C# Probability of Transform Colliding

Hi. I am trying to make two scripts. One below that is attached to an asteroid and moves it towards the target planet, and a second one to place on an observatory that would find the probability of the asteroid colliding with the target.

I know the script I have so far is completely wrong as the asteroid will always collide with the target every time. What I'm trying to do is get it to have a random probability of reaching the target and a second script that would calculate that probability. I am completely stuck and help to point me in the right direction would be much appreciated!!!

 using UnityEngine;
 using System.Collections;
 
 public class Asteroid : MonoBehaviour {
 
     public Transform target;
         //Planet
     public float speed;
         //Speed of Asteroid
 
     void Update() {
         float step = speed * Time.deltaTime;
         transform.position = Vector3.MoveTowards(transform.position, target.position, step);
     }
 
 void OnTriggerEnter(Collider other)
 {
     if (other.gameObject.tag == "Planet") {
             print ("Asteroid Impact");
             Destroy (gameObject);  
                         //Destroys Asteroid
         }
     }
 }