I understand that astronomers cannot yet detect extra-solar earth-like planets. However, I’m finalizing details on a science fiction story (about an astronomer) set 200 years in the future. It assumes regular scientific and human advancement – it’s not dystopian. But there is NO faster than light travel (sorry trekkies). Anyhow, assume there’s a solar system similar to ours. The system’s “Earth2” is similar in size, composition, & distance from its star as Earth is to the sun. “Earth2” also has a biosphere and atmosphere similar to an Earth – but no intelligent life. Earth2's star is similar to the Sun. Will we be able to detect “Earth2” and its bio-atmosphere in the near future (~50 years) out to distances of 50 light years? 70 ly? 100 ly? In the far future of my story (200+ years out), I assume a large space based array-detection system could detect such an Earth2 and its bio-atmosphere out to 50 ly. Is that reasonable? Is it reasonable out to larger distances? Is there a theoretical limit to how distant an Earth2 can be passively detected? Could a sufficiently advanced civilization passively ‘map’ life bearing planets within its local tenth of the galaxy? Or a quarter of the galaxy?