All these planets are necessarily tidally-locked to their star.
That represents an extremely poor environment to try to evolve life in. The only temperate place would be a ring at the terminator with the sun permanently just above the horizon.
With a very massive moon -- or a double planet, like Pluto/Charon, it might be possible to avoid tidal lock.
One of he planets receives 0.67, and the other, 0.257 of the Sun's light flux. The sun-facing surface, with the star directly above, may be the most habitable part, while the other side is likely colder than Antarctica.
With an ocean of liquid water evaporating on the sunlit side and condensing away from it, but flowing back through the ocean (and even rivers), the sunlit area may (theoretically) have relatively a temperate climate, as opposed to being a star-scorched dry desert.
This system is less than 5 parsecs / 16 LY from Sun, which likely makes it one of the systems more amenable to detailed research, as bigger telescopes become available.
More probably up to an equilibrium. Everything getting to the cold side will freeze and stay there but it must get there first.
My naive model: atmosphere on the warm side goes up, moves with hot humid air toward the cold side, goes down and back to the warm one with cold dry air.
Less naive model: we have three large convection cells here on Earth between the pole and the equator. Maybe they have several cells there too. That could slow down the transfer.
Furthermore dry is never 100% dry and when there is little water left the transfer will slow down. How much water will be left and for how long, I can't say. There could be the equilibrium I'm thinking about or not.
Other variables: volcanoes melt stuff locally, glaciers flow to lower ground, continents move.
The migration of water to the dark side changes the center of mass for the planet, right? Might that be enough, especially if there are any other bodies around to throw in some chaos, to pull the ice back into the warmer region?
Right, but not that's the same thing I'm wondering about. I'm wondering if the change in mass distribution due to ice migration might set things out of balance such that movement is possible. Further, that could still happen with effective tidal lock. Perhaps it's a "punctuated equilibrium" kind of thing where it's stable for a relatively long period until enough ice builds on the dark side that the planet "rolls" and stays in that position until enough ice melts and migrates again.
Life on such a world wouldn’t be so bad. It’s basically an inverted ring world. Belief systems would arise to discourage inhabitants from going too far off the ring, either into the burning desert eternally punished by the sun or the icy tundra shrouded in eternal darkness.
An advanced version of this civilization might think of the Earth as uninhabitable: how would you power anything without a builtin planet-scale, locally operable gradient?
At first armies can march in one direction of the ring or the other, with every natural defense point being sort of a Thermopilae situation
Then, technology progresses and certain machines may allow smaller groups to traverse outward for limited periods of time. Analogous to our submarines?
Would then flight make the world "flat" and globalized?
They can't lay cables across the scorching dor icy deserts, so worldwide comm must either follow the ring or be satellite-based
That represents an extremely poor environment to try to evolve life in. The only temperate place would be a ring at the terminator with the sun permanently just above the horizon.
With a very massive moon -- or a double planet, like Pluto/Charon, it might be possible to avoid tidal lock.