Erm…I feel kind of lame asking a question with so many variables, and although I’ll try and give as much info. as possible, please don’t harangue me too harshly!
Any answers/theories proferred are gladly received.
There’s a planet and because of the speed of its rotation around its axis and its rotation around its sun, one side is permanently in the light, and the other permanently in the shade. I think this is reasonable so far - if not, I’m sure you’re aware of what I mean, and I’ll be grateful for the correction.
Assume the light-side of the planet is similar to Earth in all other respects but the light…so, vegetation, cloud cover, air mixture, distance to sun, all fairly similar to that of our very own planet. Even a moon (if that doesn’t cause any problem with the physics of all this).
If some parts of the above are not reasonable, ie. some aspects of this planet X simply CANNOT be like they are on Earth because of the nature of the planet, please mention them.
What would the weather be like on the light side?
What would it be like on the dark side?
What would it be like on the frontier between the two sides?
PS. In case you were wondering, this is for a sci-fi story that I’m considering writing. I’m not an astronomer (well, clearly) and I admit I don’t know too much about these kinds of things - that’s why I’m asking the dopers. I’m also a big fan of the BadAstronomers website and his sci-fi movie reviews, so I want to try and be reasonable accurate with my writing because I appreciate where he’s coming from.
Seems to me that the dark side, perpetually facing away from the sun, would get really damn cold. More than cold enough to freeze the oceans solid, and once frozen they’d stay frozen forever. Moisture in the air from the lit side would blow over the terminator and precipitate out as snow, which would fall, and then stay there forever, never melting. Before long all your planet’s water will have frozen on the dark side, leaving the lit size a parched and pretty much lifeless desert.
If that’s not bad enough, it’s concievable that the dark side might even get cold enough for the air to start freezing out. Now we repeat the above process until all the planet’s air is frozen on the dark side, and the lit side is now an airless and totally lifeless desert.
I don’t think a tidally locked planet could support life, unless there’s some mechanism to heat the dark side enough to keep all the volatiles from permanently accumulating there. Maybe a really active volcanic core to keep enough of the air and water melted out to support life?
IIRC, one of Poul Anderson’s van Rijn stories was set on just such a planet. I think AndrewL has got it mostly right that the light side would be searing desert while the dark side would be perpetually frozen. However, planetary orbits are elliptical, and a planet would tend to speed up as it goes to periastron. Conversely, the planet would slow down as it goes to apastron. Since the speed of rotation is constant, the terminator would slowly wiggle back and forth. This would allow weather and even seasons.
If it were apastron and you were standing on the equator just behind the terminator on one side of the planet (let’s call it the east pole), it would be winter - dark, cold, and frozen. As the planet revolves, you would see the sun slowly rise, warming the landscape and thawing out the ice. The sun will continue rising (though never moving far from the horizon) through periastron - its highest point and signalling summer. The sun would begin to set. This starts a cooling trend and ice will eventually re-freeze. Everything is reversed on the west pole, of course.
Stories about Mercury used toassume it was tidally locked like this (it turns out that it’s not – see any recent ref. on the length of Mercury’s day). IIRC, Stanley G. Weinbaum wrote a story about life in the “Twilight Zone” where libration caused a little variation in the sun’s position. There might be other Golden Age authors who did the same – check the Science Fiction Encyclopedia entry on Mercury.
Another possibility is Venus. She’s not quite completely tidally locked, but she’s getting there. Her dark side doesn’t freeze out because her thick atmosphere is adequate to transfer enough heat from the light side. Unfortunately, her thick atmosphere also turns her surface into a fair approximation of Hell. It’s to be expected, I suppose, of the goddess of love: From a distance, she’s beautiful, but get too close to her, and she’s a bitch ;).
I don’t know if it’s possible to get an atmosphere thick enough to equalize temperature without that temperature being hellish.
