I got this error: An object reference is required to access non-static member

An object reference is required to access non-static member`UnityEngine.Component.rigidbody2D'

I don't understand! i Have to AlienMover script on my enemy with correct pronounciation using UnityEngine; using System.Collections;

 public class AlienDodge : MonoBehaviour 
 {
     public GameObject Alien;
     public float DodgeCoolDown = 0.5f;
 
     private float Force;
     private float dodgeCoolDown;
 
     void Start()
     {
         DodgeCoolDown = -1f;
         Force = Alien.GetComponent<AlienMover>().MaxForce;
     }
 
     void Update()
     {
         dodgeCoolDown = Time.deltaTime;
     }
 
     void OnTriggerEnter2D(Collider2D collider)
     {
         if (DodgeCoolDown < 0f)
         {
             AlienDodge.rigidbody2D.AddForce (Alien.rigidbody.velocity.normalized * ForceMode);
             dodgeCoolDown = DodgeCoolDown;
         }
     }
 }