How to realistically add planet in the sky using 3d camera tracker and avoid overlapping with objects in the foreground?
If the blades are rotating, and the camera is moving, you need to create a good foreground layer with anything the planet is supposed to be obscured by.
So from the image it looks like it will be obscured by the spinning rotors.
You need to find a good way to make a layer containing only the rotors.
You could make a mask and move it frame by frame, but if you have more than a few frames this method will take a long time.
You could try using a key - isolating your foreground based on hue (colour), brightness or saturation (how much colour is present).  The blades look like the whitest thing in the image, so this might work, but probably won't give you the result you're looking for...
Or you could rotoscope the blades.  This will take a while, but will probably give the best result. The new rotoscope v2 in the latest versions of After Effects is really amazing, and combined with some careful feathering / motion blur settings will probably work perfectly.  It will still take a while though.
To get the planet in the right position in the sky, you need to make a camera track of the scene, then place the planet as a 3D layer at the right distance and scale.