Prevent instantiating on collider


I make a game where planets generate automaticly. There is a problem that sometimes they generate touching an other one.
How can I destroy the previous planet if a new one instantiate on it? Like removing the old for the new planet. Thanks!

I use a prefab for the planet

You could try something like this:

   // in your "planet" script
    var dateOfBirth : float;
    function Start() {
       dateOfBirth = Time.timeSinceLevelLoad;
    function OnCollisionEnter(other) {
       otherPlanet = other.gameObject.GetComponent("planet");
       if (otherPlanet && otherPlanet.dateOfBirth < dateOfBirth) {