A standard element of science fiction stories and movies is colonies on other worlds. In reality, of course, no planet in the Solar System is habitable and planets in other star systems that seem like they might be habitable are way too far to get to using current technology.
But what if there were an Earth-like planet in our Solar System? Imagine, for instance, another planet of about the same size and composition and with a breathable atmosphere in the same orbit. What if it’s exactly opposite us, so that if you picture Earth’s orbit as a clock, when Earth is at twelve, the other planet is at six. That would put the planet at about 186 million miles away.
Do we have the technology today to colonize it on a large scale? If not now, how soon could we do so?
And if this planet was directly opposite Earth, it would never be directly visible, since it would always be behind the Sun. So when, if ever, would we discover it? Would its impact on the orbits of the other planets lead to its assumed existence? Would it be visible in photos taken by an interplanetary probe (like the famous Pale Blue Dot photo taken by Voyager 1)?