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I mean, we experience tides here on earth because of combined effect of gravitational field of moon and sun. So I thought that tides could also occur on other planets.

Let us consider Neptune where the gas transits into a slushy ice and water layer. The water-ammonia ocean serves as the planet's mantle, and contains more than ten times the mass of Earth. Also it has 14 moons. What I was thinking was that more moons would mean more tidal effect would be seen even if distance from sun has increased.

But then I thought that the moons of Neptune would all have different orbits and different time periods of rotation. So this will definitely impact the extent of tides.

-To what extent will this affect tides?

  • And how will tides formed on Neptune be different than that formed on earth? I mean, how will they vary in properties?
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There will be tides, but they will be not very large. It's pretty easy to get a good estimate of their size.

There are two things that control tides on Earth and both will be present anywhere else: The tidal forces from celestial bodies, and the size of the body of liquid in which the tides are raised along with resonances int he body of liquid. Taking them in turn.

The tidal force is a bit funny, since the size of the tides raised on a planet by a celestial body is

(1) proportional to the mass of the celestial body raising the tide,

(2) inversely proportion to the cube of the distance away,

(3) inversely proportional to the surface gravity of the planet,

(4) and (roughly) proportional to the diameter of the body of liquid in which the tides are being raised.

That inverse cube of the distance means that the ability of a body to raise a tide drops off very quickly with distance.

Comparing Earth and Neptune: The Sun is 30 times further from Neptune than Earth, so Solar tides will be roughly 27,000 times smaller on Neptune. They can be completely ignored.

Triton (Neptune's largest moon) is the jackpot, since it's a third as massive as Earth's Moon, and about the same distance away. Neptune is 17 times more massive than Earth and four times the diameter. So Triton tides of Neptune will be about fifteen times smaller than lunar tides on Earth.

All the other moons are much smaller or further away or both and will raise completely negligible tides.

So from gravitational effects alone, Triton will raise small tides and nothing else will be measurable without good instruments and a lot of care.

(Note, I'm talking about tides in oceans comparable in size to the planet -- for smaller bodies of liquid, the tides will scale down.)

On Earth, tides vary all over the place, and this is due to the configuration of the body of water and resonance effects. Basically, if a body of water has a resonance -- a natural period for sloshing back and forth -- that matches the period of the tidal force, the tide can build up like repeated pushes to a kid in a swing.

Additionally, there can be a funnel effect with two arms of land coming together, or shallowing water that can amplify the tides. (E.g., the Bay of Fundy.) Since as far as we know, Neptune has no land, it's effectively an planetary ocean and will get the full effect of the gravitational tides, but no resonances.

So, bottom line: Small Triton tides and nothing else.

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    $\begingroup$ Thanks for this Mr. Mark. This helped. But one more doubt emerged in my mind while reading your answer. Do neighbouring planets affect tides ? $\endgroup$ – Garima Feb 2 at 16:19
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    $\begingroup$ Sure, but they are very, very small effects because of the inverse cube of the distance. $\endgroup$ – Mark Olson Feb 2 at 16:25
  • $\begingroup$ Minor nit - if a putative Neptune-sized planet had "oceans" of some low-density fluid, the physical effect would be greater than for, say liquid water. Otherwise, nice clean explanation. $\endgroup$ – Carl Witthoft Feb 5 at 15:04

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