Gliese 581g - A Tidally Locked DnD World

[Alaxk Knight of Galt]

So Gliese 581g was found. Scientist believe it to be Tidally Locked (much like the moon). One side of the planet is constantly facing the star while the other side of the planet would be in darkness. A swath of the world would always be in a state of continual sunrise or sunset.

So here's the thought exercise: What would a DnD tidally locked world be like?

 

[possum]

Look at how the planet Ryloth was depicted in the Star Wars expanded universe prior to the Clone Wars tv series screwing it up. The majority of society lives in the narrow band of perpetual twilight buffered against the freezing cold half of the world that faces away from the sun and the blazingly hot half that does. This society is probably underground, as sometimes flame storms from the hot side trespass into the habitable band, and I wouldn't be surprised if the opposite is true with the cold half.

Thank you, Kevin J. Anderson.

Now, as for some plots; there's always some evil wizard worshipping the giant sun who wishes for it to reign supreme and will attempt some ritual to wipe out all life on the planet thanks to the flame storms.

There's also the good-intentioned mages or druids who will attempt to get the planet moving on a normal basis, which will naturally destroy all society and maybe even the planet itself.

 

[Festivus]

Dark Side: Cold and Dark. The creatures that lived there before the world stopped turning either adapted to the extreme cold (lots of fur or blubber) and have night vision or some form of illumination, or died and rose again to become undead. Look to deep sea life here on earth, or drow for inspiration... so almost like the underdark on the surface, only set in Antarctica. Plant life evolved into mushrooms, glowing lichens and other assorted things that don't require light (even perhaps carnivorous plant life)

Light Side: Hot and Arid, Far to bright to see. The creatures that lived there before the world stopped turning either adapted to the environment or died and rose again to become undead. Imagine "Dark Sun", only hotter. Survival in the desert is nearly impossible for anyone considered normal.

Between the two of these realms is a swath of life that has a day that wobbles between sunrise and sunset, neither taking much time to accomplish. Life in this belt flourishes. The creatures the lived there before the world stopped turning had no need to adapt, but must now continually defend themselves from the marauders from the light and dark sides of the planet.

 

[jonesy]

Look at how the planet Ryloth was depicted in the Star Wars expanded universe prior to the Clone Wars tv series screwing it up. The majority of society lives in the narrow band of perpetual twilight buffered against the freezing cold half of the world that faces away from the sun and the blazingly hot half that does. This society is probably underground, as sometimes flame storms from the hot side trespass into the habitable band, and I wouldn't be surprised if the opposite is true with the cold half.

Thank you, Kevin J. Anderson.

That's reminiscent of a planet whose name I can't remember from the Foundation series. Which makes sense, since Isaac Asimov was a huge influence on Anderson.

 

[Umbran]

Dark Side: Cold and Dark.

...

Light Side: Hot and Arid, Far to bright to see.

I'm approaching this by way of applying some basic science to the thing: since it is a fantasy world, science doesn't have to apply, of course.

Being tidally locked does not make the sun brighter on the day side. It is merely more persistent. The brightness in the center of the hot side is still only what it would be at Noon if the planet were spinning.

Also, Gliese 581, our example, is not like our sun. It is a red dwarf, far smaller, dimmer, and cooler than our star. The back-of-the-envelope estimates I've seen suggest that, if the planet had an Earth-like atmosphere, you might see high temps of around 160 degrees Fahrenheit on the day side, and -25 on the night side.

The habitable band around the terminator between night and day, then, is probably pretty wide, as even the hottest and coldest points aren't all that hot or cold. There are no fire storms - 160 degrees isn't hot enough to ignite most materials. Water tends to evaporate quickly, but it doesn't outright boil. The cold.. well, -25 is something that folks in the Northern US see not too infrequently.

Another thing you'll see: persistent wind. On the day side air is heated, and will rise. Cooler air from the night side will be sucked in to replace it. So, near the ground, you get winds flowing dark to light, and up high you get flow from light to dark. This convective mixing may mitigate the temperature difference significantly. Storm patters would not be much like what we see on Earth.

 

[jonesy]

How about creatures (perhaps intelligent) born on the central band which have now adjusted to both extremes. They spend time basking in the sun of the hot side, and then go on hunting trips in the cold side (perhaps because they find the hot side creatures inedible for some reason).

 

[Festivus]

I'm approaching this by way of applying some basic science to the thing: since it is a fantasy world, science doesn't have to apply, of course.

Being tidally locked does not make the sun brighter on the day side. It is merely more persistent. The brightness in the center of the hot side is still only what it would be at Noon if the planet were spinning.

Also, Gliese 581, our example, is not like our sun. It is a red dwarf, far smaller, dimmer, and cooler than our star. The back-of-the-envelope estimates I've seen suggest that, if the planet had an Earth-like atmosphere, you might see high temps of around 160 degrees Fahrenheit on the day side, and -25 on the night side.

The habitable band around the terminator between night and day, then, is probably pretty wide, as even the hottest and coldest points aren't all that hot or cold. There are no fire storms - 160 degrees isn't hot enough to ignite most materials. Water tends to evaporate quickly, but it doesn't outright boil. The cold.. well, -25 is something that folks in the Northern US see not too infrequently.

Another thing you'll see: persistent wind. On the day side air is heated, and will rise. Cooler air from the night side will be sucked in to replace it. So, near the ground, you get winds flowing dark to light, and up high you get flow from light to dark. This convective mixing may mitigate the temperature difference significantly. Storm patters would not be much like what we see on Earth.

I mistyped that, meant to say "far too bright to see without sunglasses" or similar optical evolutions.

I like the persistent wind thing, but for every action, there is an equal and opposite reaction. Perhaps the weather pattern pushes moisture to the cold side, feeding it's glaciers. The planet has a molten core which melts the underside of the galciers, which drips down through a massive honeycomb of caves to the molten core, where it evaporates to a gas and extrudes from the light side. I dunno, something like that

I agree the belt would be pretty wide, not unlike the tropic of cancer / capricorn in terms of width, but with the temperatures getting extreme to the edges of it. While still habitable, people in the north of the US don't endure a year of -25f temps, there are seasons. But then, if the year were shorter, it could be different.

Oh this is fun.

 

[Huw]

Brian Lumley's vampire planet in the Necroscope series had one side permanently facing the sun and the other (where the vampires live) away. I think that one actually span on its side, like Uranus in our own solar system, rather than was tidally locked with its star.

 

[possum]

That's reminiscent of a planet whose name I can't remember from the Foundation series. Which makes sense, since Isaac Asimov was a huge influence on Anderson.

I have sadly not read that. I'll see if I can find a copy at my library.

 

[jonesy]

I've just been told by my girlfriend that I'm totally wrong and don't know what I'm talking about.

Not about the Asimov influence. That's true.

But the planet I was thinking of was warm on the equator (which rotated straight towards the sun), and everything else on the planet was iced.