As stated a tidally locked world that has complete 1:1 begins to spin slowly. It starts slowly, a 2:1 ratio that steadily ramps up over the course of a month to one rotation every month, which would eventually continue increasing exponentially until it reaches an Earth-equivalent resonance (365 days in a year, approximately.) What sort of natural disasters occur on this world not related to the sudden loss of sunlight/appearance of it in either half of the globe?

Some other information: The night-half of the planet is covered in a singular, hemisphere-wide icecap comprised of 70% of the planets water at -60 celsius from 90* S to approximately 10* N (correct me if an earth-like planet would be warmer at that latitude). There is a band of highly volcanic land on the terminator caused by tidal stresses. For comparison points, there are currently 400-500 mph windstorms resulting from the thermals on this planet, it would be nice to see if disasters would be better or worse than those. Portions of the terrestrial planet have abnormally thin crust comparable to oceanic plates. There are reasons for this not related to the question.

Edit: Given the information in the replies, here is more helpful information: suppose the speed up was slowed to a gradual increase in speed per year, about an hour every year so that in 500-600 years the planet would have one or two week long day cycles after the initial one month start-up. How would the cataclysm differ from the above with this information?

There is also constant cloud cover on the nightside sustained by atmospheric condensation. Can this prevent heat radiating into space from that side?

Lastly most natural life on the planet evolved fro m extremophiles to A) avoid regular disasters through regular mass migration and B) survive temperature extremes, as well as to possess the bare minimum of genetic complexity for an average-sized lifeform for another reason not important to the discussion.

Otherwise I am quite satisfied with the information I have received, I just need to find a process to sustainably slow the planetary "jumpstart."

  • $\begingroup$ Follow-up question, would the rate, severity, and nature of these disasters change if the rate of the wind-up was slower? $\endgroup$
    – Quinn
    Aug 17, 2023 at 0:44
  • $\begingroup$ Quite a contradicting set of existing disasters. Volcanic land at terminator? If a planet is tidally locked to its nearest neighbor, it does no longer experience crust stress, so no volcanism due to stress. Also terminator is something irrelevant to tidal or volcanism, it's a mere boundary between lit and unlit sides. There would be high winds at terminator, but not volcanoes. Windstorms? What causes the winds to travel back to lit side? Normally you get balanced pressure for the unlit side, but temperature there should be below freezing for air, thus atmosphere would all solidify over time $\endgroup$
    – Vesper
    Aug 17, 2023 at 4:35
  • $\begingroup$ Also, how long already does a world remain tidally locked? Does it have librations like the Moon? Librations could allow the atmosphere to still remain on the lit side, as frozen parts of it would melt under sunlight. And finally, who is spinning up that world? It's one HELL of energy investment, other topics here listed billions of years for the most fantastic projects to spin up Venus, and you suddenly say "exponentially". Magic? $\endgroup$
    – Vesper
    Aug 17, 2023 at 4:40
  • $\begingroup$ @Vesper The terminator also functions as the "equator" between which parts of the planet are facing the sun and which aren't; I read somewhere that those sections receive stress due to the gravity of the sun. There are studies on the way the sun affects plates, and the temperature difference makes the crusts differ in thickness causing an equatorial ring of fire (the real life ring is caused by the continents acting on the thin pacific plate). I didn't mention that the winds travel to the lit side, though two cool and dry currents carry less dramatic airflow to the perihelion. $\endgroup$
    – Quinn
    Aug 17, 2023 at 6:41
  • $\begingroup$ @Vesper I didn't mention anything about the planets sustainability, so frozen air is irrelevant. It has minor liberations that I don't have the means to quantify right now but they are mostly unnoticeable without a landmark. The means by which the planet begins spinning are IRRELEVANT to the topic, too. $\endgroup$
    – Quinn
    Aug 17, 2023 at 6:45

2 Answers 2


Tidal locking occurs when an object's rotation period matches its orbital period around another object, causing one side to always face the other. In the context of a planet, this typically means that one hemisphere of the planet always faces its star (or other primary body) while the other hemisphere remains in perpetual darkness. If this tidally locked world were to start spinning, it would experience significant changes that could lead to various natural disasters. Here are some potential scenarios:

Seismic Activity: The sudden change in the planet's rotation could lead to increased seismic activity as the crust adjusts to the new distribution of forces. This might result in earthquakes, tsunamis, and volcanic eruptions.

Weather Pattern Changes: The shift from a tidally locked state to a spinning planet would dramatically alter the global weather patterns. The side that was previously always facing the star would experience new temperature differentials due to day-night cycles, which could lead to intense storms, hurricanes, and other extreme weather events as the atmosphere adjusts to the changing dynamics.

Ocean Current Disruption: The oceans' currents are influenced by the planet's rotation and temperature differences. The sudden change in rotation would disrupt established ocean currents, potentially leading to changes in sea levels, altered marine ecosystems, and more intense currents that could cause coastal flooding and erosion.

Magnetic Field Instabilities: The planet's magnetic field, which is generated by the movement of molten iron in its core, could become unstable during the transition from tidally locked to spinning. This could lead to fluctuations in the magnetic field, affecting navigation systems, communication networks, and potentially exposing the planet's surface to higher levels of solar and cosmic radiation.

Geomagnetic Storms: Instabilities in the planet's magnetic field could lead to geomagnetic storms, which are bursts of energy from the sun that interact with the magnetic field and atmosphere. These storms could disrupt power grids, satellite communications, and other electronic systems.

Ecological Changes: The abrupt shift in the planet's rotation could lead to massive disruptions in ecosystems. Plants and animals that adapted to the previous tidally locked environment might struggle to adapt to the new conditions, potentially causing species extinction, shifts in biodiversity, and ecosystem imbalances.

Auroras: As the magnetic field fluctuates during the rotation change, it could lead to auroras appearing in different areas of the planet than before. These auroras could become visible at different latitudes and longitudes, creating stunning light displays in the sky.

It's important to note that the extent and nature of these natural disasters would depend on various factors, including the planet's size, composition, atmosphere, and the speed at which it starts spinning. The process would likely be complex and unfold over a significant period of time, potentially causing a series of cascading effects.

  • $\begingroup$ Would they be less dramatic if the rate of speed was slowed down? Suppose that over two centuries the days became more normal, perhaps two to three real life days to one of this planets' days by then. $\endgroup$
    – Quinn
    Aug 17, 2023 at 6:49
  • $\begingroup$ You don't seem to account for initial climate on a planet tidally locked to a star. The night side, if allowed to not get lit for enough time, would absorb the entire atmosphere in form of ice, water or oxygen, no matter. Helium should remain gaseous, if the planet is large enough and far enough to be able to retain it in its atmosphere. So, no ocean, no currents, no winds, no ecosystems, no civ disruptions. Magnetism-related effects, tectonic-related, planet shape-related effects all would happen, but not this rather simple set of effects. $\endgroup$
    – Vesper
    Aug 17, 2023 at 7:20
  • $\begingroup$ Not sure the shift in weather patterns would be that 'devastating'. Assuming the planet has a thick enough atmosphere to support liquid water the thermal disequilibrium between the day and night sides would already be causing cyclonic level wind speeds & there wouldn't/shouldn't be many large bodies of open water because they will only exist in the terminator band (unless of course all/most of that region is covered by water). In fact given enough time I would expect weather patterns gradually moderate depending on it's final rotation speed. The earthquakes & floods though? Woo who!!! $\endgroup$
    – Mon
    Aug 17, 2023 at 7:37
  • $\begingroup$ @Mon would the atmosphere not get locked up on the night side as ice, regardless of its thickness? $\endgroup$
    – Vesper
    Aug 17, 2023 at 7:52
  • $\begingroup$ Point (1): There should still be a degree of circulation via the terminator zone. Assuming the planet is 'Earth like' in more or less all ways but the fact it's tidally locked super hot air and water vapor from the 'hot' side of the planet will circulate to the 'cold' side and cool. Some of it will freeze but not all before it recirculates back to the hot side. $\endgroup$
    – Mon
    Aug 17, 2023 at 11:09

EDIT: Since there are really planets that both are tidally locked and have an atmosphere, I assume that your description of planet's climate is plausible. Therefore, assuming that the planet does have harsh winds, liquid water at terminator, death valley at the center of day side and an antartic-like permanent night on the opposite.

Now, as the planet starts to spin up, changes should happen. And there are quite a lot of them, all planet-wide.

  • First, flooding. After the planet has revolved to face the icecap to the sun, it would start to rapidly melt, produce clouds with increased water vapor, melted water would rush out to form planet-wide oceans, flooding the lower parts of the planet and cooling the overheated rock that was under the sun, forming a thick layer of clouds and causing massive rainfall. The winds would have reversed by then, leading to hurricanes of 6-7 level of strength compared to "usual" 5-level winds. This cloud formation might induce enough increase of planet's albedo to both lower its average temperature and decreasing available sunlight, or potentially cause a greenhouse effect to allow accumulating heat below the cloud layer. This climate change alone is extreme enough to overhaul the inhabited surface, probably wiping the above-ground life off the planet. But, it's not the end of story;
  • Second, tectonic activity. Spinning up a planet, no matter how fast, involves it to change shape of equipotential surface for gravity field, which corresponds to general shape of the celestial body that's confined by its own gravity. For example, Earth's distance from pole to pole is about 42 km shorter than between most distant points at its equator (not counting mountains). So, the parts that would become poles due to spin-up would have to drop about 11 kilometers (more if your planet is larger than Earth, less if smaller), while the equator should bulge for about the same. Also if the spin is not magically applied to the entire thickness of the planet, there will be frictions at the Mohorovicic discontinuity on your planet, causing more rehaul of the surface, as well as heating and spinning up the core and mantle, which would also likely cause them to develop planet-wide magnetic field. "Earthquake" is not the word to describe what should happen, it'll be more like "volcanoes everywhere!!!11". Such conditions should last for a good thousand years, gradually subsiding as the spin-up would stop, but only a VERY slow spin-up could reduce the magnitude of this.
  • Third, after filling the planet's surface with enough water to reach everywhere, and enough lava to release more gasses from under the crust into the atmosphere, the very dark, electrified and hot era would start over the entire surface of the planet, depending on what would be the angle between the new axis and the planet's orbital plane, the larger the harder, as bigger yearly fluctuations of insolation would cause more climate perturbations, and all that on top of emerging crust overhaul. Acid rains would be omnipresent, the ocean consistence would have unpredictably changed, most likely life would get reduced to anaerobic bacteria that could live along volcanic activity and feed on H2S, for example, and that would last until the new shape of the entire planet would form and stabilize at least to a grade of emergence of stable tectonic plates either below or above the new water level;
  • Fourth, increasing speed would start causing tides from the star, the faster you spin, the higher the tide would be, but compared to planetary matter rehaul due to tectonics these are negligible, here on Earth solar-induced tides are about 2-3 centimeters high. Yet I think I should mention them.

Every other thing that's called a disaster here on Earth is not relevant to the planet that has just been wiped of life.

Speaking about whether slower spin-up could cause less trouble - well, maybe if the entire spin-up would take millions of years, the tectonic overhaul level would be less dramatic to allow life to accommodate to chaging atmosphere and ground conditions, or at least to retain the majority of crust stable. Your description looks like the spin-up is lasting several years at most, that would cause too much turmoil for any highly organized life to have a chance at survival.

  • 1
    $\begingroup$ There IS an addional source of heat on the dark side: convection. If thats enough to stop freezing everything depends on the thickness of the atmosphere, the speed of winds and the hotness of the day side. If that allows for liveable conditions? Dont know. Maybe handwave it that the dark side is like antarctica and the light side like arrakis, with a narrow band with moderate temperatures (but severe storms) at the terminator. Edit: Remember there are parts of our planet that are in darkness for months. It does not get nearly cold enough there for the atmosphere to freeze. $\endgroup$
    – LazyLizard
    Aug 17, 2023 at 8:38
  • $\begingroup$ @LazyLizard well nice comment, yet months are nowhere near enough to freeze the atmosphere, as the energy loss via radiation, which is the only way to cool down something in space, is very small for such low temperatures as 200K, the lower the worse, it would take thousands of years to lower the ambient temperature on the most covered spot on a tidally locked planet to make it rain oxygen there. But tidal locking, especially vs the sun, is a process that lasts millions of years, so there would be enough time to freeze the atmosphere. $\endgroup$
    – Vesper
    Aug 17, 2023 at 8:48
  • $\begingroup$ But, you have a valid point in that the thick atmosphere could work as a heat transfer mechanism to the night side with enough power to avoid the disaster, it however depends on starting conditions, but since the cooling process has a runaway part, if it would start then the planet would lose the atmosphere. But if not... I think the tectonic part still would stand, as well as flooding part. $\endgroup$
    – Vesper
    Aug 17, 2023 at 8:52
  • $\begingroup$ Ran a quick google search for atmosphere dynamics on tidally locked planets, found out that there are planets that are tidally locked and have a metastable atmosphere with likely enough heat transfer to their night side to prevent freezing up. So, a set of planet's parameters should exist that would allow climate and life on the terminator and its vicinity. Hmm. $\endgroup$
    – Vesper
    Aug 17, 2023 at 8:59
  • $\begingroup$ @Vesper I should mention that there are very thick, almost constant cloud cover on the night side due to the condensation of the atmosphere there. Is that enough to simulate a green house effect in that area? $\endgroup$
    – Quinn
    Aug 19, 2023 at 0:00

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