Gliese 581g - A Tidally Locked DnD World

[Xeviat]

There were articles showing that a small atmosphere will protect against "freezing out"; the atmosphere only needs to be 10% as thick as Earth's to prevent that.

Also, this planet rotates every 37 days; it is much slower than every 24 hours, but it still rotates. As long as the core is molten, it will have some dynamo effect. And as Umbran says, the star is less dangerous.

Another thought for a geological cycle would be the tides caused by the moon. Since I want solar and lunar eclipses, the moon is going to have to be bigger or closer. Too big or too close, though, seems like it would create a dual planet situation, rather than a planet and a moon, so I might have to go for partial eclipses (which would mean there is absolutely no darkness on the day-side). Either way, with a slow lunar rotation, the tides will move slower. A larger or closer moon will create more drastic tides, which will likely drive the lifecycles of aquatic life. Tidal shores will be big. If life started in these tidal shores, they could be the basis for a large food chain.

I'm not sure what I want to do about sleep cycles. Sleepless humanoids as the norm feels odd, and I wouldn't want any race to have such a widely different sleep cycle than the others as that would affect play.

Aside from the geology and astronomy of the world, I started putting some thought into the cultures of humanoids living here (as every gaming setting has some sort of multiple races). I think the night-siders, or at least those far enough into the twilight to see the stars, will be the more advanced, both religiously and technologically. They have the stars to watch, which leads me to believe they will have a deeper knowledge of mathematics. They will likely worship the omnipotent stars, and will most definitely have noticed the paths of the outer planets in their system. They will be able to keep time.

The day-siders seem like they'd be more primitive. I haven't given them too much thought yet, but I wanted to find a way to avoid the immediate thought of having the daysiders be good and the nightsiders be evil.

I also think that mountains in mid latitudes (pretending the terminator line is the equator, since it will be more apparent than the actual equator) will house the largest day-side cities in their shadows. The mountains will collect rain, and as long as the mountains are small enough, some of that rain water could flow to the shadow-side; especially if the people create canals to channel the water around the mountain.

I wasn't looking for the moon to create a "day and night" in a duration, just to give the day-siders something to keep time. I'm thinking to have the day-siders keep time by months, counting each time the moon rises.

 

[Wik]

After reading this thread, and realizing just how damned cool it is, I can't help but think of an elven culture that lives in the gigantic sun-side jungles and makes holy pilgrimages to the dark side to look at the stars to foretell their future. And these elves, after living their long lives in the sun side, would go to the dark side to die.

And then there are the drow elves, who have decided to pay all their attention to the stars and foresake the sun in preference for religious fanaticism. And since the other elves "don't listen to reason", these drow want to kill their light-skinned cousins.

The idea of giving the planet a ring, perhaps like Eberron's dragon shards or whatever they're called, is also pretty cool.

I also like the idea of a rogue planetoid that comes around every, say, thousand years or so, which essentially FLIPS the planet, so that the dark side effectively becomes the light side, and the light side goes dark. This, of course, would make for a great campaign - imagine if the planet was destined to flip next year?

 

[Darynal]

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!

I like your thinking! Almost didn't read this because it was one big paragraph, so I separated it for my own sake =)

This is a pretty cool thing to consider about a tidally-locked setting. It makes me think of Dark Sun's backdrop in terms of the unique kind of global phenomena that can be encountered.

 

[Merkuri]

I also like the idea of a rogue planetoid that comes around every, say, thousand years or so, which essentially FLIPS the planet, so that the dark side effectively becomes the light side, and the light side goes dark.

Is there something that would really do that? In the real world, is it possible for a tidally locked planet to flip without something massively destructive, like a meteor strike?

 

[Wik]

Is there something that would really do that? In the real world, is it possible for a tidally locked planet to flip without something massively destructive, like a meteor strike?

Probably not. I am totally not a science person.

That being said, uranus and pluto switch orbits, in part due to their proximity to one another at a certain point in their orbit around the sun.

 

[Camber]

Also, this planet rotates every 37 days; it is much slower than every 24 hours, but it still rotates. As long as the core is molten, it will have some dynamo effect. And as Umbran says, the star is less dangerous.

The "rotation" of 37 days only means that the planet rotates relative to a stationary observer, but not relative to the red dwarf. Theh same side always faces the red dwarf.

The National Geographic piece http://www.youtube.com/v/CNeTxPgGJ7I&hl noted that red dwarfs are almost always flare stars--they would be very dangerous neighbors if you didn't have some way of protecting yourself from being cooked by the solar flares (especially when you are as close to the star as Gliese 581g appears to be).

There's a nice page answering some questions on the planet here.
One of the sidebars showed a comparison of this planet's orbit with Earth's, and you'll note how close it is to some large planets. I wonder if there could be any tidal pulling from the nearby planets? They seem to be rather tightly packed together compared to the setup we have at Sol.

I've run into some information (here is an example) on magnetic fields, vulcanism, and rotation that suggest that rotation and magnetism of a planet are connected. For example, Venus used to be volcanic, but appears to have cooled down internally to the point that its molten core didn't flow in currents anymore, which caused it to lose its magnetism, which in turn caused it to virtually stop rotating. Mars similarly seems to have lost a lot of its internal temperature, which has caused its vulcanism to slow down, but it is still rotating pretty rapidly (almost as fast as Earth).

Here's an interesting quote on the topic (again, from here):

Mars: Its in-between geology suggests it is possibly too cool for molten core, or possibly just hot enough. Because of its relatively rapid rotation (almost as fast as the Earth's), a molten core should produce magnetic field, but only a minuscule field is observed, which implies that it may be too cool (probably less than 5000 Fahrenheit degrees) to have a molten core. However, fossil magnetism at the surface suggests that the rocks which contain that magnetic signature were formed at a time, 4+ billion years ago, when Mars had a substantial magnetic field; and parallel striping of that fossil magnetism in certain areas suggests that in that same time frame, something occurred similar to the seafloor spreading and magnetic striping caused by magnetic field reversals in the Earth. So although Mars' core must be relatively cool and solid now, it was undoubtedly hot enough to create an active magnetic field and drive some mantle activity, in the very early days of the planet's history.

It leads me to think of the magnetism of a planet as being kind of like its life-force. When the planet cools down and the magnetism is lost, the planet has essentially died, and eventually you lose rotation also. This would lead one to say that Gaia is still alive, Mars is limping along, and Venus is essentially dead.

So a tidally-locked planet that has vulcanism because of outside forces (such as tidal forces) instead of from internal magnetism and magma currents might be sort of undead--an animated but dead planet.

Back in 2e, my home world of Jera was much like this in the past.

The work of the legendary heroes Ironheart and Steelaxe made the world spin again.

The idea of having a story focused around efforts to restart the rotation of a planet is one that is full of interesting possibilities. What if the thing that was needed was to reheat the core and get it magnetized again, which would then slowly jump-start the rotation.

I am envisioning it taking a great deal of power and energy, probably at great cost. Just exactly what that cost would be, and how the decision is made to make the necessary sacrifices, is what would make the story interesting to me.

 

[El Mahdi]

...The idea of having a story focused around efforts to restart the rotation of a planet is one that is full of interesting possibilities. What if the thing that was needed was to reheat the core and get it magnetized again, which would then slowly jump-start the rotation.

I am envisioning it taking a great deal of power and energy, probably at great cost. Just exactly what that cost would be, and how the decision is made to make the necessary sacrifices, is what would make the story interesting to me.

A high-yield Cobalt_Thorium-G_Doomsday_Device buried very deep, should do the trick...

 

[Xeviat]

The "rotation" of 37 days only means that the planet rotates relative to a stationary observer, but not relative to the red dwarf. Theh same side always faces the red dwarf.

Just wanted to point out that movement is relative to stationary space. You may not feel that the earth is wizzing around the sun as fast as it is, but it is. You may not feel that it is spinning, but it is. 581g is rotating every 37 days; it's tidally locked, but there will still be a centrifugal effect.

For example (an example from a Physics book), if you spin a bucket full of water, you create a whirlpool in the bucket. If you suddenly stop the spinning, the water continues for some time; force has been imparted into it, and it takes it a bit longer to lose this. This spinning is in relation to space, not the objects around it. Otherwise, you would get the same spinning force if you spun the room around the bucket of water. I may be remembering the analogy incorrectly, but my point is that just because the planet isn't spinning in relation to the star doesn't mean it isn't spinning. Venus is nearly tide locked but it spins enough that its atmosphere super rotates.

I had an article that explored the coreolis effect on slowly rotating bodies; I cannot find it again since I do not know what google-fu lead me there, but it did show that even an object rotating every 365 days (a tidally locked Earth for example) would have centrifugal force suitable to create some sort of magnetic field.

As for the issue of flare stars, for a setting I'm going to assume that my world began to evolve after the star's flare stage was over, or that the star was more stable. Red Dwarfs live far longer than Yellows, so the world has plenty more time to evolve.

 

[Camber]

Ah, I think I understand you now. So you aren't saying, for example, that the rotation would be such that it would cause the terminator line to move if a settlement were built on it (you could expect the terminator line to be fairly stable), but you are saying that the rotation that is present (once every 37 days) would be quite a bit and enough to possibly rev up some magnetism and volcanic activity?

I was doing some research on the relationship between magnetic fields and rotation, and it is amazing how little we know about it other than that there is a strong connection, and that it doesn't always hold true. Dynamo Theory is widely accepted as the best current explanation for the connection, but it doesn't adequately explain all of the energy produced in the core of a planet like the Earth (current mathematical models suggest that the magnetic effect would die down in 20,000 years--there is a great deal of sustaining energy that we can't account for). There's a very interesting non-mainstream theory called the Georeactor Dynamo Theory that suggests that uranium sinks to the planetary core, where it is concentrated enough that a low-level fission reaction is created. In gas giants such as Jupiter, which produces far more energy than it takes in from the sun, a low-level fusion reactor is proposed, in which hydrogren is fused under pressure but at cooler levels than those needed to turn it into a star.

As has been said, red dwarfs are extremely long-lived, and it is likely that Gliese 581g planet could be on the latter end of the star's lifespan, perhaps a few billion years after the uranium or whatever else is helping to keep the dynamo going has been burnt out. Or, in more supernatural terms, after the planet's spirit has died out.

Why is it that celestial bodies tend toward being tidally locked over time? Is there any reason other than gradual loss of energy, and is it inevitable that all planets will eventually be tidally locked with their star(s)?

 

[Xeviat]

Ah, I think I understand you now. So you aren't saying, for example, that the rotation would be such that it would cause the terminator line to move if a settlement were built on it (you could expect the terminator line to be fairly stable), but you are saying that the rotation that is present (once every 37 days) would be quite a bit and enough to possibly rev up some magnetism and volcanic activity?

Well that sucks; I had a whole post done last night and it didn't go through. I'll try to remember what I typed.

Yes, a 37 day rotation should be fast enough to get a liquid core spinning a bit. I don't know if being tidally locked will tide lock the core as well, though. I suspect not; Mercury is tidally locked for a large portion of its orbit, and it still has a magnetic field (1% the strength of Earth's). Mercury is smaller and it rotates slower than 581g (Mercury rotates 3 times for every 2 orbits around the sun; it's tide locked when it is close and rotates halfway when it's far); it rotates once every 59 days, or 60% the speed of 581.

Since 581g is larger, it could have more iron in its core. The larger size combined with the faster rotation means the core is spinning faster (37 days for a planet larger than earth is much faster than 59 days for mercury). I would suspect that 581g, if its core is still molten (and it is larger so it should hold onto heat longer), should have some magnetic field. Plus, this is where fantasy could jump in and assist.

I also suspect a thicker atmosphere, combined with the lower UV output of the star, and the higher gravity, should help 581g hang onto more of its atmosphere (If I'm correct, the biggest problem is photons from the sun energizing air molecules so much that they escape the planet's gravity).

Why is it that celestial bodies tend toward being tidally locked over time? Is there any reason other than gradual loss of energy, and is it inevitable that all planets will eventually be tidally locked with their star(s)?

Wikipedia has a good article on this. The main issue is that a large body creates large tides on an orbiting body. That tidal bulge acts as an anchor, which the larger body is tugging on. This will slow the smaller body's rotation until that tidal bulge is directly between the two bodies. Like how the moon creates a tidal bulge in our seas, but since the moon is smaller it doesn't have enough gravity to use it as a break (I think it's actually causing the moon to move further away).

I was looking into some more indepth astronomy, and I hear there is a way to determine the optimal orbital distance for moons around a planet. Something about the gravity well it creates. Too close to the parent star, the planet's gravity well may be too shallow to hold a large moon. I'm just curious, as I'd like a moon or moons for appearance but I don't want them if I'm going to have to support them with magic.