Weather conditions an a tidally-locked planet.

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Weather conditions an a tidally-locked planet.

Postby billiamo » Tue Jun 30, 2009 10:12 am UTC

If there was a planet like Earth, orbiting a star like the Sun, but in a tidally-locked orbit, what weather conditions would arise?

By Earth-like, I mean that it is at a similar distance, is similar size and mass, has a similar atmoshperic composition and similar ratio of sea to land on its surface.

So one side will be facing the star at all times, and the other side will never be in direct sunlight. There will still be rotation, but it will be a lot slower than on Earth, and that would mean the Coriolis effect would be a lot less powerful.

What other factors would affect weather here, and what kind of weather would we see?
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Re: Weather conditions an a tidally-locked planet.

Postby Velifer » Tue Jun 30, 2009 1:32 pm UTC

Two massive Hadley cells?
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Re: Weather conditions an a tidally-locked planet.

Postby [Kreativername] » Tue Jun 30, 2009 8:55 pm UTC

Well I think the biggest effect would be that over time all the water on the brighter side would evaporate and snow down on the dark side. There it would just lie around never coming back (sublimation should be negligible). So the brighter side would be extremely dry and hot and the darker side would be almost completly frozen.

Then it would get worse.

In the absence of liquid water most types of weathering that we observer on earth and most importantly carbonation (my first post*) wouldn't occur. That would allow gigantic amounts of carbondioxide from vulcanic activity to build up in the atmosphere thus creating a massive greenhouse effect. At this point there is a silver lining though and it's not from evaporated lead either. Before the trapped heat builds up to Venus like levels some of the ice on the darker side starts melting, finally allowing some carbonation to happen. Over time the whole process of "ice melting allowing carbonation to happen" vs "new carbondioxide being added by volcanoes" should balance out and somewhat stabilize the surface temperature. There would then be some lakes/oceans presumably at the edge between the bright side and the dark side under an everlasting sunset where live could actually develop.

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Re: Weather conditions an a tidally-locked planet.

Postby Zhatt » Tue Jun 30, 2009 9:30 pm UTC

At that range, wouldn't the surface on the sun-side become molten? The molten rock would slowly work its way to the edge where it could cool and then get pushed back under in a large subduction zone? Mountains might build up along the edge where lighter rock doesn't sink.
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Re: Weather conditions an a tidally-locked planet.

Postby gmalivuk » Tue Jun 30, 2009 9:51 pm UTC

Why would the surface be molten?

I know it's not tidally locked, but Mercury's isn't and it's a lot closer to the sun.
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Re: Weather conditions an a tidally-locked planet.

Postby InkL0sed » Tue Jun 30, 2009 9:56 pm UTC

I don't think a tidally-locked Earth sounds like a good plan in any case.
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Re: Weather conditions an a tidally-locked planet.

Postby [Kreativername] » Tue Jun 30, 2009 10:37 pm UTC

InkL0sed wrote:I don't think a tidally-locked Earth sounds like a good plan in any case.


Maybe, but I like the whole "everlasting sunset" thing. Although I could probably have that in the polar regions of a rotating planet with a non tilted axis so lets try that first.

I think the observed surface temperatures on the (very slowly rotating) moon make a good estimate of what surface temperatures on a tidally-locked earth would look like. Quote Wikipedia:
"During the lunar day, the surface temperature averages 107°C, and during the lunar night, it averages -153°C"
So even a strong greenhouse effect probably couldn't bring the temperature into the melting-rock-range before the temperature starts to stabilize due to increased weathering.
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Re: Weather conditions an a tidally-locked planet.

Postby SlyReaper » Wed Jul 01, 2009 10:29 am UTC

By my understanding, the daylight facing side would quickly deteriorate to desert-like conditions, and the night side would freeze solid. The day-light terminator would be ravaged by titanic storms for a while until all the water in the atmosphere had frozen on the night side.
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Re: Weather conditions an a tidally-locked planet.

Postby Velifer » Wed Jul 01, 2009 4:38 pm UTC

But with the surface heating at the hot side, warm air would rise. This would cause the cooler air from the sunset and dark areas to move along the surface, likely bringing moisture with it. The uplifting air at the hot side would cool as it rose, likely leading to precipitation.

Look for a place where those winds have to flow up over a mountain, and live on the "wet" side of that range. Then you can benefit from the rain without living in eternal high noon.
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Re: Weather conditions an a tidally-locked planet.

Postby InkL0sed » Wed Jul 01, 2009 5:51 pm UTC

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Re: Weather conditions an a tidally-locked planet.

Postby [Kreativername] » Wed Jul 01, 2009 8:34 pm UTC

Velifer wrote:But with the surface heating at the hot side, warm air would rise. This would cause the cooler air from the sunset and dark areas to move along the surface, likely bringing moisture with it. The uplifting air at the hot side would cool as it rose, likely leading to precipitation.


And still over time all the water would probably end up frozen on the dark side. Most of the water that is transported to the dark side might fall down in an area where it is not so cold that the water would be permanently frozen and that water could make it's way back to the warmer side where it would evaporate again. So yes initially the water would circulate back and forth. There would however be regions deep on the dark side where it's cold enough for the water to remain frozen permanently. If just a tiny fraction of the water would fall in those regions then with each circulation the planet would get drier and the ice sheet would grow. And over time all the water would accumulate on the dark side leaving the rest of the surface dry.

At least until the greenhouse effect I described above kicks in and melts away a big portion of the ice.
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Re: Weather conditions an a tidally-locked planet.

Postby Zhatt » Thu Jul 02, 2009 6:37 pm UTC

If just a tiny fraction of the water would fall in those regions then with each circulation the planet would get drier and the ice sheet would grow. And over time all the water would accumulate on the dark side leaving the rest of the surface dry.[/quote]

Wouldn't all the ice on one side of the planet be enough weight to unbalance the planet and "un-lock" it? If I remember correctly, a locked body has it's heavy side to the body it's locked to. That is the moon's heavy side always faces earth.
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Re: Weather conditions an a tidally-locked planet.

Postby Carnildo » Fri Jul 03, 2009 3:00 am UTC

Zhatt wrote:Wouldn't all the ice on one side of the planet be enough weight to unbalance the planet and "un-lock" it? If I remember correctly, a locked body has it's heavy side to the body it's locked to. That is the moon's heavy side always faces earth.

Keep in mind that the planet always rotates around its center of gravity, and moving ice moves that center of gravity, so you can't 'unbalance' it. A tidal lock is stable so long as the planet has as much weight orbitally ahead of the line from its center to the primary as there is behind it: you can move ice to the polar caps, the light side, or the dark side without breaking the tidal lock. If you were to move the ice to the leading hemisphere, however, the planet would start rotating until the ice was in line with the primary.
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Re: Weather conditions an a tidally-locked planet.

Postby Sockmonkey » Sun Jul 05, 2009 1:37 am UTC

If the glaciers advanced into the temperate zone as fast as ice accumulated then you could see some stability.
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