public float LandOnPlanet(Planet planet)
{
Vector3 direction = (this.transform.position - planet.transform.position).normalized;
float angle = Mathf.Acos(direction.x);
this.SetVelocity(0f);
this.SetAngle(angle);
this.SetPlanet(planet.gameObject);
planet.AddEntity(this);
return(angle);
}