/docs/content/pages/api.md

Title: API Sort-Priority: 40

How to use New Horizons in Other Mods

First create the following interface in your mod:

public interface INewHorizons
{
    void Create(Dictionary<string, object> config, IModBehaviour mod);

    void LoadConfigs(IModBehaviour mod);

    GameObject GetPlanet(string name);
}

In your main ModBehaviour class you can get the NewHorizons API like so:

public class MyMod : ModBehaviour 
{
    void Start() 
    {
        INewHorizons NewHorizonsAPI = ModHelper.Interaction.GetModApi<INewHorizons>("xen.NewHorizons");
    }
}

You can then use the APIs LoadConfigs() method to load from a "planets" folder, or use the Create() and GetPlanet methods to create planets and do whatever with them. Just make sure you create planets in the Start() method or at least before the SolarSystem scene loads, or they will not be created.