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In a setting I am presently working on, I have envisioned a world similar to Star Wars' Takodana Star Wars' Takodana, in that its water is mainly in the form of large rivers, or smaller seas (I generally picture it being all rivers, unlike this picture; but I'm flexible). See also; Takodana's surface.

How realistic is this?

Fleshing out the question-

  • Would water erosion processes allow for all of the water to be separated, rather than being in an enormous, consolidated ocean that spans the world?
  • Could high geologic activity provide the necessary variance in altitude, or would that be in the benefit of oceans forming?
  • Would mesas be a prevalent feature in this landscape, or just hills and plains (as pictured here)?
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    $\begingroup$ I'm just going to leave this here. $\endgroup$ – Joel Harmon Jun 7 '16 at 3:46
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I think the current answers are all thinking of a very Earth like planet, including its orbit around its star.

As others have said, rivers have to flow somewhere, so your world would be more like full of seas or lakes than rivers.

How about we change things a little and have your planet orbit another, much more massive planet, such as a gas giant?

Get the giant in an orbit around a yellow star like our sun, and your planet will have as much sunlight as we do (though the gas giant may make for really interesting eclipses).

I am including the gas giant here because it will have tidal effects on the planet, much like the Moon does to Earth, but on a larger scale. Water will be pulled with extreme force towards the gas giant on the side that faces it, and away from the gas giant on the other side.

Now, if your planet is tidally locked, that water will be pretty much stuck. If not, your rivers will be pretty interesting, in that they will perpetually be running - but not necessarily towards the sea!

Huge edit @shufflepants has called my attention to the fact that the rivers wouldn't reverse their flow twice a day as I expected. So I am striking the previous text for this part of the answer, and including a couple scenarios that more probable, though still quite exciting.


In one scenario, your rivers could simple go around the world. On your planet, water will try to settle in the lowest places just like here on Earth. But there is no ocean, because there isn't a sea much below the river beds. Instead, the motive force behind the flow of the rivers are the tides. The tides will follow the gas giant, and the rivers will follow the tides. The interesting part is that this means the margins of the rivers will change within the course of a day. Some parts of the river may only be crossable by boat on the high tide, and may be crossable by foot on the lower tide.


Or, your planet could have oceans much like the earth. If it does, another interesting effect happens. You see, rivers end up in the oceans because usually they are more elevated than the sea. But during high tides, the water level on the sea may be higher, and the sea will go into rivers. When this happens on large rivers on Earth, the effects may be pretty... cinematographic, to say the least. In the Amazon river, the flow of the river is reversed in a five hundred miles strech starting where it meets the sea. Salt water enters the river in the form of waves that can be 12-feet tall at some points. This is what it looks like. You can surf on a single wave for more than half an hour!

This is technically called a tidal bore. There are dozens other places on Earth where this phenomenon happens. So you could just imagine that your world is an extrapolation of this, with these waves happening at least once a day for rivers that are to the east of an ocean (supposing your planet goes around the gas giant in the same way Earth goes around the Sun).


Both scenarios would give your planet interesting seasons. When the gas giant and the Sun rise together on the sky, or when the Sun and the gas giant are in opposite directions, the water of the high tide will be at its hottest ("tidal summer"?). But when they have a difference of 90°, you get the coldest high tide ("tidal winter"?)

As for geography of landmasses, it's up to you:

  • If the soil is very hard this movement of the rivers may act as a saw, digging ever deeper canyons on the land. So in high tides you get crossable rivers, but on the low tides you get deep ridges or fjords according to your worldbuilding taste.

  • If the soil is soft and will take the movement of the water, you can either have rolling hills or plains that get flooded in interesting patterns, or you can have places that look like tropical islands at high tide but look like deserts on the low tide.

You can also define how fast the water comes and goes... Depending on the force of the pull of the gas giant, the water may come slowly, or it may come like a tsunami (not very friendly to intelligent, surface dwelling life, though).

Also remember that your planet can have as many varied geographical features as real Earth does! You can mix all of the scenarios described above as you like.

One last thing, since I'm trying to be scientifically accurate here... Planets subjected to such tidal forces suffer from a special kind of geological effect because they are constantly being stretched in the directions towards and away from their "parent" planet. It is believed that this is what drives volcanism on Io (the most volcanically active place in the solar system). So your planet may be very active geologically too, if you want it to!

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    $\begingroup$ I'm not sure that this is realistic, but it's definitely cool. $\endgroup$ – user2727 Jun 7 '16 at 11:39
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    $\begingroup$ The tide mechanics here are pretty off. Assuming the entire flow is determined by tides, the river won't stop, and it won't reverse direction. There would be 2 "high tides" on the river per day. One when the gas giant is directly overhead, and one when the gas giant is on the exact other side of the moon. And if the planet is to be not tidally locked, this situation will have to have been a recent development with some hugely cataclysmic event introducing all the water at most a few million years ago or else the planet would have already become tidally locked. $\endgroup$ – Shufflepants Jun 7 '16 at 14:52
  • $\begingroup$ @Shufflepants thanks - I think that you are right in that. I remember having seen something like that before, I will look into it again and correct my post later today. $\endgroup$ – Renan Jun 7 '16 at 15:20
  • $\begingroup$ @Shufflepants I have made some changes to the post. While I do think that it is not 100% scientifically accurate, though, I think it is doable enough for a sci-fi or fantasy world. $\endgroup$ – Renan Jun 7 '16 at 16:39
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This is definitely realistic. What's actually interesting about this is that several of the issues you bring up sort of resolve each other. I'll go through them one by one.

In order to have this happen, you would need less water on the planet than Earth does. So right off the bat, even if you had an enormous consolidated ocean it would be smaller than the oceans of Earth. So right off the bat, you're going to be having less of an effect from erosion. Coupled with evidence from Earth, namely the Caspian Sea - which is completely landlocked - it's quite possible to keep the water separated.

There probably wouldn't be too much geologic activity. We currently think that large amounts of water are necessary for plate tectonics, that the plates formed by oceans leaving sediment until eventually the weight cracked Earth's crust. Since we don't have large oceans on your world, no plate tectonics, so less geologic activity.

Similarly, since we don't have very much geologic activity, there probably won't be mesas. Mesas are formed through eroding rocks uplifted by tectonic activity, so there would be fewer than on Earth, if any at all.

Speculation: One way I can see a planet like this developing is experiencing asteroid/meteorite impacts more frequently than Earth did. The way I see it, this would cause the planet to take longer to cool, meaning that the increased number of impacts would ultimately lead to a more pockmarked surface. When the planet does cool enough that liquid water can begin to build up, the craters would then become small seas. (Don't quote me on this part though, as I'm certainly no expert on planetary formation - I'm just extrapolating off what I know.)

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  • $\begingroup$ Wonderful answer- thank you! Might plate tectonics be influenced by external gravity sources, such as a moon; or would that friction be transferred into something else, with the lack of extensive water? The only problem I see with a lack of plate tectonics is the inability of a breathable atmosphere from forming. $\endgroup$ – user19838 Jun 7 '16 at 0:34
  • $\begingroup$ Again, just a (somewhat) educated guess as I'm not a geologist, but I would guess that extra heat generated from gravitational pulling would result in volcanoes around the planet, similar to Jupiter's moon Io. They would likely be more or less randomly scattered across the planet, not in major tectonic centers like Earth's Ring of Fire. I'm not sure what you mean about a lack of plate tectonics implying an unbreatheable atmosphere though. Is there a connection there that I don't know about? $\endgroup$ – John Robinson Jun 7 '16 at 1:07
  • $\begingroup$ OK, thanks again! I'm no geologist either, so I can't necessarily say that you're wrong or right- just present the information I've gathered. Yes, there is a connection between plate tectonics and atmospheric breathability, as during (Earth's) atmospheric evolution carbon dioxide is transferred into continental carbonate stores (I think... this is what Wikipedia says). So, without these plate tectonics I'm not sure what the carbon dioxide levels would look like- but I'll look into it. $\endgroup$ – user19838 Jun 7 '16 at 1:22
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The major issue I see is that rivers are flowing bodies of water. If the world was composed primarily of rivers and river systems, to where would all of that water be flowing? When the water reached its destination, what force would make it continue flowing? Gravity generally only works downhill, so I think to make a river world possible, it would have to extremely flat, effectively turning the rivers into canals.

Now, if a planet were incredibly massive, the gravity of such a planet may act to keep the planet flat (but flat enough, who knows?) For @John Robinson's idea of continued bombardment delaying the cooling to have an effect, the planet would have to have little to no atmosphere, creating an issue for the formation of life as we know it.

But an interesting thought I had is that the planet only has to be flat. That doesn't mean that it has to have been formed that way. Arguably, a sufficiently advanced (and motivated) society could flatten a world (realistically speaking, a smaller world than Earth) on purpose. Reasons for such a super-task might be the allocation of water to all parts of the globe/ populations; the facilitation of marine-based travel (the preferred mode of travel other than by foot for most of human-history); or self-preservation reasons like to control El Niño-type storm effects from a heating and cooling ocean, or to alter the planet's albedo for various reasons.

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    $\begingroup$ That is a wonderful point- and one that I was not entirely thinking of- thank you! However, what would prevent the river systems from simply flowing much like the ocean does; in currents dictated by tides? Concerning the lack/minimal atmosphere; also another good point that I have been trying to work around since @John Robinson posted his answer. The only thing I have come up with is the addition of atmospheric gasses through the bombardment of the planet, in respect to the second atmosphere of Earth (see Atmosphere of Earth Wikipedia article). However, I'm not sure how realistic that is... $\endgroup$ – user19838 Jun 7 '16 at 1:40
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    $\begingroup$ The acquisition of atmosphere during bombardment is not completely implausible. Some theories hold that Earth acquired its water via bombardment. And to your point, I suppose tides could cause the rivers to flow likes tides. That would actually solve the problem of stagnant water being generally undrinkable and disease-ridden. $\endgroup$ – Bryan Goggin Jun 7 '16 at 2:01
  • $\begingroup$ How about the terraformers are an amphibian race? $\endgroup$ – Loren Pechtel Jun 7 '16 at 4:34
  • $\begingroup$ When the riverflow is mandatory, you could consider integrating moons making in diferent angles periodically semi tides that construct a flow. $\endgroup$ – Zaibis Jun 7 '16 at 7:50
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Water erodes the land. Weather erodes the mountains, in general. Eventually this landform will flatten out. So, you need some geological mechanism to uplift the land with history that allows for the specific form that erodes into lots of rivers separated by harder rock.

It will be temporary, and probably only on part of the planet. Do you want it to be a common thing, with new such regions forming after old ones erode away? Or is it a one-time episode?

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You are showing a planet with massive lakes, consider the scale of the water features. Zoom out on google maps and see what water features we have that are on the same scale. Massive inland seas and the great lakes, not rivers.

So what you have is a fairly flat surface with few mountain ranges or evidence of tectonic activity, but still a fair amount of surface water. Perhaps the planet underwent planetary bombardment in the distant past which leveled the surface into a more uniform height (still lots of local elevation changes, but nothing like the deep sea to continental plateau elevations we have on earth). All the water on the planet was vaporized and re-condensed, raining down and being distributed in valleys.

These smaller "seas" can communicate with each other to some degree, circulation is primarily due to evaporation and rainfall. Without giant oceans and high mountain ranges, the surface of the planet is more uniform so weather patterns will be quite different (no sea currents to distribute temperatures, for example, or mountain ranges to stop rainfall). So the planet will have to be in a VERY sweet "goldilocks" zone to not freeze (an ice age will definitely carve up the terrain) or boil, thus it will probably be pretty tropical. Could even have a "tumbling" orbit so there are no polar regions and every part of the surface gets roughly the same amount of solar radiation to add to the uniformity of the entire surface (or perhaps a binary star system?).

Obviously this is not likely to be a "natural" planet, but one that saw intelligent intervention in the past that allowed it to develop life despite the circumstances that cause it to be a "river world" when seen from orbit.

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