Would a tidally locked planet have tectonic plates and continental drift

[alans]

If a planet was tidally locked, so only one side of the planet faced the star (think Trappist system) would the tidally locked planet be less likely to have tectonic plates and continental drift?


My motivation is just trying to imagine factors that could affect the evolution of planets around white dwarfs where the planets are close to the star.

[Van Rijn]

If a planet was tidally locked, so only one side of the planet faced the star (think Trappist system) would the tidally locked planet be less likely to have tectonic plates and continental drift?

I’m not a geologist, but I believe it would depend on other factors. Mars is thought to be too small to retain sufficient internal heat for much of that to happen and developed a thick crust. So small worlds are probably out. Venus is large enough, but lost its water, and the rock is much stiffer without it. Also, the high surface temperature can affect geological processes as well. But something like a tidelocked Earth or superearth, retaining water might well manage it.

My motivation is just trying to imagine factors that could affect the evolution of planets around white dwarfs where the planets are close to the star.

That’s an interesting situation because if the orbit isn’t almost perfectly circular, there will be a lot of tidal heating. From what I’ve read about possible habitability, a big issue is how such a planet would retain water and atmosphere until the white dwarf got down to a decent surface temperature. On the positive side, even a fairly small world would remain geologically active - though it could easily be too active.

[dtilque]

My motivation is just trying to imagine factors that could affect the evolution of planets around white dwarfs where the planets are close to the star.

Have you considered the history that such planets must have? Stars don't start off as white dwarfs, of course. White dwarfs are the end point of stellar evolution and they've all gone through the red giant phase. Which means that any planets that started off close to the star are probably gone. I'm not sure that all planets engulfed in red giant's atmosphere are necessarily gone, but any that survive will be a ghost of their previous selves. Only the most refractory minerals will remain.

Also because of drag from the stellar atmosphere, the planet must have started off relatively far from the star to begin with, although it would likely end up very close to the star by the time the atmosphere is blown off.

[kzb]

First of all Trappist-1 is a red dwarf not a white dwarf. As dtilque said it's probably a bit academic with a planet close to a white dwarf, it will likely be substantially wrecked to start with.

I don't see why there wouldn't be substantial geological activity, assuming we are talking about a rocky, Earth-sized planet. The tidal heating will be substantial unless the orbit eccentricity is very low. Back in the past, heating would've been very high because the very fact it is tidally locked and in a circular-ish orbit means a lot of energy got converted to heat in the planet. More so than Earth in fact, even though these close-in planets won't have permanent moons.

If it is a rocky planet it will likely have a similar inventory of heat producing radionuclides to Earth.

There are a couple of "howevers", there always are.

1) If the system is very old, radionuclides will have died out and the heat stored in the planet will have escaped. Geological activity will grind to a halt. This will happen to Earth one day.

2) Rocky superearths are thought to have very thick crusts which prevent plate tectonics. If the theories are correct of course.

[Roger E. Moore]

I believe small terrestrial planets would have thin crusts (like Mars) that would harden in place once the mantle cooled down. I think only Venus and Earth have actual tectonic plates.

ERROR: Only Earth does, not Venus.

[Roger E. Moore]

This suggests a tidally locked planet can have continents.

The influence of a sub-stellar continent on the climate of a tidally-locked exoplanet

Neil T. Lewis, F. Hugo Lambert, Ian A. Boutle, Nathan J. Mayne, James Manners, David M. Acreman

Previous studies have demonstrated that continental carbon-silicate weathering is important to the continued habitability of a terrestrial planet. Despite this, few studies have considered the influence of land on the climate of a tidally-locked planet. In this work we use the Met Office Unified Model, coupled to a land surface model, to investigate the climate effects of a continent located at the sub-stellar point. We choose to use the orbital and planetary parameters of Proxima Centauri B as a template, to allow comparison with the work of others. A region of the surface where Ts>273.15K is always retained, and previous conclusions on the habitability of Proxima Centauri B remain intact. We find that sub-stellar land causes global cooling, and increases day-night temperature contrasts by limiting heat redistribution. Furthermore, we find that sub-stellar land is able to introduce a regime change in the atmospheric circulation. Specifically, when a continent offset to the east of the sub-stellar point is introduced, we observe the formation of two mid-latitude counterrotating jets, and a substantially weakened equatorial superrotating jet.

https://arxiv.org/abs/1802.00378

[Roger E. Moore]

Did Ancient Mars Have Continents? (from 2015) With the help of a rock-zapping laser, NASA's Mars rover Curiosity has detected Red Planet rocks similar to Earth's oldest continental crust, researchers say. This discovery suggests that ancient Mars may have been more similar to ancient Earth than previously thought, scientists added. Earth is currently the only known planet whose surface is divided into continents and oceans. The continents are composed of a thick, buoyant crust rich in silica, whereas the seafloor is made up of comparatively thin, dense crust rich in silica-poor basaltic rock. Previously, scientists had suggested that the continental crust may be unique to Earth. The silica-rich rock, the idea goes, resulted from complex activity in the planet's interior potentially related to the onset of plate tectonics — when the plates of rock making up Earth's exterior began drifting over the planet's mantle layer. "Mars is supposed to be a basalt-covered world," study lead author Violaine Sautter, a planetary scientist at France's Museum of Natural History in Paris, told Space.com. The findings are "quite a surprise," she added. Sautter noted that recent orbiter and rover missions had spotted isolated occurrences of silica-rich rock. The researchers suggest these silica-rich rocks might be widespread remnants of an ancient crust on Mars that was analogous to Earth's early continental crust and is now mostly buried under basalt.

https://www.space.com/29967-ancient-...ity-rover.html

[Roger E. Moore]

https://en.wikipedia.org/wiki/Plate_...ics#Exoplanets

On Earth-sized planets, plate tectonics is more likely if there are oceans of water. However, in 2007, two independent teams of researchers came to opposing conclusions about the likelihood of plate tectonics on larger super-Earths, with one team saying that plate tectonics would be episodic or stagnant, and the other team saying that plate tectonics is very likely on super-earths even if the planet is dry.

===

Inevitability of Plate Tectonics on Super-Earths

Diana Valencia, Richard J. O'Connell, Dimitar D. Sasselov

The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.

https://arxiv.org/abs/0710.0699

[Roger E. Moore]

Another arXiv paper suggesting that a tidally locked exoplanet can have continents.

Surface Imaging of Proxima b and Other Exoplanets: Topography, Biosignatures, and Artificial Mega-Structures

Svetlana V. Berdyugina, Jeff R. Kuhn

Seeing oceans, continents, quasi-static weather, and other surface features on exoplanets may allow us to detect and characterize life outside the solar system. The Proxima b planet resides within the stellar habitable zone allowing for liquid water on its surface, and it may be Earth-like. However, even the largest planned telescopes will not be able to resolve its surface features directly. Here, we demonstrate an inversion technique to image indirectly exoplanet surfaces using observed unresolved reflected light variations over the course of the exoplanets orbital and axial rotation: ExoPlanet Surface Imaging (EPSI). We show that the reflected light curve contains enough information to detect both longitudinal and latitudinal structures and to map exoplanet surface features. We demonstrate this using examples of Solar system planets and moons as well as simulated planets with Earth-like life and artificial megastructures. We also describe how it is possible to infer the planet and orbit geometry from light curves. In particular, we show how albedo maps of Proxima b can be successfully reconstructed for tidally locked, resonance, and unlocked axial and orbital rotation. Such albedo maps obtained in different wavelength passbands can provide "photographic" views of distant exoplanets. We estimate the signal-to-noise ratio necessary for successful inversions and analyse telescope and detector requirements necessary for the first surface images of Proxima b and other nearby exoplanets.

https://arxiv.org/abs/1711.00185

[kzb]

https://en.wikipedia.org/wiki/Plate_...ics#Exoplanets

On Earth-sized planets, plate tectonics is more likely if there are oceans of water. However, in 2007, two independent teams of researchers came to opposing conclusions about the likelihood of plate tectonics on larger super-Earths, with one team saying that plate tectonics would be episodic or stagnant, and the other team saying that plate tectonics is very likely on super-earths even if the planet is dry.

===

Inevitability of Plate Tectonics on Super-Earths

Diana Valencia, Richard J. O'Connell, Dimitar D. Sasselov

The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.

https://arxiv.org/abs/0710.0699

I think you're right Roger, I don't think there is any certainty about plate tectonics on superearths. See this for example:

GEODYNAMICS AND RATE OF VOLCANISM ON MASSIVE EARTH-LIKE PLANETS

Hotter—that is, bigger or younger—planets must recycle plate faster, so a plate has less time to cool. In addition, higher potential temperatures produce a thicker crust. Both factors tend to produce positively buoyant plate, which is harder to subduct. This effect is more severe for massive planets because of their greater gravity.

https://iopscience.iop.org/article/1...#apj292293s4-5

[eburacum45]

This is a useful summary of the various possibilities with tidal-locked planets.
https://worldbuildingpasta.blogspot....-part-ivd.html

The formation of continents is discussed here;
https://worldbuildingpasta.blogspot....ntinentaldrift

Supercontinents might form, and may be drawn towards the subsolar point by tidal effects, but this condition may not be permanent. The disposition of continental crust on such a planet would affect the climate significantly.