alpha mapped plane

i am trying to add 2 scenes together in blender. i have rendered a planet and its moon, and i have theie transparency map, i have applied that to a plane and in front of that is the asteroid which i wish to add into the scene.

the red background is so i could see if the transparency map worked or not, it didnt. you can see a red outline aroud the 3d asteroid mesh.

the planet needs to be on an alpha mapped plane because i need to move it for the animation so setting the image as the background wont work.

EDIT: fixed it by unchecking Z transparency and using ray transparency witn an ior of 1 instead