# Tag Info

53

If your tidally-locked planet captured a large moon, sort of like the one we have here on Earth, the tidal forces of the moon could be stronger than the tidal forces from the star. This would result in the planet gradually losing its tidal lock to the star in exchange for a tidal lock with the moon.

52

A planet in our very solar system has actually gone through such a shift! Venus currently has a 243-day long retrograde spin, but likely didn't always. The current theory says it started with the usual fast spin and underwent tidal locking normally. And it would have stopped there, but Venus's thick atmosphere generates thermally driven atmospheric tides ...

39

Rocking Your continent is floating. Maybe it is rocking back and forth as it floats. That can happen with floating things. Any number of forces can put a body into an oscillating motion. As your continent rocks back and forth the water contained in it will flow back and forth, moving toward the low side. I could imagine the rocking being subtle ...

22

Yes! In fact, we can find it right in our solar system. Mercury is the closest thing to what you would want. It is in a 3:2 spin-orbit resonance, meaning 3 Mercurian days happen every two Mercurian years. Since it has no atmosphere, there is very little heat distribution going on at the surface, so the day side is scorching and the night side is freezing. ...

21

Maybe you can get some inspiration from the Uru People that live over Lake Titicaca. They create artificial floating islands, with small houses on it, with a plant called Totora. This plant commonly grows at a water depth of 2.5–3 m (8.2–9.8 ft) but occurs less frequently as deep as 5.5 m (18 ft). https://en.wikipedia.org/wiki/Uru_people https://en....

21

In order for the fragments not to simply reform into a single body from their own gravity, the damaged moon would have to meet certain criteria. Either it would have to be within the planet's Roche limit, or the fragments would have to have been launched at above the moon's escape velocity. Since you want a slowly evolving situation, the latter can be ...

13

Unfortunately the answer is no. Serious props to you if you want to have a go at coding this. There is probably a PhD in it. One of the primary resources on the topic is the Admiralty Manual of Tides (NP 120). It has been a few years since I worked in the discipline and theory may have progressed but tidal prediction is primarily done by analysing harmonic ...

13

Perhaps on your world, seaweed grows up to the surface like in the Sargasso Sea. If so, that seaweed could be harvested and dried into a building material. Perhaps its natural saps form a resin which make it almost wood-like once dried. So the harvesters pull it up, and lay it out in overlapping crisscrossed layers on open topped rafts. Need a one inch ...

12

You cannot have neither A or B. Of the two, B is the more implausible: the water is being pulled in 3 directions (up, right and down) by a single moon. About A, I would expect the two spheres (solid and liquid) to share the same rotation axis, and thus a non zero tidal height also on the side opposite to the moon, more or less like it happens on Earth. The ...

11

No. Not without another body getting involved. Tidal forces within the planet are constantly pushing it towards the "locked" state, you need a massive input of energy to change that. We're talking really dramatic events. You might be able to achieve something through a near encounter with a massive body (for example a large rogue planet passing through the ...

11

The book Seveneves has the moon break into 7 parts for no particular reason. It just broke; it did not blow up. The parts bump and grind into each other. A few weeks after it happens one big part breaks into 2 little ones and they break up more and more. One problem is the little parts of the moon that come down to earth. That actually turns out to be ...

10

Yes that sounds reasonable. Your moon has to stay out of the Roche limit in order not to get ripped apart. The Moon is ~ 400,000 km away, the Roche limit is only ~10,000km so you can move it closer. Having the moon closer to the planet will reduce the time it takes to orbit, the Moon orbits in 27 days, so 20 day orbital period sounds reasonable. Slightly ...

10

You can't achieve what you want with reality I should have explained this clearly when I first wrote the answer. I apologize for not having done so. I do not believe it is possible to achieve the effects you describe with reality. Moons large enough to create the tidal waves and the tidal shifts you're describing would make life on the planet miserable (...

9

Tides would be largely insignificant. Tides don't have much effect on ships in mid-ocean. The tidal forces of the moon pull the seas up by about 40cm. When this reaches land it causes flows which amplify the effect. If there is no land you just get a gentle 40cm rise and fall in the ocean every 12 hours. I doubt it would even be known by a pre-space age ...

8

The best real-world example to use here are the Inuit. They live in the coastal arctic, an area with no trees. However, they get around this by using driftwood that washes up on their shores. If trees are able to exist at least SOMEWHERE on this planet, then you can just have everyone do this. If there are no trees on their planet, have them use stone, coral,...

8

Yes, by radial mass redistribution. Something similar to the iron catastrophe on early Earth, or the melting of ice caps after ice ages. If something rises the internal temperature, it could trigger the migration of heavy materials towards the center of the planet, therefore reducing the moment of inertia and accelerating the rotation. As in the case of ...

7

All your settings are completely plausible. I upvoted the @ventsyv answer; but I need to correct one thing: Planets can rotate at any speed; in any direction; thanks to collisions during their formation. It is not mass dependent. Asteroids can spin like tops! See the NASA Planetary Fact Sheet, or for a more detailed explanation, see this more technical ...

7

I am afraid a moon cannot achieve what you are asking. Noticeable tides require noticeable water depth, and few meters excursion on few kilometers average depth do not leave the surface dry. If a moon would be so close to pull more the water bodies, the resulting tidal forces would quickly move it far away from the planet, reducing the tides. You can ...

7

The moon causes our tides, but not in the way most people believe. My answer below is belied by the this wonderfully detailed post, which explains exactly how tital forces playout, and debunks my ancient and cherished belief in how the tides actually worked. There is no tidal bulge Now from day to day, the moon doesn't move much (it takes just under 28 ...

7

Mangroves in an area with naturally high tides works Here is a mangrove forest in Kiribati at high tide: Here is one in Thailand at low tide: Mangroves are designed for this sort of enviornment. They are able to grow in salt water by diffusing all the salt that they suck in from their roots into sacrificial leaves, which are then shed. The next thing ...

7

Look at planet Earth: also there tides are extreme only when the Moon and the Sun (the main attractors when it comes to the tides) are aligned with the Earth. Approximately twice a month, around new moon and full moon when the Sun, Moon, and Earth form a line (a configuration known as a syzygy), the tidal force due to the sun reinforces that due to the ...

7

Why use wood? Umiaks and Kayaks have been made from whale and seal bones and skin. I see no reason why a sufficiently motivated population can't scale that up, perhaps using pontoon like structures, to larger structures. https://en.wikipedia.org/wiki/Umiak

7

An extremely powerful nearby pulsar that only hits one edge of the planet. While this is a rather "out-there" scenario, it's possible for a nearby, very powerful pulsar to repeatedly hit the planet during a small portion of its orbit, but only hit it on one side. This would impart a force to one side of the planet, slowly spinning it up over time the same ...

7

I'd also want the planet's orbit to stay roughly where it is - in the habitable zone. Does the planet have to start out in the habitable zone? If not, here's a suggestion, in a few stages, involving a gas giant on a very long period, comet-like elliptical orbit: Formation: have the planet initially form on a very close orbit to its star (on the order of ...

6

The tides are part of a balancing system If your flying island is actually continent-sized, the moon's gravity would affect parts of it at different times, causing it to rock or sway just a little, but enough to put serious stresses on the internal structure, reducing its lifetime. Whether by design or natural selection (all the other continents crashed ...

6

Quasi-magical mega-geyser There are plenty of geysers around, the most famous probably being Old Faithful which has been shooting about 8000 gallons of water into the air every 40-120 minutes since at least 1870. A little magic and imagination can extend a geyser principle to something large enough to affect a lake or inland sea. Your geyser is the lava ...

6

Tidal effects are based on how big something is and how far away it is. The Sun is pretty far away, but really big and thus has an effect on the tides. The Moon is not very big (on a planetary scale) but is pretty close and has an effect. Venus is bigger than the Moon, but much further away, and consequently has very little effect on the tides. This ...

6

It'd have to be pretty big. And by 'big', I mean instead of the moon orbiting the earth, the earth would become a satellite of the Moon. And the Moon would be around the size of Jupiter. I'm taking a guess from the context that the mechanism of uninhabitability that you're thinking about is tidal forces ripping the earth apart, or at least causing ...

5

Assuming that when you're talking about 'two moons adjacent to each other in a co-orbital configuration', you mean that a planet is being orbited by two moons, which are one gravitational unit in a binary configuration, something like a hierarchical trinary star system. I think it is very unlikely that something like this would ever form inside a solar ...

5

The scale of the tides exerted on one body by another can be calculated rather easily. (This is from Stephen Gillett's excellent book World-Building.) The formula is $$T = {M \over R³}$$ where $T$ is the tidal acceleration, $M$ is the mass of the body that exerts the tide, and $R$ is the distance between the two bodies. It is assumed that $R$ is much ...

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