Random Object Spawning

Hello im trying to spawn two Objects but i get a error "NullReferenceException: Object reference not set to an instance of an object" I know what that means but i cant find my error. The error marks me sometimes the first transform(marked) and sometimes the second. It looks like that he have problems to spawn the second object after the first object was already spawned.

public class PlanetSpawner : MonoBehaviour {

 //Planeten
 public GameObject Planet1;
 public GameObject Planet2;
 private int momentanerPlanet = 0;
 //Planten-Klons
 private GameObject[] CPlanet1;
 private GameObject[] CPlanet2;
 //Random
 private int Planetchoser;
 //Settings
 public int MaxPlanets = 5;
 public float minSpawn = -1f;
 public float maxSpawn = 3.5f;
 public float spawnRate = 4f;
 private Vector2 PlanetPosition = new Vector2(-15f, -25f);
 private float timeRespawn;
 //Spawn Positions
 private float spawnXPosition = 10f;
 // Use this for initialization
 void Start() {
     CPlanet1 = new GameObject[MaxPlanets];
     CPlanet2 = new GameObject[MaxPlanets];
 
  for(int i = 0; i < MaxPlanets; i++)
  {
         Planetchoser = Random.Range(0, 7);
         if(Planetchoser < 3 )
         {
             CPlanet1[i] = (GameObject)Instantiate(Planet1, PlanetPosition, Quaternion.identity);
            
         }
         else if(Planetchoser > 3)
         {
             CPlanet2[i] = (GameObject)Instantiate(Planet2, PlanetPosition, Quaternion.identity);
             
         }
         Debug.Log(Planetchoser);
  }
 }

 // Update is called once per frame
 void Update()
 {
     timeRespawn += Time.deltaTime;

     if (MainContol.instance.gameOver == false && timeRespawn >= spawnRate)
     {

         {
             timeRespawn = 0;
             float YPosition = Random.Range(minSpawn, maxSpawn);
             if(Planetchoser < 3)
             {
                  //the Error appears here
                 CPlanet1[momentanerPlanet].transform.position = new Vector2(spawnXPosition, YPosition);
                 momentanerPlanet++;
                 Debug.Log("Planet1");
             }
             else if(Planetchoser > 3)
             {
             // or the error appears here
                 CPlanet2[momentanerPlanet].transform.position = new Vector2(spawnXPosition, YPosition);
                 momentanerPlanet++;
                 Debug.Log("Planet2");
             }
             if( momentanerPlanet >= MaxPlanets)
             {
                 momentanerPlanet = 0;
             }
         }
     }
 }

} I trying it for a while now so i hope you can help me