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Old 06-18-2009, 07:38 PM   #1
LazarusDarkeyes
 
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Default [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

Given: Through ANY extra-ordinary means (magical, divine, whatever), a planet rotates so that it has the exact same hemisphere of the planet always facing its sun. The axis of the planet's rotation is exactly perpendicular to the plane of its revolution around the sun. The pleny is otherwise Earth is all other respects (days per revolution, size, mass, distance from sun, 1 satellite orbiting which is the size of the moon, etc.).

Question: What would be the effects of this? Would one side of the planet be a desert, the other side a frozen wasteland, and there might be a ring around the planet which is intermediate and may actualyl be habitable?

Affect on oceans? Polar icecaps? Flora/Fauna? Atmosphere? Other?
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Old 06-18-2009, 07:45 PM   #2
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

Aurore from 2300ad (a ring of habitable area) or the home of the Proximans in Morgan Press' Terran Trade Authority RPG. More on the first as it is easier to consult...

In the case of Aurore the planet is in orbit of a gas giant, but the effects would be similar. There is what is called the High Desert, a temperate zone running though the poles and about the planet between them and a glacier on the other side of the world from the hot side desert.
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Old 06-18-2009, 07:52 PM   #3
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

What I know:
* Half the world would have perpetual day and the other half perpetual night
* There will be no seasons

What I guess:
* The dark side would have problems with plant growth and oxygen production; it would be colder
* The light side wouldn't be a desert
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Old 06-18-2009, 08:23 PM   #4
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

I believe that any habitable zone along the solar terminator will have constant strong winds blowing from the night side to the day side. (I think there will be a comparable counterflow somewhere in the upper atmosphere, but I have no idea at what altitude.)
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Old 06-18-2009, 08:29 PM   #5
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

Quote:
Originally Posted by LazarusDarkeyes View Post
Given: Through ANY extra-ordinary means (magical, divine, whatever), a planet rotates so that it has the exact same hemisphere of the planet always facing its sun. The axis of the planet's rotation is exactly perpendicular to the plane of its revolution around the sun. The pleny is otherwise Earth is all other respects (days per revolution, size, mass, distance from sun, 1 satellite orbiting which is the size of the moon, etc.).

Question: What would be the effects of this? Would one side of the planet be a desert, the other side a frozen wasteland, and there might be a ring around the planet which is intermediate and may actualyl be habitable?

Affect on oceans? Polar icecaps? Flora/Fauna? Atmosphere? Other?
In other words, a tidally locked planet.

Recent scientific studies suggest that, even when a world is tidally locked, heat would be transferred from the Day side to the Night side by oceans and the atmosphere.

GURPS Space actually covers such worlds. Using the rules in that book, the average temperature difference between Day and Night sides will be about 200 degrees. So...just a guess here...deserts (with forests in coastal regions) on the Day side and arctic wilderness on the Night side seems likely.
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Old 06-18-2009, 08:32 PM   #6
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

If the orbit is not perfectly circular, there'd still be seasons of a kind.

How the continents are laid out will make a difference. For example, if the sunward side has a large ocean, evaporation from this will create rainfall along its coasts, or if it's too hot for rainfall, still there could be clouds which change the temperature here and there.

The presence or absence of sizeable moons will make a big difference to the climate, too.
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Old 06-18-2009, 08:51 PM   #7
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

Quote:
Originally Posted by Mgellis View Post

GURPS Space actually covers such worlds. Using the rules in that book, the average temperature difference between Day and Night sides will be about 200 degrees.
That 200 degrees (which better be Fahrenheit) is a huge swing and obviously means that no more than one side of the planet has even a vague possibility of liquid water. If it runs 220 F on the day side and 20 F on the night side _neither_ side could have liquid water.

At Earth's distance from an equivalent star I think you need to write off the dayside. That side is likely to be much hotter than Earth and you'd have to be very lucky to keep it below boiling.

This is a big problem vis a vis photosnythesis. Nothing even remotely Earthlike is going live at an _average_ temprature above the boiling point of water. Even the extremophiles that live in the ocean floor's thermal vents straddle the transition zone and keep their average temp below boiling.

So I think the place is uninhabitable. With anything like Earth's amount of surface water it probably went runaway greenhouse with all the water vapor in the air. It might not be quite as a bad as Venus.

Even if it's not greenhouse I think you're looking at a non-oxygen atmosphere.
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Old 06-18-2009, 09:02 PM   #8
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

Quote:
Originally Posted by LazarusDarkeyes View Post
Given: Through ANY extra-ordinary means (magical, divine, whatever), a planet rotates so that it has the exact same hemisphere of the planet always facing its sun. The axis of the planet's rotation is exactly perpendicular to the plane of its revolution around the sun. The pleny is otherwise Earth is all other respects (days per revolution, size, mass, distance from sun, 1 satellite orbiting which is the size of the moon, etc.).

Question: What would be the effects of this? Would one side of the planet be a desert, the other side a frozen wasteland, and there might be a ring around the planet which is intermediate and may actualyl be habitable?

Affect on oceans? Polar icecaps? Flora/Fauna? Atmosphere? Other?
What you describe is a "tide-locked" world, discussed in GURPS Space on p. 125.

There would be a light side and a dark side to the planet. The light side would be warm, so its water would tend to evaporate and its air to rise. At high altitudes a warm moist wind would flow from light side to dark side, carrying patent heat, latent heat of evaporation, and water with it. This would warm the dark side as it cooled the lit side. The moisture would fall as rain and snow on the dark side, accumulating an icecap in the middle of the dark side. Sea levels would fall. But the transport of heat would be enough to prevent all of the water freezing out on the dark side. Glaciers, rivers, and ocean currents would transport the water back toward the light side, and cold fresh water would flow across the terminator from dark side to light (along with cold dry winds at low altitude). Ocean waters would become very saline in the middle of the light side: perhaps even forming mineral halide on the ocean floor.

The planet's rotation would be too slow to produce an appreciable Coriolis Effect, so winds would flow across, not along, isobars. There would be no cyclonic or anticyclonic winds or storms: no hurricanes, typhoons, or tornadoes.

Following the guidelines on p. 125 of GURPS Space I estimate that the proportion of Earth's surface covered with water would fall from about 70% to about 45%. Temperatures on the light side would average about 323K (121F) and on the nightside about 230 K (-45F).
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Old 06-18-2009, 09:58 PM   #9
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

I recall seeing a science program about scientific speculation concerning alien life (can't remember the name, though). One of the worlds described was a tide-locked world with a substantial ocean. On the spot on the planet closest to the sun there was the eye of an eternal hurricane that provided atmospheric circulation and a degree of heat transfer. I can't recall the details, but most of the life was around the edges of the hurricane.
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Old 06-18-2009, 10:44 PM   #10
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Default Re: [GURPS Space(/Fantasy??)] Consequences of a Unique Planetary Rotation

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Originally Posted by Mysterious Dark Lord v3.2 View Post
I recall seeing a science program about scientific speculation concerning alien life (can't remember the name, though). One of the worlds described was a tide-locked world with a substantial ocean. On the spot on the planet closest to the sun there was the eye of an eternal hurricane that provided atmospheric circulation and a degree of heat transfer. I can't recall the details, but most of the life was around the edges of the hurricane.
Sounds as though someone overlooked the Coriolis Effect.
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