How can I make an object invulnerable to collision with a specific object?

I am making a StarFox like game. In the game meteors are hurtling towards the characters ship, if the ship collides with a meteor the ships current health decrease. However, when I shoot the ships gun the bullets also collide and hurt the ship causing it to destroy itself. How can I make the ship invulnerable to the bullets but still take damage from the meteors?

Here is my code if it helps at all...this method is in a script for the ships attributes which declares the ships health and the amount of damage the ship takes from a collision.

 void OnCollisionEnter()
     {
         // Decreases our current health when hit by an object
         currentHealth = currentHealth - standardHit; //standardHit declares damage taken by collision
         
         // Tests if current health is less than 25
         if(currentHealth < 25)
         {
         // Writes to our debug log
         Debug.Log ("Your health is low!");
         }
         
         // Tests if current health is less than or equal to 0
         if(currentHealth <= 0)
         {
             // Destroys our game object
             Destroy(gameObject);    
         }        
     }