A pair of similar celestial bodies coming near each other

In my conworld I have two moons (they could be planets if desired as long as they can stay 'close' to a larger nearby body) of habitable size. I want to reality-check and provide an explanation for why they would have certain properties.

For my purposes I would like these two bodies to have a couple interesting properties:

1. Large Equatorial Ridge or Oblong shape.

While I want the body to be large enough to be habitable, I would like it to have, in essence, two sides - like a coin.

Obviously a coin-shaped planetary body would be far too extreme, but something like Iapetus with a moderately more pronounced equatorial ridge would effectively divide the body into two regions.

Bonus if there is some reason why it is extremely difficult for an intelligent to cross to the other side, even with approximately contemporary technology or if there is some reason why they would not do so.

2. Rare 'approach event' making inter-body transit significantly cheaper

The way I picture this, at some point the bodies get much closer to each other than usual. This should be visible to the naked eye and a major event, but should be somewhat uncommon (period of at least a 'year'). During this event travel between the two bodies should be much easier than outside of the event (e.g. no need to maintain orbital velocity, just get close enough for the other body's gravity to capture you).

I want to know how long this 'approach event' could last, and what the distance and relative speed could be. Obviously if they get too close then their gravities will rip them apart and they will cease to be habitable. Obviously if their relative speed is too slow then they will get too close and either collide or have gravity rip them apart - again ruining habitability.

Just how close, how slow, and for how long can such an approach be made. How cheap can inter-body travel be during this period? Could there be time and proximity enough for a space-elevator-like situation?

I'd like to know how such a celestial configuration could be possible and what unforseen consequences it could have.

posted over 5 years ago

LambdaBeta‭

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