Black splotches when camera is far away

I’m having an issue with rendering a planet.
I followed the BlenderGuru tutorial here and have results that are far better than I could have hoped:

But in my scene, I have a camera that’s tracking a fireball pretty far away, and have zoomed in to keep the background earth visible.
Here’s a clip from the rendered scene:

When viewing in HD, you can see that there’s a weird black speckling covering the earth.
The Model, lighting, etc are all the exact same in the image and video. The only difference is that there is a second camera for the image.
Image camera:

  • Focal Length - 35
  • Clipping start - 0.1
  • Clipping end - 100.0
    Video camera:
  • Focal Length - 60
  • Clipping start - 0.001
  • Clipping end - 200.0

Any suggestions?
Thank you

It is z-fighting and happens because when objects are so far away, there’s only a very small difference in the z buffer. To fix, in BI at least, find the overlaying material (probably clouds?) and look in the materials tab for something like Z Offset. Change this value from 0 to something like 0.1 or so, see if that helps.

Thank you very much for your response.
I changed visibility between atmosphere and clouds, and it looks like it is the clouds material.
I increased that Z offset a few times but haven’t been able to solve the issue. Maybe I’d have to scale up the geometry for the clouds as well?
I think what I’ll do is just re-frame the shots with the earth in the foreground, since this was just a test render for the 2.65 fire simulation and the earth has far more detail than the comet anyway.

Now to fix the flames.