How close would Earth and Mars have to be at conjunction to significantly affect each other's orbits?
I have returned to this forum from Astronomy with this question because it immediately got down-voted. Maybe these hypothetical questions are more appropriate here? I am happy to take advice from Worldbuilding forum veterans.
I am in the process of building a hypothetical solar system very similar to ours with only a few changes. I would like to test the viability of my modifications mathematically. Procedural answers are most welcome. 710
As I have been advised in the comments by <PERSON> and <PERSON>, I am adding additional information for clarity below:
My objective for moving planets is two-fold: (1) that I can create calendars and astrology specific to my "Earth," and (2) that Venus and Mars will orbit on the furthest edges of the habitable zone and therefore be able to have liquid water in some quantity somewhere on their surfaces.
My concern is that by moving my hypothetical Venus, Earth, and Mars so close together they will affect each other so significantly during conjunctions that my solar system build is no longer viable, i.e., the hypothetical planetary orbits will not be stable over billions of years as ours have been.
As advised by <PERSON>, I have edited the title question to specify the hypothetical semi-major axes.
As advised by planetmaker from Astronomy, I am adding this additional information: planetmaker asked "How big a disturbance (in planetary orbit) is too big?" and "What time scales are we talking about?" An orbital disturbance is too big if the hypothetical Venus, Earth, and Mars cannot plausibly have retained their proposed semi-major axes long enough for habitable worlds to evolve. "Habitable" should be taken to mean a world with a liquid water ocean, temperate climate, and breathable air in at least some regions, which indicates the evolution of complex, oxygen-producing lifeforms. (I am aware that Mars' size is considered responsible in part for the loss of its oceans. I may increase the size of my Martian planet if necessary, but right now it is not relevant.) This leads me to suggest that a timescale of 4.5 billion years should be considered as baseline.
Thank you for your help! 710