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);	
		}		
	}

go to Edit/Project Settings/Physics you will then see Layer Collision Matrix in inspector panel.
Give ship a different layer to missile / bullet. untick relevant box’s in the matrix.