Still in the mood of Darkover under the red sun, here's this planet which may be suitable for life as we know it. The planet has an atmosphere and weather, which is promising. In the books Darkover is said to orbit a red giant, which is variable and fading in intensity. But there are also planets that orbit red dwarfs, which are small stars which are not as bright as our Sun but could provide enough light and warmth for life on a planet nearby. If Darkover's star is a red giant, which is an overblown late development of a previously Sun-like star, then that red giant would have consumed all its inner planets as it slowly expanded. That would make Darkover probably an outer planet which was warmed up by the red giant, enough so that life could evolve. However the time frames for evolution of life and the development of a red giant stage may not be compatible. If Darkover orbited a red dwarf though, its "month" of about 40 days (mentioned in the Bradley books) may actually be its orbital period, or its "year." Seasonal differences taking longer than 40 days might be caused by other factors such as interstellar gas which dims the star's light, or variations in the star itself.
Marion Zimmer Bradley was a storyteller, not an astronomer, so she never did any astronomical fact-sheets for the Darkover system. That has not stopped fans like me from speculating on just how the World of the Red Sun came to be.
The title of this piece, "A World Lit Only by Fire," comes from a book by historian William Manchester which I have not read, but I loved the title.
Acrylic on illustration board, 10" x 7", January 1998.