I am currently writing a story that involves the never-ending-theme of alien invasions. Assume Humans are roughly at a Type I civilization at this point. Humans have unfortunately wandered into a middle of a galactic battle, and because we always make great decisions, we chose a side to join, let's say the Galactic Empire.
The other side, the First Order, is not very happy about this and decides to completely annihilate Earth. Their planet-destroying weapon is going to lock on Earth and destroy it. However, its preparation time is long and needs a very accurate lock-on of the target. Therefore, in defense, Earth has came up of the idea of a Decoy Earth:
- The Decoy Earth would be an obloid spheroid in the same dimensions and the shape of the Earth, except that it is actually completely hollow and only consists of surface light emitting panels.
- The Decoy Earth would be placed on the Earth Orbit at the point directly opposite the current Earth, and be given a rotational velocity exactly equal to that of Earth's, so that the two Earths are always directly opposite each other.
- The light emitting panels of the Decoy Earth emit light of the same spectrum as the true Earth.
The purpose of the Decoy Earth is for the First Order to not know which Earth is the real one and thus have a $1/2$ chance of locking on the wrong planet. Assuming the weapon takes an extremely long time to recharge, this would give humans more breathing time for us to figure out a plan.
Now my questions are:
- How well can this Decoy Earth actually serve as a Decoy from distances of $\sim 1000$ light years? From my (very basic) understanding of astrophysics, the Decoy Earth would seem to do pretty well under direct imaging and the transit method. Clearly the mass of the two objects are vastly different, so gravitational microlensing can potentially reveal the truth, but is microlensing capable of discovering Earth-like planets at that distance?
- (Optional) What would be the minimal distance in which this Decoy is effective, assuming current human technology in telescopes? You are welcome to assume that all current telescopes in full construction (e.g. JWST) as usable.