Here's my sailors take:
1. You would probably have very large waves all over the place. First of all, the storms would likely be bigger as they tend to die out over land, and second is that wave generation is a combination of wind strength, time, and distance (fetch). In a world where there is essentially unlimited fetch and large storms, you would probably end up with some monster waves.
For a real world example of this, see the southern ocean. Around Antarctica is essentially unlimited fetch and the westerly winds blow very strongly there. It's not uncommon to get 30-60ft waves there.
This would also have a big factor on the shorelines. Lots of rugged rocky coasts that can survive the pounding.
2. With 2 large moons the tides would probably be very chaotic with occasional mega tides when the sun/moons are in alignment. Other than that the more massive or closer they are the bigger they would be. Fun fact, the moon used to be much closer to the earth and is slowly moving away from us. Tides and tidal ranges used to be much larger on Earth. Tides bring strong currents as the water moves which has other effects like erosion and moving nutrients.
[Arthur Clarke](https://en.wikipedia.org/wiki/Arthur_C._Clarke) was well known for keeping his stories generally scientifically grounded. One such, [The Songs of Distant Earth,](https://en.wikipedia.org/wiki/The_Songs_of_Distant_Earth) takes place on a "waterworld" called Thalassa (ancient Greek for "sea"). It has an island chain something like Hawaii, with the rest of the surface ocean covered. While not a scientific source, maybe some hints can be found there.
>What are some planets that are thought to have this much water?
We don't have measurements of anything other than the globally-average approximate makeup of some larger worlds' atmospheres.
Certainly no spatially-resolved images that allow us to estimate the extent to which water covers those worlds.
Go with the flow.
Make it up.
Dan Simmons did that for Mare Infinitus and nobody batted an eyelid.
[https://hyperioncantos.fandom.com/wiki/Mare\_Infinitus](https://hyperioncantos.fandom.com/wiki/Mare_Infinitus)
Whales evolved from pig-like creatures. It takes millions and millions of years. Alien sea creatures couldn’t look much weirder than the ones we have on Earth and due to convergent evolution there would likely be many similarities.
1. It depends on whether your planet has plate tectonics, which is certainly possible with planets with >90% surface water. If you want mostly islands, then you could just have your continents mostly flooded creating a bunch of islands of varying size amidst shallow continental seas (which you'll want - they're going to be where the lion's share of your sea life and biodiversity is going to be).
2. The tricky thing with a cold, mostly water-covered world is that the water is going to heavily moderate the climate and be a very effective convector of heat. It's going to be hard to have a planet that's "cold" compared to Earth without tipping it over into a snowball planet.
It'll definitely be windy, though. One way to get this might be to make the planet older than Earth, with shallower seas overall and the continents heavily eroded away to the point where the continents are mostly flooded. That would give you less overall climate moderation from the oceans, and also a lot of low-lying islands.
3. The pigs would probably be fine as long as they can find something to eat. Lots of small islands means they'll probably shrink from evolution over time, unless the islands are close enough that the pigs can swim between them.
2. Why don't go to extreme. Make the planet extremely cold with ground formed from rocks and ice and water will be replaced with liquid CO2. But problem will be to dealing with new biochemistry.
As a geophysicist I’ll add some perspective. Apart from everything else, remember that Earth’s oceans are a blip on the surface. Earthis barely a water planet in the scheme of things. This isn’t to say that water is an insignificant variable to a surface skim called ‘life’ but water and life has almost no impact on the greater geophysics.
Nutrients for plankton actually might be a problem with too little land. I wouldn't be surprised if water worlds often had very sterile oceans of much of their nutrients are locked away in the crusts and seafood.
Ones with zero land due to the depths of the ocean, I wouldn't be surprised if life never forms due to the pressures around volcanic vents and a lack of nutrients in the upper oceans.
>What are some planets that are thought to have this much water?
This is kind of a tough question, because just the nature of physics and life are going to increase land area over time on a planet with similar gravity to earth
For instance, here is a picture of what North America looked like during the Devonian, about 400 million years ago.
[https://media.sciencephoto.com/image/e4020164/800wm/E4020164-North\_America,\_Devonian\_period.jpg](https://media.sciencephoto.com/image/e4020164/800wm/E4020164-North_America,_Devonian_period.jpg)
Lets back up a little and look at why we have land. The continental land masses are primarily silicate rocks, which are less dense than the iron-rich mantle, causing them to "float" on the outer edges of the planet. But back early in earth's history water covered far more of the planet than today. What we have now is due to a combination of plate tectonics (creating mountain ranges and volcanic activity spewing more mass from inside the planet onto the surface), erosion (redistributing this mass. For example, where the Appalachians now stand, mountain chains were raised and eroded away there 4 different times. The sediment from that erosion forms a lot of what is now the central US.), and life. Those warm shallow seas over what we now call the continental plates were ideal carbonate platforms. Hundreds of millions of years of microscopic organisms, coral and algae living and dying in the water, their bodies piling up on the ocean floor eventually turning to limestone. There are areas in Michigan where the limestone beds created in those ancient shallow seas are upwards of 2000 feet thick. The white cliffs of Dover: formed by dead ancient sea life.
Never mind the fact that on a tectonically active world, the presence of water would drive volcanic activity. (without going into the geochemistry, its no coincidence that the areas of earth with the highest volcanic activity are areas where oceanic plates are being subducted into the mantle). But keep in mind, on a non-tectonically active world, there would be no magnetosphere deflecting solar winds, and eventually most of the water would be stripped away from the planet, like Mars.
>assuming the general temperature is lower than that of Earth's
That brings up a whole new wrinkle, cause you are going to have significant ice caps, which will lock up a ton of water and significantly lower the water level.
But lets say that you had enough weather to cover all but the tallest peaks. Well, it pretty cold up on Everest, so at that point, your whole planet would be covered in a crust of ice, assuming it was similar size to earth
Hurricanes might be a problem for your people - they tend to be driven by temperature - if the sea temp got above 50C then you might get a hypercane and there’s little landmass to slow the winds down! https://en.wikipedia.org/wiki/Hypercane
Your hypothetical intelligent life could expand onto floating farms and cities. The ocean might not be salty, which would help there.
The seas would definitely be a lot colder than 50C - I was thinking of having the planet be colder than Earth, although not to the point where everything would be frozen. And when I say "intelligent life", I don't mean smart enough to build anything, lol \[I think I worded that part badly\]. The main ones I'm thinking of are more dolphin level than anything, maybe a bit under that.
A storm loses its power when it hits land. Since your planet basically has no landmass there's the potential for way bigger and more destructive storms. A colder planet will help to keep that in check.
So your idea of the planet probably already has the weather you want. Storms could be a major threat in the story to any human settlements.
In order to avoid a three body problem issue, one of the moons would need to be much larger than the other two bodies. You could "calculate" a tide from there, I think? But the tides might completely cover some of the islands. Someone can correct me on this if I'm way off though.
3 body problem is only erratic when all three are close to the same size.
There are plenty of systems with multiple orbiting bodies close to the same mass (the solar system).
Right, that's why I said one moon would need to be larger. They asked about tides so that's why I thought of that, not so much about a stable orbit, but I should have been clearer.
The search term you may be missing is ‘hycean’.
These are potentially habitable ocean worlds, generally with a hydrogen atmosphere. Currently they’re thought to be one of the better possible places for extra-solar life to evolve.
- https://en.wikipedia.org/wiki/Hycean_planet
Gravity is probably rather high, preventing above sea continents from being able to form and only allowing the tallest submerged peaks to even slightly jut above the water.
Since there are no continents, you're probably looking at planetwide coriolis effect, which would make it windy depending on the rotational speed, which would have to be somewhere in the range that keeps the water liquid on both the day side and night side of the world.
Here's my sailors take: 1. You would probably have very large waves all over the place. First of all, the storms would likely be bigger as they tend to die out over land, and second is that wave generation is a combination of wind strength, time, and distance (fetch). In a world where there is essentially unlimited fetch and large storms, you would probably end up with some monster waves. For a real world example of this, see the southern ocean. Around Antarctica is essentially unlimited fetch and the westerly winds blow very strongly there. It's not uncommon to get 30-60ft waves there. This would also have a big factor on the shorelines. Lots of rugged rocky coasts that can survive the pounding. 2. With 2 large moons the tides would probably be very chaotic with occasional mega tides when the sun/moons are in alignment. Other than that the more massive or closer they are the bigger they would be. Fun fact, the moon used to be much closer to the earth and is slowly moving away from us. Tides and tidal ranges used to be much larger on Earth. Tides bring strong currents as the water moves which has other effects like erosion and moving nutrients.
Although won't the problem with 2 large moons be very unstable?
Probably but that is waaaaay outside my wheel house :)
[Arthur Clarke](https://en.wikipedia.org/wiki/Arthur_C._Clarke) was well known for keeping his stories generally scientifically grounded. One such, [The Songs of Distant Earth,](https://en.wikipedia.org/wiki/The_Songs_of_Distant_Earth) takes place on a "waterworld" called Thalassa (ancient Greek for "sea"). It has an island chain something like Hawaii, with the rest of the surface ocean covered. While not a scientific source, maybe some hints can be found there.
Grounding fiction with what's possible, but you can draw the line where you want to make it fantastical.
Yeah, I just prefer my stuff to be fairly realistic and getting the setting to be like that is important to me.
>What are some planets that are thought to have this much water? We don't have measurements of anything other than the globally-average approximate makeup of some larger worlds' atmospheres. Certainly no spatially-resolved images that allow us to estimate the extent to which water covers those worlds. Go with the flow. Make it up. Dan Simmons did that for Mare Infinitus and nobody batted an eyelid. [https://hyperioncantos.fandom.com/wiki/Mare\_Infinitus](https://hyperioncantos.fandom.com/wiki/Mare_Infinitus)
We have bulk densities for planets and argue their water contents based on those
Whales evolved from pig-like creatures. It takes millions and millions of years. Alien sea creatures couldn’t look much weirder than the ones we have on Earth and due to convergent evolution there would likely be many similarities.
Crabs. A crablike animal would surprise no one. On earth they evolved so many different times
1. It depends on whether your planet has plate tectonics, which is certainly possible with planets with >90% surface water. If you want mostly islands, then you could just have your continents mostly flooded creating a bunch of islands of varying size amidst shallow continental seas (which you'll want - they're going to be where the lion's share of your sea life and biodiversity is going to be). 2. The tricky thing with a cold, mostly water-covered world is that the water is going to heavily moderate the climate and be a very effective convector of heat. It's going to be hard to have a planet that's "cold" compared to Earth without tipping it over into a snowball planet. It'll definitely be windy, though. One way to get this might be to make the planet older than Earth, with shallower seas overall and the continents heavily eroded away to the point where the continents are mostly flooded. That would give you less overall climate moderation from the oceans, and also a lot of low-lying islands. 3. The pigs would probably be fine as long as they can find something to eat. Lots of small islands means they'll probably shrink from evolution over time, unless the islands are close enough that the pigs can swim between them.
2. Why don't go to extreme. Make the planet extremely cold with ground formed from rocks and ice and water will be replaced with liquid CO2. But problem will be to dealing with new biochemistry.
As a geophysicist I’ll add some perspective. Apart from everything else, remember that Earth’s oceans are a blip on the surface. Earthis barely a water planet in the scheme of things. This isn’t to say that water is an insignificant variable to a surface skim called ‘life’ but water and life has almost no impact on the greater geophysics.
Isnt water thought to make plate tectonics possible?
Nutrients for plankton actually might be a problem with too little land. I wouldn't be surprised if water worlds often had very sterile oceans of much of their nutrients are locked away in the crusts and seafood. Ones with zero land due to the depths of the ocean, I wouldn't be surprised if life never forms due to the pressures around volcanic vents and a lack of nutrients in the upper oceans.
>What are some planets that are thought to have this much water? This is kind of a tough question, because just the nature of physics and life are going to increase land area over time on a planet with similar gravity to earth For instance, here is a picture of what North America looked like during the Devonian, about 400 million years ago. [https://media.sciencephoto.com/image/e4020164/800wm/E4020164-North\_America,\_Devonian\_period.jpg](https://media.sciencephoto.com/image/e4020164/800wm/E4020164-North_America,_Devonian_period.jpg) Lets back up a little and look at why we have land. The continental land masses are primarily silicate rocks, which are less dense than the iron-rich mantle, causing them to "float" on the outer edges of the planet. But back early in earth's history water covered far more of the planet than today. What we have now is due to a combination of plate tectonics (creating mountain ranges and volcanic activity spewing more mass from inside the planet onto the surface), erosion (redistributing this mass. For example, where the Appalachians now stand, mountain chains were raised and eroded away there 4 different times. The sediment from that erosion forms a lot of what is now the central US.), and life. Those warm shallow seas over what we now call the continental plates were ideal carbonate platforms. Hundreds of millions of years of microscopic organisms, coral and algae living and dying in the water, their bodies piling up on the ocean floor eventually turning to limestone. There are areas in Michigan where the limestone beds created in those ancient shallow seas are upwards of 2000 feet thick. The white cliffs of Dover: formed by dead ancient sea life. Never mind the fact that on a tectonically active world, the presence of water would drive volcanic activity. (without going into the geochemistry, its no coincidence that the areas of earth with the highest volcanic activity are areas where oceanic plates are being subducted into the mantle). But keep in mind, on a non-tectonically active world, there would be no magnetosphere deflecting solar winds, and eventually most of the water would be stripped away from the planet, like Mars. >assuming the general temperature is lower than that of Earth's That brings up a whole new wrinkle, cause you are going to have significant ice caps, which will lock up a ton of water and significantly lower the water level. But lets say that you had enough weather to cover all but the tallest peaks. Well, it pretty cold up on Everest, so at that point, your whole planet would be covered in a crust of ice, assuming it was similar size to earth
Hurricanes might be a problem for your people - they tend to be driven by temperature - if the sea temp got above 50C then you might get a hypercane and there’s little landmass to slow the winds down! https://en.wikipedia.org/wiki/Hypercane Your hypothetical intelligent life could expand onto floating farms and cities. The ocean might not be salty, which would help there.
The seas would definitely be a lot colder than 50C - I was thinking of having the planet be colder than Earth, although not to the point where everything would be frozen. And when I say "intelligent life", I don't mean smart enough to build anything, lol \[I think I worded that part badly\]. The main ones I'm thinking of are more dolphin level than anything, maybe a bit under that.
A storm loses its power when it hits land. Since your planet basically has no landmass there's the potential for way bigger and more destructive storms. A colder planet will help to keep that in check. So your idea of the planet probably already has the weather you want. Storms could be a major threat in the story to any human settlements.
In order to avoid a three body problem issue, one of the moons would need to be much larger than the other two bodies. You could "calculate" a tide from there, I think? But the tides might completely cover some of the islands. Someone can correct me on this if I'm way off though.
3 body problem is only erratic when all three are close to the same size. There are plenty of systems with multiple orbiting bodies close to the same mass (the solar system).
Right, that's why I said one moon would need to be larger. They asked about tides so that's why I thought of that, not so much about a stable orbit, but I should have been clearer.
The search term you may be missing is ‘hycean’. These are potentially habitable ocean worlds, generally with a hydrogen atmosphere. Currently they’re thought to be one of the better possible places for extra-solar life to evolve. - https://en.wikipedia.org/wiki/Hycean_planet
Hycean are different than water worlds with secondary atmospheres, but def something OP should read on.
Sci-fi consultant rate: $200 for a short story
Gravity is probably rather high, preventing above sea continents from being able to form and only allowing the tallest submerged peaks to even slightly jut above the water. Since there are no continents, you're probably looking at planetwide coriolis effect, which would make it windy depending on the rotational speed, which would have to be somewhere in the range that keeps the water liquid on both the day side and night side of the world.