## Could this planet exist?

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jewish_scientist
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### Could this planet exist?

I am writing a story where a planet has all the rivers going from North to South and the villain is redirecting the rivers so that they go South to North, leading to bad stuff happening. The obvious problem with this planet is that if all rivers meet at the South Pole, then how does the water get back to the rivers' source? The answer is simple. There is a really big tunnel that goes from the South Pole straight to the North Pole. How this formed is not important; Douglas Adams levels of weirdness is allowed encouraged. This leads to 2 less obvious problems.

The first is that if the water gets to its source without any work being done on it, then this planet is a perpetual motion machine. The second is that as the water falls, its potential energy is being converted into kinetic energy. Kinetic energy is basically temperature, so the water is getting REALLY hot. I do not know what happens to water when it gets hot enough to boil while free falling in a confined space and I will bet money that it is not good.

That I have figured out so far:
Spoiler:
The first solution I thought of is at the North Pole there is a huge Archimedes' screw that catches the water close to or near the point where all of its kinetic energy is transformed back into potential energy. It then caries the water up a significant distance vertically and empties it into the rivers. The biggest disadvantage of this solution is that it in no ways addresses the first problem.

My second solution is an Archimedes' screw goes from the South Pole to the North Pole. This solution limits the speed the water can travel, which puts a limit on the efficiency of the system. Another problem is that because the water is losing altitude, its potential energy must be decreasing; I am not sure what happens to this energy though. My guess is that it becomes mechanical force that makes the Archimedes' screw turn (which would be an advantage) or that the temperature of the water increases (which could be a disadvantage). If the potential energy becomes mechanical force, then it will do all the work required in order to make the the screw turn until the water reaches the height of the South Pole. This in turn [pun unintended] lowers the energy input of this solution to that of the first solution. This will also solve the problem of the water boiling. If the potential energy is converted to thermal energy, then the water may reach its boiling point while in a more confined space than in the first solution.

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ijuin
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### Re: Could this planet exist?

There is going to be friction in the water, both friction between the water and the screw and conduits, and turbulence within the water itself. For the scale that you are dealing with, you are going to need about a terawatt of extra energy input.

lorb
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### Re: Could this planet exist?

How about, the water falls to the center of the planet, and after that some more because kinetic energy. The core of the planet is hot and warms the water to become steam, which than rises up the other half of the journey? Maybe the tunnel is far wider at the north half than at the south half to allow for this.
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Sableagle
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### Re: Could this planet exist?

You have another problem to consider in this system: salinity.

I'd expect the increasing salinity of the water to reduce the rate at which minerals dissolve into it, so it wouldn't keep getting saltier and saltier like the Dead Sea, which is topped up by rivers that are fed rainwater and thus dissolve minerals from the catchment area. It would, however, get salty.
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gmalivuk
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### Re: Could this planet exist?

jewish_scientist wrote:The second is that as the water falls, its potential energy is being converted into kinetic energy. Kinetic energy is basically temperature, so the water is getting REALLY hot.
Kinetic energy in random directions is temperature, but kinetic energy all in one direction is just speed.

(Friction is what changes speed into heat.)
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Izawwlgood
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### Re: Could this planet exist?

What if you assumed an odd rotational period (precessing wildly and orbiting on a huge angle), wherein the 'north' pole is simply above sea level, and the 'south' pole isn't, and the 'south' pole gets more sunlight than the north, leading to lots of evaporation. This leads to condensation in the north, which runs south upon melting.

If you make a giant tube going along the planets rotational axis, I'd imagine you'd just get all the water accumulating in the middle? It's not like it's just going to flow from one pole to the other through this enormous tube, right?
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Nicias
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### Re: Could this planet exist?

You also could have the planet tidally locked. Then rivers would flow to the hot side, where they would evaporate, and condense on the cold side. It could be tidally locked to the sun or just be a moon of a warm gas giant, and tidally locked to that, so that the hot/cold was not that extreme.