Duplicate Earth and Moon, where should I put it?
This question partly arises from the criticisms of stories that claim a hidden planet obscured by the sun, how it would have been detected and if sharing earths orbit it would eventually approach earth, potentially wreaking havoc.
Interactions with other planets slows/speeds one more than the other and they collide. This all arises from the debunking of other stories and mythologies claiming there is another earth in exact orbit but other side of sun. Well that is said to be impossible. Would have been detected by many means. That concept is fairly well covered here. https://www.youtube.com/watch?v=U-P_EjZKbaM
I am NOT claiming there is a duplicate Earth in our orbit hiding behind the sun. But I am considering scifi-magically creating one and I'm wondering in what sort of orbit I would place it in our solar system, how long it would be before it would threaten disaster and potentially collide with earth. I mean if that's 5 billion years away when the sun turns red giant...
I realize it would not be a stable orbit in relation to earth (What would you call an orbit that remains roughly 180 degrees away aside from variances caused by elliptical orbit?) A half year away. How long before the gravity of passing objects such as Venus, Jupiter and Mars makes a duplicate earth collision possible?
Would it be a less disaster prone situation if instead of second-earth sharing the same orbital path, it's elliptical orbit was 90 degrees out of phase and tilted? Where best to locate the dual planet (with moon)?