I recently read and enjoyed Cody J. Shakespeare and Jason H. Steffen’s effervescent “Day and Night: Habitability of Tidally Locked Planets with Sporadic Rotation.” They explain that potentially habitable planets orbiting red dwarf stars would need to be close enough to their suns that tide locking—explanation here—would be inevitable. Red dwarfs being the most common type of stars, it follows that tide-locked worlds could be the most common variety of potentially habitable worlds. The traditional view is that libration aside, a tide-locked world’s orientation with respect to its sun would be very stable over long periods. Thus the old notion that all the volatiles would inevitably solidify and precipitate onto the forever night side (not actually the case, as even a thin atmosphere can transfer heat surprisingly well).
Shakespeare and Steffen’s model suggests that under certain conditions, tide-locked worlds can “flip,” reorienting themselves so that what was once in night is now in day, and what was formerly illuminated is now in shadow. This would be accompanied by extraordinary climate change. Even more impressively, it would occur over what are short time scales, even by human standards.
While this is terrible news for anyone living on a world orbiting a red dwarf—particularly if they don’t want to adapt their agriculture from Saharan heat to Antarctic cold overnight—this sort of process is a godsend for SF authors. All one needs to do is plant a human community on such a world (perhaps because the humans no longer believe in due diligence, because they were defrauded, or because they had no choice), orchestrate a flip and watch plot ensue. It practically writes itself. Or it will, once news of the paper percolates through the SF community.
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