So, I've got a fantasy world where there is a super-earth with Earth-like gravity (aim is approximately half-again the diameter of Earth) that is the homeworld of non-native humans(introduced to the world way back when) and orbiting it is a habitable moon with Earth-like gravity as well that is inhabited by non-native elves.

The premise that I had had in mind for this was that the super-earth would be composed of mostly lighter elements (barring the core and the like) while the moon is comprised of heavier elements. the idea being that the two would balance out. The moon is smaller but heavier while the super-earth being bigger but lighter.

Now, what immediately comes to mind as an issue is the moon; that thing is going to wreak havoc tidally and tectonically and I have highly tectonically and volcanically active regions, as well as some pretty damn high tides, being an issue for any form of coastal life beyond that which is adapted to it.

Things like the geology and topography are not set as of yet, beyond one loch-like-area in which the story is based, but I'm hoping it could be roughly parallel to that of earth.

A lot of what could be said about the planet is still in flux, but I am aiming for something fairly similar to that of the earth (no idea about the moon) and beyond the basics mentioned above I can work with what needs to be done to make it practical.

I did have an idea as to the moons closest point always being along the equator and that being where most of the tectonic activity happens with a byproduct being that a sand dune type desert had formed along the equator due to a variety of factors.

Anyway... thoughts? Mind this is a fantasy setting, but one that isn't too far out there and which is heading toward its enlightenment age. Due to the elves fleeing the moon because of a cataclysm much of the super-earth is known, it has been mapped by them through a telescope and far-seeing items. Furthermore, the diameter has been calculated properly with a metric style unit of measurement having been determined.

Much of the world is known, at least in the broad strokes. I'm just trying to hammer out the details.