Gliese 581g - A Tidally Locked DnD World

[Festivus]

The process of becoming tidally locked will generally force the axis of rotation to be perpendicular to the plane of the orbit. You can have some small wobble, but nothing like the 23.5 degrees Earth has.



Actually, it won't be, in general. A tidally locked body will be elongated - with a long axis along the line between the centers of the bodies. So, like an egg, one end pointed at the star.



Well, now you're talking about a shape that couldn't develop by real-world natural processes. Magic is involved, so all bets are off!

What if the hole was blown into the center of the world by some evil plot long ago, rendering the world into it's current state (torus shaped and spinning like a wheel in it's orbit around the sun). Or if the planet was pierced by something else that managed to not totally destroy it.

 

[I'm A Banana]

Yeah, you're going to see the most difference with weather patterns, nocturnal/diurnal evolutions, and suchlike. Depending on the plate tectonics such a world has, as well, you could see pretty even temperature distribution.

What strikes me would be the wildlife.

Say, there is a continent on the Dark Side, basically isolated from the Light Side (especially seeing as winds would make it a little more difficult to do some migratory flying like birds do here). Why would creatures there need eyes? Or color? Imagine fish in those ice-locked oceans. Imagine the sloooooow metabolism of creatures over there. I mean, there'd be no plants -- no photosynthesis as we know it. But with some volatile plate tectonics there could be interesting chemosynthesis. Worms and bacteria and insects and fungi in a frozen world that never sees the light of day. GIANT things that feed on them, slowly, over aeons.

Of course, the other side would be made with photosynthesis (assuming that it's not a unique Earth evolution). Rampant plant life. Rampant life in general -- heat and light and an explosive orgy of bugs and bacteria and fish and maybe even more complex life. After all, it may not have been coincidence that the first "sapient" life on Earth evolved along the equatorial line.

 

[ajanders]

Random Musings

There won't be much astronomy on the light side. The dark side might have societies with intimate knowledge of the stars.

Societies on the light side could expand into the dark, with sufficient technology. Get a giant mirror high and you can reflect the sunlight onto the dark. You can hang it from a kite or balloon (if you have a strong tether) or put it atop a big tower. The sun won't be moving as much, so it should be relatively easy to track.

Can a big mountain create a pocket of shadow on the light side?

A big mountain (really big) might create a rainshadow on the dark side and a rainfed water cycle on the light side. This is probably a pretty good spot for people to live.

 

[Lanefan]

Which brings me to another note - unless there's a major moon or other body that drives a periodic change, this planet does not have "seasons", as we understand them. The climate would have weather, but otherwise be "steady state" over the course of the year.

There's some other variables to consider:

How much water does this planet have, and where is most of it (e.g. light side, dark side, both)? (this would drive weather patterns)

Where is the land and how is it distributed? (ocean currents, if they exist, also drive weather and are a big transporter of heat/cold)

How much atmosphere is there, and how much cloud cover? (more of either means less temperature variance between light and dark sides)

I've been giving this some serious thought of late, mostly along the lines of what would happen to a world's weather if its axis had no tilt; and I suspect it'd be much less variable than ours in any given place even beyond the obvious removal of seasons; because so much of our weather is driven by trying to redistribute the uneven seasonal heating we get. If the planet's truly locked *and* with no tilt to its axis I think the weather patterns would also almost lock in - there'd be places where it's always sunny but 50 miles away there'd be endless rain...

Lanefan

 

[Stormonu]

Getting away from science for a moment, you could have some interesting methods of "lighting" the dark side if you did not want perpetual night for some reason, or "points of light" (pun intended) in the darkness.

As I previously stated, you could have bioluminescant creatures.

Heavy (ashless) volcanic activity could provide a source of light/heat.

Constant thunderstorms from the mix of cold/hot air may light areas of the dark side in random flashes.

A orbitally locked moon that reflects light down to the land below.

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Similarly, you could have periods of "darkness" on the light side that provide protection from the glaring sun or "areas of darkness" (pun intended) to adventure in:

Heavy cloud cover/fog from rising water vapor obscuring the light

Regular eclipses from a quickly orbiting moon (Imagine raiding creatures from the night side following the path of the eclipse to attack settlements in the light side...).

Chasms, craters or other features angled just right to provide protection from the sun

 

[Merkuri]

I'm imagining a world with life stacked on one side, steaming jungles with plant life so thick in places that you need to tunnel through it or climb over it to travel.

Civilization lives in the narrow band of twilight, the sun being a constant spot on the horizon, an unerring point of reference, like our north star.

And the other side, which lives in an underdark-like state of blackness except for the glowing sky, alight with stars that could not be imagined on the jungle side. It is silent and dead. The little bit of life there is on this side of the world is made up of super stealthy predators. It is eat or be eaten on the dark side. They only way for life energy to make its way around from the sun is through creatures stupid enough to wander their way into the black and be consumed.

The sun side draws the civilized folk because it's teeming with wood, exotic foods, spices, and medicinal wonders.

The star side might draw civilization because of the stars themselves. It is a religious experience for these people to see the spots of light on that side of the planet. Maybe they believe that both sides of the planet had a sun at one time, but some godling shattered the one on the dark side, and that the stars are the dust that was left over.

Or maybe the star side is rich in minerals or other wonders just below the surface, something that is impossible to reach under the thick plant life of the jungle side. Metals and gems just sit on the surface of the dark side with no plant life to anchor the soil, but silent death waits among the stars for those who try for it.

Damnit, now I wanna scrap my old idea for a campaign setting and use this instead.

 

[Umbran]

What if the hole was blown into the center of the world by some evil plot long ago, rendering the world into it's current state (torus shaped and spinning like a wheel in it's orbit around the sun). Or if the planet was pierced by something else that managed to not totally destroy it.

As I said, I cannot think of a natural process that would end in that arrangement. So, any unnatural process you like is fine.

I would note, though, that if I have the image in my head right - a wheel, one "face" of which faces the star at all times, spinning as if it were rolling along the path of its orbit - you aren't gaining much from that spin, unless it is wicked-darn fast. And at that point you've got issues keeping an atmosphere....

But then, we invoked magic to create the thing, so I'm probably being too nitpicky about the atmosphere.

Say, there is a continent on the Dark Side, basically isolated from the Light Side (especially seeing as winds would make it a little more difficult to do some migratory flying like birds do here).

Well, if the flying creatures can go very high, migrating might be easy - low-altitude winds help carry you sunward, high-altitude winds carrying them darkward.

 

[tylerthehobo]

There was a kind of fun mini-series on Fox (in the states) years ago about a tidally locked planet with a ('good') Victorian style society on the light side, and a ('nefarious') Medieval society on the dark side. A few noteworthy actors were even in it, but I guess since it bombed it never turned up on DVD:

White Dwarf (1995) (TV)

 

[AbdulAlhazred]

The process of becoming tidally locked will generally force the axis of rotation to be perpendicular to the plane of the orbit. You can have some small wobble, but nothing like the 23.5 degrees Earth has.

True in general. What about a world with a fairly good sized satellite? Maybe one in a fairly tight orbit. That would tend to allow for a greater tilt. It could also create a bit of darkness on the light side. Imagine it was large enough and close enough to eclipse the sun on each orbit. The dark would be pretty brief but it could have some fun implications.

There would also certainly be some degree of libration. If the orbit is a bit eccentric the terminator could move a substantial distance over the course of a year. That could be fun too.

So an area near the terminator could go from having a low sun angle to having the sun a bit below the horizon over the course of the year. All of these factors could combine to create some degree of variation in weather as well. It would almost certainly be less unstable than our weather is but in any case even unchanging conditions don't necessarily imply perfectly consistent weather all the time, just some sort of fairly steady state.

I doubt much would live on the dark side outside of some areas like deep sea vents, maybe hotsprings, or some area that received a fairly steady supply of nutrients from the light side. Any land area would most likely resemble the interior of Antarctica. With little in the way of flowing water on the surface the dark side would also probably be a rugged landscape. Mountains would erode very slowly. Without soil or much temperature variation to promote weathering the terrain would be somewhat different from what we're used to.

I could definitely imagine some creatures migrating out a ways onto the dark side to reproduce in an area where there would be few predators. It is hard to imagine any (mundane) larger organisms really making a living there on a full time basis though. Again think of Antarctica, but remember it is only in darkness half the year, yet there are virtually no higher land organisms at all. Penguins may haul out there and nest on the edges but they have an ocean to feed them too. Beyond that there are a couple other bird and seal species and a small number of arthropods (the largest land animal in Antarctica being 6mm).

Of course that's just the mundane backdrop...

 

[LightPhoenix]

Plant-wise: most plants sun-side are probably going to be photosynthetic in some way. Not necessarily green, but definitely converting solar energy to biochemical energy. On the other hand, dark-side "plants" will almost certainly be chemosynthetic - converting chemicals in the ground to biochemical energy. My guess though would be that the dark side is fairly lifeless when it comes to flora. You might get some phytoplankton-like bacteria, maybe some moss. Nothing large though - chemosynthesis can't provide enough energy at ground level to support complex life. If there were open lakes, chemosynthesis might be enough. At temperatures that constantly cold I think they'd be frozen too deep for anything on the surface to get at.

Animal-wise, on the sun-side pretty much anything goes. You could certainly have animals migrate out to the dark-side from time to time, but without food none would be permanent. You might have some scavengers that survive off of animals that get too far away from the sun-side.