This really interests me as well - how do they know that it's a 12 million years old planet?

I suppose a big reason would be that it does give off a heat significant (if not AS significant) signature to begin with - a large spaceship would very likely try to conserve as close to 100% of its energy.

Then again - what about a dyson sphere that is still under construction?

Berserker

Space hulk!

Maybe it's Jenova's?