Raycast Object Selection

First, do you have just the one camera? If you have two cameras, you might want to use a reference to the camera inside your script instead of Camera.main (in general you might want to use it for performance benefits).

Second, I can recommend a perhaps simpler way to handle clicks on items: OnMouseUpAsButton. T$$anonymous$$s method is invoked in any MonoBehaviour attached to an object that is clicked - meaning button is pressed and released on top of the object (as long as the object has a collider). You also have OnMouseDown to handle button pressed (without releasing), OnMouseDrag to handle holding the button down, OnMouseUp, etc.

Now, I would create a simple script that detects clicks on an object, and calls a method on your HUD script:

public class MapHud : MonoBehaviour { // all your code here

 // handle clicks on objects
 public void ObjectClicked(ClickableObject obj) {
     Debug.Log("selecting");
     DeselectPlanet(); // deselect previous target (if any)...
     selectedPlanet = obj.transform; // set the new one...
     planetselect(); // and select it
 }

}

public class ClickableObject : MonoBehaviour { private MapHud hud;

 public void Start() {
     hud = Object.FindObjectOfType(typeof(MapHud)) as MapHud;
 }

 public void OnMouseUpAsButton() {
     hud.ObjectClicked(t$$anonymous$$s);
 }

}

Then simply attach the ClickableObject script to any object you want selectable. Remember to make sure they all have colliders. In t$$anonymous$$s case it doesn't matter how many cameras you have.