[Space] Gliese 581

[Critical]

Originally Posted by Fred Brackin

To the best of my understanding the habitable zone of any M-class dwarf is going to be filled with tidally locked worlds. You'd need some sort of exotic scenario such as a double planet system tidally locked to each other but still spinning relative to the star or something like that.

I’m not sure why you would need precisely that scenario or why any such scenario would be “exotic.” Consider the simple case of a large planet with several moons that may or may not be tidally locked to the planet. In our own solar system, several of Jupiter and Saturn’s moons are not tidally locked, several others orbit fast enough for a long day/long night scenario to happen, and we essentially have a double planet in the form of Pluto and Charon.

Another interesting point about red dwarfs is that their UV output is minuscule and could allow planets in remote orbits to retain far more geothermal energy by way of not having their upper atmospheres thinned out by incident UV light. You could have an Earth-sized planet well beyond the Goldilocks zone that retains enough of its own geothermal heat that it can maintain liquid water on the surface for billions of years. In theory, even a rogue planet could exist like this, especially with one or more moons to engage in tidal heating processes.

There are so many red dwarfs compared to other stars, perhaps as much as 75% of the stars in the galaxy, that you are going to find all sorts of “exotic” scenarios if you examine enough of them.