Gliese 581g - A Tidally Locked DnD World

[UngainlyTitan]

Y'knw, I betcha that if one were a lich who wanted to be left alone do to one's studies, a great place to build a fortress would be the dark pole of the planet.

THe Fortress of Solitude

 

[Lanefan]

Another thought leaps to mind:

What if most of the life wasn't on the surface of this planet at all? I'm thinking "Hollow World" style, where most civilization is on an inside surface with only occasional quasi-legendary expeditions to the very-hard-to-reach outside.

Can you imagine the arguments over legend and religion? "The outside is dark and colder than bone!" "The outside is bathed in endless warmth and light!" "The outside doesn't exist, it's all a lie!" The first two would both be right, of course; depending on where that legend's original expedition happened to reach surface.

And the campaign, natch, could be simply a long and protracted surface expedition...

Lanefan

 

[El Mahdi]

The planet doesn't necessarily have to be all "land". If it has enough water to have oceans, the ocean currents would also contribute to moving heat around the planet (just like air currents). The Atlantic Gulf Stream is a good example. You'd still have a very cold and icy darkside, but perhaps not the binary desert/snowball scenario. It could possibly add a warming effect to the dark side, and a cooling effect to the light side. Sea creatures could spawn on the warmer light side, and live/hunt on the cooler dark side.

Playing around with the shape and dispersal of your continents and oceans (setting up varied ocean currents) could set up all sorts of interesting ecologies for the campaign world.

Along with adding volcanic activity, and the effect of different kinds of moons and orbits, you could still have a good amount of variety in climates and ecologies.

 

[Desdichado]

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

Actually, I'd think the center of the lightside hemisphere would be the genesis of some pretty severe planet wide weather systems. All that constant heating of the atmosphere will cause it to rise and cooler air will rush in to replace it, creating strong, sustained winds. In general, I'd expect this to be a world plagued by very strong prevailing winds, unusual storm activity and severe weather in general.

 

[Lanefan]

Actually, I'd think the center of the lightside hemisphere would be the genesis of some pretty severe planet wide weather systems. All that constant heating of the atmosphere will cause it to rise and cooler air will rush in to replace it, creating strong, sustained winds. In general, I'd expect this to be a world plagued by very strong prevailing winds, unusual storm activity and severe weather in general.

Yes, but those planet-wide weather systems, no matter how severe, would eventually reach a near-steady state and essentially never move after that.

The planet is not rotating, and coriolis force from Earth's rotation is a large part of what causes weather systems to move.

Yes, energy would be transferred by weather. Evaporation would always occur *here*, an endless wind would transfer the moisture over *there* to where it never stops raining, rain would fall, and the water would flow back to the sea. The main difference with Earth would be that the highs, lows, and fronts are permanent.

Lanefan

 

[Nifft]

Yes, but those planet-wide weather systems, no matter how severe, would eventually reach a near-steady state and essentially never move after that.

The planet is not rotating, and coriolis force from Earth's rotation is a large part of what causes weather systems to move.

Yes, energy would be transferred by weather. Evaporation would always occur *here*, an endless wind would transfer the moisture over *there* to where it never stops raining, rain would fall, and the water would flow back to the sea. The main difference with Earth would be that the highs, lows, and fronts are permanent.

Mmm. I'm not so sure. Cloud albedo might be sufficient to generate unpredictable weather, or at least weather patterns.

So far the proposed weather model has cold air being drawn from the dark-side to replace rising air heated by the sun on the light-side. This means we have a planet-wide layer of warm, moist air over a layer of cold, dry air -- moving in the opposite direction. That's a recipe for nasty weather, and the trigger for precipitation is going to be the turbulence between the atmospheric layers.

- - -

An interesting thought about this world's weather patterns, if they work as described above: we've got a fairly reliable pair of winds acting in opposite directions. Normally airships are limited to following whatever wind prevails, but with two well-known opposing forces, it would be possible to design some fairly reliable low-tech airships. Sea travel might not be convenient (i.e. it might suck that you would ALWAYS be tacking on your way Darkward), so perhaps airships handle the Sunward / Darkward axis, while sailing ships tend to travel between ports that are Equisolar.

Cheers, -- N

 

[Olgar Shiverstone]

Mmm.
So far the proposed weather model has cold air being drawn from the dark-side to replace rising air heated by the sun on the light-side. This means we have a planet-wide layer of warm, moist air over a layer of cold, dry air -- moving in the opposite direction. That's a recipe for nasty weather, and the trigger for precipitation is going to be the turbulence between the atmospheric layers.

IIRC, one of Larry Niven's Known Space worlds -- We Made It -- was a tidally locked world where the human colonists crash-landed in the habitable zone. All was well until the winds started. It resulted in some interesting ecology, with most of the life going subterranean, but with some explicitly adapting to above ground life under high winds. Some of the life forms adapted to having different ways to resist the wind; others adapted to using the wind to hunt and/or enable reproduction.

It would definitely make a great D&D setting.

 

[alms66]

Someone already mentioned that the winds would be constant in the twilight zone, however, I didn't see mentioned that the effect of that constant convection current in the twilight zone would be to turn it into a Sahara-like gigantic desert. This is the effect that occurs over Africa that causes the actual Sahara. Winds rise at the equator, flow north and cool, then drop down in North Africa and flow back south, drying the region.
So, I don't imagine the twilight zone being too inhabitable (only marginally so, like the Sahara). The same goes for the light side, 160° is going to create intense heating at the "pole" of the light side, causing giant convection currents there as well, and much drying over the region. But at the same time, it's going to fuel intense evaporation, so assuming there is a large ocean on that side as well, maybe the effects would balance out, or the high humidity would cause the light side to be covered in cloud constantly, making it perfectly habitable. Sort of like a "rain forest planet" on that side - warm, but not unbearably so.

That's my 2 cents to the story.

Edit:

An interesting thought about this world's weather patterns, if they work as described above: we've got a fairly reliable pair of winds acting in opposite directions. Normally airships are limited to following whatever wind prevails, but with two well-known opposing forces, it would be possible to design some fairly reliable low-tech airships. Sea travel might not be convenient (i.e. it might suck that you would ALWAYS be tacking on your way Darkward), so perhaps airships handle the Sunward / Darkward axis, while sailing ships tend to travel between ports that are Equisolar.

I'd imagine if air ships were developed, that they'd only go in one direction as well, and sea ships in the opposite. So then, you'd want to have an air ship that could convert to a sea ship when it was necessary to go in the opposite direction.

 

[Nifft]

I'd imagine if air ships were developed, that they'd only go in one direction as well, and sea ships in the opposite. So then, you'd want to have an air ship that could convert to a sea ship when it was necessary to go in the opposite direction.

Airships could go in either direction (Sunward or Nightward) by changing altitude, or they could do something they can't do in our world: move perpendicular to the winds, using one atmospheric layer as the "keel" layer and the other as the "sail" layer.

Airships would be more flexible transportation than sailing ships on this world, and that's pretty much the opposite of our world.

Hmm. Well, I guess one could make a combination airship / sailing ship which put all its sails on a dirigible (moored to the ship), and then sent the dirigible to the higher atmospheric layer for the trip Nightward. That might allow one to sail the Sunward/Nightward axis reliably.

Cheers, -- N

 

[tomBitonti]

Some stream of thought ...

What would happen if there was a large (pacific) type ocean that straddled the night/day terminator? There would seem a large convection cell with surface water travelling towards the dark / cold side and deep water flowing towards the light/warm side. At the surface, the winds are contrary to the water, and there would be a large energy transfer and moisture transfer from the water to the air. Would you end up with one big convection cell, or several? If the ocean reached far into both the warm and cold areas, how big of a temperature differential would you get? Would coasts deep in the cold zone be like the coast of Antarctica, with large, frequently calving ice sheets? As far as life goes, where would that ocean best support life? Where would there be large plankton blooms? I imagine that the energy transfer from the ocean to the air would largely be in the form of water evaporation. That energy would have to be released somewhere for there to be a complete energy cycle. Where would the energy be release? Would it be mostly as precipitation as the air mass moved towards and into the cold area? There should be predictable (but perhaps not steady) rains and snows near and past the terminator. Towards the sun-ward pole and anti-pole, would there not be the strongest winds, as the vast air masses crowded together to transfer between the upper and lower streams?

Thx!