Perpetual

Some planets thought to be locked in place around their parent star may actually be able to rotate, creating climates that are stable for long enough for potential life to arise – as long as any inhabitants don’t mind sudden disruption.

Many exoplanets(planets orbiting stars that are not our sun) that closely orbit white dwarf stars are believed to be tidally locked by their star’s gravity, so these worlds have perpetual day and night sides that are extremely hot or cold. It has been thought that life could evolve on such a planet, perhaps living near the boundary between the two sides.

Now, Jason Steffen and Cody Shakespeare at the University of Nevada, Las Vegas, have found that some of these worlds may be able to unlock and rotate before locking up again with day and night flipped, according to simulations of millions of orbits in such systems.
–New Scientist