Does a tidally locked planet have seasons?

Question

Could a tidally locked planet have seasons?

According to my understanding, a tidally locked planet rotates around itself exactly once per rotation around its sun. However, if the axis of rotation of the planet is significantly off from the axis of rotation around the sun, wouldn't it still have seasons?

Or does tidal locking require that the axis of rotation of the planet about itself be perfectly orthogonal to the axis of rotation of the planet about its sun?

If not, what would happen to a "tidally locked" planet with an axis of rotation "pointing towards" its sun (sort of like Uranus)?

Answer 1

I'm not a expert in this area, but I think the mechanism of tidal locking works better when the rotation axis is aligned or nearly aligned with the orbital axis than it does under other circumstances.

But if you had a planet for which the day equaled the year but for which the rotation inclination was non-trivial it would experience seasons from it's inclination.

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In addition, any tidally locked planet with non-trivial orbital eccentricity would have seasons owing to differing distances from the primary.

Such seasons would differ a bit from the ones that we are used to because

1. they would come uniformly to the whole globe instead of the northern and southern hemispheres being out of phase
2. the winter would be longer than the summer on account of Kepler's laws

(Non-tidally locked planets with eccentric orbits also experience this effect. Earth's current orbital eccentricity is about 0.017 meaning that there is about a 6.8% variation in the energy received from the sun over the course of the year.)

Answer 2

A presentation on the SETI Weekly Seminar series (available on Youtube) points out that tidal locking (e.g. expected of a planet in the habitable zone of a red dwarf) can involve higher muliples than same-face-shows, and in fact an eccentric orbit favors an odd half multiple (3:2 like Mercury).

There is also orbital inclination to consider. The pattern of insolation changes due to precession and whatever you call the sliding of the point where the orbit crosses the ecliptic, but I don't know if that cycle is fast enough to call a season. (What do you call Titan's 10000 year cycle of north/south climate alternation?)