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RalofTyr
2008-Feb-21, 01:05 AM
If an Earth-like world were tidally locked to a more massive gas giant, a moon basically, where would the water flow?

Since the more massive side is always facing the gas giant, wouldn't that mean water flows away from the gas giant, or would the tidal stress pull the water towards it?

Jerry
2008-Feb-21, 01:48 AM
'Tidally locked' implies the earth has been in orbit about the gas giant for a very long time. The liquid water, if there is any, would be in orbit too, distributed about the planet, but pulled closer to it on the side facing the planet, and shallow on the opposite side.

The reason that the tide on earth rises on both sides of the planet is because the rotation creates a dynamic situation - the earth oscillates within the oceans. If the earth were tidally locked in rotation, (and asside from the effects of other bodies), The fluid about the earth would settle into gravimetric equalibrium, and the weakest gravitational force relative to the center of the earth would be in the middle of the side facing the gas giant.

Noclevername
2008-Feb-21, 01:53 AM
Actually, it would be pulled to both sides-- one bulge toward the larger planet, and one away from it. Tide results from differing levels of orbital energy, not direct pull.

01101001
2008-Feb-21, 02:22 AM
Actually, it would be pulled to both sides-- one bulge toward the larger planet, and one away from it. Tide results from differing levels of orbital energy, not direct pull.

Yeah, I'd have to think it's somewhat like watery Earth now, in relation to the moon, even though Earth is not locked to the moon and is still rotating itself through and under the two bulges.

But, if the Earth-sized body was the small one, no doubt the two bulges would be relatively ginormous.

cress
2008-Feb-21, 02:30 AM
There would still be a tide associated with the Sun, but it would be a feeble thing in comparison to the twin bulges.

If we were part of a system like the Galilean satellites, they might also create a very weak system of tides, but it'd be a much more complicated one.

01101001
2008-Feb-21, 02:35 AM
It occurred to me to think of the Moon as is, not a body coated with any liquid water, but a body that is nonetheless slightly flexible and able to flow a little.


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Well, the Earth's gravity also affects the Moon. It distorts the Moon's shape slightly, squashing it out so that it is elongated along a line that points toward the Earth. We say that the Earth raises "tidal bulges" on the Moon.

hhEb09'1
2008-Feb-21, 03:41 AM
The reason that the tide on earth rises on both sides of the planet is because the rotation creates a dynamic situation - the earth oscillates within the oceans. If the earth were tidally locked in rotation, (and asside from the effects of other bodies), The fluid about the earth would settle into gravimetric equalibrium, and the weakest gravitational force relative to the center of the earth would be in the middle of the side facing the gas giant.That's kinda what Galileo thought, which is one of the reasons he got in trouble :)

The two bulges on the earth have nothing to do with rotation, it is just the differences in the pull of gravity with distance.
There would still be a tide associated with the Sun, but it would be a feeble thing in comparison to the twin bulges.Not that feeble.

The tidal effect due to the sun is about half that due to the moon. When they line up together, we get one and a half, the spring tide. When they are ninety degrees apart, about twice a month, the solar tide negates the lunar tide and we get a half, the neap tide. So, the solar tide alone would be about like our current neap tides.

It occurred to me to think of the Moon as is, not a body coated with any liquid water, but a body that is nonetheless slightly flexible and able to flow a little.Because of lunar libration, the earth tides on the moon shift some, and the shift causes moonquakes that have been detected by seismometers on the moon.

Hornblower
2008-Feb-21, 04:14 AM
Suppose we could somehow eliminate the Sun's tidal effect while keeping the ocean liquid. Here is what I think would happen.

The solid body of Earth is not totally rigid. If tidally locked, it eventually should settle into the same equipotential shape as the overlying water, leaving very little bulging of the water with respect to the bottom.

Before the solid body reaches that state, the water should bulge toward the large planet on the side facing it, and away from the planet on the other side, just as it does with our familiar tides. I am confident in my opinion that Jerry is mistaken.

hhEb09'1
2008-Feb-21, 04:41 AM
That is mostly true. Even today, the earth deforms daily--if it did not, the tides would be greater than they are now. If the "earthtide" were greater, the tides might even disappear, in the sense that they would not be noticed at a wharf or beach.

tony873004
2008-Feb-21, 09:29 AM
We'd probably would have never notice tides, until we had the technology sensitive enough to measure how much Earth deviates from a sphere.

In a general every-day sense, we think of tides as the cyclical changing of local sea level. If it were permanantly high tide or low tide in a locality, the residents wouldn't realize that. They would just see their unchanging water level.

cress
2008-Feb-21, 09:43 AM
Not that feeble.

The tidal effect due to the sun is about half that due to the moon. When they line up together, we get one and a half, the spring tide. When they are ninety degrees apart, about twice a month, the solar tide negates the lunar tide and we get a half, the neap tide. So, the solar tide alone would be about like our current neap tides.
Yes, it wouldn't be that feeble in an absolute sense, and you wouldn't need specialist equipment to notice it. But as you say, the tide from the Sun is about half as strong as that of the Moon. If we replaced the Moon with Jupiter, which is about 26,000 times more massive, then it would be a heck of a lot smaller in comparison.

Celeste
2008-Feb-21, 09:53 AM
Yes, it wouldn't be that feeble in an absolute sense, and you wouldn't need specialist equipment to notice it. But as you say, the tide from the Sun is about half as strong as that of the Moon. If we replaced the Moon with Jupiter, which is about 26,000 times more massive, then it would be a heck of a lot smaller in comparison.

If Earth was tidally locked to Jupiter then the gravity tide from Jupiter would just cause two stable bulges on opposite sides of the planet but no apparent sea (traditional and first meaning) tide. So the tide from the Sun would be noticed.

cress
2008-Feb-21, 10:29 AM
I thought that was what I said (taken in conjunction with my first post above)? Or maybe I'm just not explaining myself very well, sorry.

Anyway, while I'm here again I just checked the numbers and for a Galilean-type orbit, the tide raised by Jupiter would be about three and a half thousand times stronger than the tide from our Moon. Which has got me curious about how much the liquid tides raised from the Sun would compare to the (stationary) solid tide raised by Jupiter, if anyone would like to check the numbers...?

mugaliens
2008-Feb-21, 03:16 PM
'Tidally locked' implies the earth has been in orbit about the gas giant for a very long time. The liquid water, if there is any, would be in orbit too, distributed about the planet, but pulled closer to it on the side facing the planet, and shallow on the opposite side.

er... Don't tides swell on both sides of the axis between Earth's center of mass and the center of mass of the Moon, Sun, and or massive gas giant?