How close could another solar system be without adversely affecting our own?

I would like to know how close two planetary systems could be without having an adverse effect on each other. My goal is to drastically improve the chances of having habitable planets near enough that humans having the technology of today could realistically send manned spacecraft to other planetary systems and even have useful communication and trade.

I'm thinking specifically about our own solar system, and to reduce the guessing, let's assume the other system is identical to ours: same sun, same planets. Their "Earth" could be lifeless, I don't think it affects anything.

More difficult to define is what it means to "adversely affect" our own system. I have a few ideas, but these are not 100% set in stone:

• The other sun should not be brighter in our sky than Venus at its brightest.
• It should not be possible to detect any gravitational effects on our outer planets due to the presence of the other system using the best instruments to date.¹ - No stealing of planets.
• There should be no weird electromagnetic effects like auroras from the other sun other than the visible light and whatever else is expected from observing another star.
• I do not care about the Oort cloud, simply because I hope that the distance will be less than 1 ly.
• I also don't care about any effect on human mythology. Early astronomers would likely find that this star is special and much brighter than the others, which is fine.

A bonus question: Would it change if we imagine a number of these systems packed in a sphere-packing formation? If I understand correctly, it would amount to 12 neighbors equidistant from the Sun.

^{1. I admit having no clue how much we can detect, so this is one requirement that may have to go.}

posted over 5 years ago

pipe‭

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