Gliese 581g - A Tidally Locked DnD World

[Woas]

Wouldn't all the water be frozen on the dark side since it would be extremely cold, never receiving any solar energy? The water vapor would move across from the hot side to the cold, condense, and then eventually freeze generating a huge half-world sized glacier.

 

[Umbran]

Wouldn't all the water be frozen on the dark side since it would be extremely cold, never receiving any solar energy? The water vapor would move across from the hot side to the cold, condense, and then eventually freeze generating a huge half-world sized glacier.

That would be the tendency, yes. Nifft and I are invoking a few potential mechanics for getting some heat to the dark side - make dark and cool, not dark and frigid, to avoid that problem.

 

[Nifft]

I'm not sure exactly what you intend to say here, but if my first guess at your intent is correct, then your statement is incorrect.

"I don't know what you mean, but I know you are wrong."

There's not much reason to think a stable planet-moon pair can't be there. There's some restrictions on it (basically, some orbital resonances), but otherwise, it's quite feasible.

The effect of the moon can't violate phase lock, since that's our initial assumption, so the moon can't have much effect on the planet.

Gliese 581 is a red dwarf, smaller and cooler than our Sun - the sun as a surface temperature of about 5780 Kelvins (9900 F), while Gliese 581 is about 3480 Kelvin (5804 F). That means less violet and UV radiation than the Sun puts out - a lot less.

And, if there's that much UV in the atmosphere that enough gets scattered to make the night side habitable, the day side would be uninhabitable, as the exposure to intense direct UV would tend to break the bonds in complex molecules required for life.

Depends on the cloud cover of the day-side. We're not dealing with an entity of uniform composition. The cloud cover will vary drastically.

But if the star isn't going to emit the light in the first place, it's moot.

It would (imho) more plausible to simply hand wave and say that there's enough atmospheric mixing to spread heat around and leave the night side habitable.

Warm + lightless isn't habitable. Food won't grow. This is my major beef with the Underdark.

On the other hand, habitable does include places that are frosty but where there is enough ambient energy that food can grow. We can build shelters to catch ambient non-heat energy and turn it into heat, but turning heat into useful energy is somewhat more challenging.

Wouldn't all the water be frozen on the dark side since it would be extremely cold, never receiving any solar energy? The water vapor would move across from the hot side to the cold, condense, and then eventually freeze generating a huge half-world sized glacier.

Apparently some new models show that to be incorrect.

There are a bunch of links to specific debunkings of that -- and the theory that the atmosphere would boil off on the light size and freeze solid on the night side -- in the thread.

Cheers, -- N

 

[Umbran]

The effect of the moon can't violate phase lock, since that's our initial assumption, so the moon can't have much effect on the planet.

Define term, "much". Also note that what doesn't seem like much to the planet might be major for the living things upon it. A little bit of wobble may not make huge differences in temperatures at the Noon and Midnight poles. However, it might give you something akin to seasons in the twilight regions that might set lots of time-dependent behaviors in the life there.

Depends on the cloud cover of the day-side. We're not dealing with an entity of uniform composition. The cloud cover will vary drastically.

I don't think you're going to get enough UV scatter above the cloud layer to heat the dark side. Above the clouds the air is thin, and thus doesn't scatter much. Overall, the atmosphere isn't a fiber-optic cable.

Warm + lightless isn't habitable. Food won't grow. This is my major beef with the Underdark.

Photosynthesis is not the only way to go. Check out the deep sea near volcanic vents - no sunlight, but lots of life.

There are a bunch of links to specific debunkings of that -- and the theory that the atmosphere would boil off on the light size and freeze solid on the night side -- in the thread.

I only see one that references it, and it is more interested in whether the planet holds an atmosphere at all:

Aurelia and Blue Moon - Wikipedia, the free encyclopedia


"Nonetheless, the scientists employed by the programme decided to test the traditional assumptions for such a planet and start a model out for it from a proplyd through to its eventual death. Their estimations suggested such a planet could indeed hold on to its atmosphere, although with freakishly unusual results by Earth standards. Half of Aurelia would be in perpetual darkness and would be in a permanent ice age. The other half would contain a giant, unending hurricane with permanent torrential rain at the point directly opposite the local star. In between these two zones would be a place suitable for life."

Other links are about magnetic fields and fictional worlds. Which ones am I missing?

 

[Nifft]

Define term, "much". Also note that what doesn't seem like much to the planet might be major for the living things upon it. A little bit of wobble may not make huge differences in temperatures at the Noon and Midnight poles. However, it might give you something akin to seasons in the twilight regions that might set lots of time-dependent behaviors in the life there.

"Much" = enough to give significant tides, promote vulcanism, and keep the planetary dynamo working longer than it otherwise would have worked.

I don't think you're going to get enough UV scatter above the cloud layer to heat the dark side. Above the clouds the air is thin, and thus doesn't scatter much. Overall, the atmosphere isn't a fiber-optic cable.

It isn't a good fiber optics cable, but a nice thick atmosphere can carry light around the curve of a sphere, and ours does.

Their atmosphere could easily be thicker, what with their planet having a higher surface gravity.

Forget UV and just think about violet & blue light. There could be crops which will grow in a twilight zone which never sees their sun.

Photosynthesis is not the only way to go. Check out the deep sea near volcanic vents - no sunlight, but lots of life.

Yep, but that energy is not heat. It's chemical. The paragraph after the one you quoted hints at this same point:

On the other hand, habitable does include places that are frosty but where there is enough ambient energy that food can grow. We can build shelters to catch ambient non-heat energy and turn it into heat, but turning heat into useful energy is somewhat more challenging.

... but sure, I could have spelled that out more explicitly for you; and yes, deep sea vents on both sides of the planet would have plenty of non-photosynthetic life.

But: so what? How are those vents relevant to life on the surface of the night side?

I only see one that references it, and it is more interested in whether the planet holds an atmosphere at all (...) Other links are about magnetic fields and fictional worlds. Which ones am I missing?

Here's one from a link on page 3:

Researchers also know that the planet is tidally locked to its star. That means one side experiences eternal daylight, and the other side experiences unending darkness. Such a locked configuration helps to stabilize the planet's surface climate, Vogt said.

3-D global circulation models have shown that the temperature differences on the day and night sides of the planet would not be enough for water to either freeze or boil off. They also suggest that the atmospheric circulation and wind patterns would be relatively benign.

I've bolded the relevant passage.

It's in a post by Camber.

 

[Umbran]

"Much" = enough to give significant tides, promote vulcanism, and keep the planetary dynamo working longer than it otherwise would have worked.

Well, we don't as yet know if natural satellites large enough to do that are common, in general, much less whether they're likely in this particular sort of case. However, since you can get all that from a satellite that's in a resonant orbit, it is at least possible.

It isn't a good fiber optics cable, but a nice thick atmosphere can carry light around the curve of a sphere, and ours does.

Well, it is specifically a pretty crappy fiber-optic cable. Yes, some light does make it over the horizon, but not by much. I thought you were talking about having light reach great distances toward the dark pole, sufficient to drive heating and growth there, and that's unlikely.

Their atmosphere could easily be thicker, what with their planet having a higher surface gravity.

We know the mass of the planet, but so far, we don't have a good handle on its size - so, we don't know yet if the surface gravity is higher. It is probable to be higher, but not a surety, and not necessarily higher by much.

Yep, but that energy is not heat. It's chemical.

Doesn't matter - the point is that life can use a variety of energy sources.

There's no particular reason why life can't use a heat engine, if that's all that's available. So long as you have a temperature gradient, you can have a heat engine. You could imagine huge heat-engine beds of moss-like material blanketing the surface, using a gradient across hundreds or even thousands of miles... classic D&D brown mold!

Or, perhaps more simply, if there's significant atmospheric (and/or oceanic) mixing from one side to the other, the dark may get significant influx of complex organic material (or the equivalent, if they aren't carbon based). So, the dark side could then use chemosynthesis like an undersea vents ecology, or be essentially saprophytic like a cave ecology.

Or, since we are talking about a fantasy world, you can have a system based on arcanosynthesis - magic as the underlying energy!

Here's one from a link on page 3: I've bolded the relevant passage.

It's in a post by Camber.

Ah, got it. Sorry, I thought you were referring to links more specifically about those models.

 

[Xeviat]

I'm not so much concerned with specifically modeling 581g anymore, especially considering it is in the "unconfirmed" pile of planets again. I'm looking at a planet in a similar situation, more like Aurilia (though I don't want the night-side glacier to be so encompasing; I figure more ocean on the planet would lead to better heat transfer).

To get a moon that nearly eclipses a red dwarf in the sky of a tidally locked planet, the moon is going to need to appear larger than ours. This means it needs to be considerably closer, or considerably bigger. It could be bigger, as the planet can be bigger, but some have pointed out that large satelites appear to be rare from our own solar system's guidelines (our own moon is throught to have come from a massive colision). A similar situation could have occured.

Now, what I'm thinking could be interesting, but still simultaneously useful for time keeping and suitably different from Earth, would be if such a planet had a few moons. They would create more frequent eclipses of the sun, which would aid in the tracking of time. Additionally, at least closer ot the twilight, if the star has more planets further interior, these could be seen as stars moving in and out of the star, and they'd prove useful (but the twilight side will be able to see the actual stars, which will drift in the sky rather quickly).

I also think I will be using chemosynthesis as the primary source of food on the night side. Vast gyser fields and hot springs will support chemosynthetic bacteria and fungi that animals feed off of. Other life will be supported by organics brought in from the day side (the ocean should still get a good supply of plankton and such on the ever circulating ocean currents).

I'd prefer to keep the magical ecosystems to a minimum, but this is because of my preference towards worldbuilding with an eye to Sci Fi.

Thanks for everyone's help. This is a fun discussion.

 

[Nifft]

Ah, got it. Sorry, I thought you were referring to links more specifically about those models.

I posted content from one link which specifically and directly answers the question posted. What more did you want?

 

[Umbran]

I posted content from one link which specifically and directly answers the question posted. What more did you want?

You want a detailed answer? The issue isn't what I wanted, but what I was looking for and/or expecting.

You said, "There are a bunch of links to specific debunkings of that -- and the theory that the atmosphere would boil off on the light size and freeze solid on the night side -- in the thread."

When I looked, I didn't see that. I saw a bunch of links to general articles on the planet (and some on geomagnetism). Buried in one of the general articles was a short assertion of reaching a different result on the atmosphere.

I was expecting were several links that were specifically and primarily about the atmospheric modeling, with more details and discussion of what the new model found, and how it differed from the old model. For real debunking, I'd even expect to see evidence that the original result wasn't just inaccurate, but downright fakery with no science behind it at all. It isn't like Einstein "debunked" Newton, after all.

So, when I went looking, I didn't see what I call "a bunch", "specific", or "debunking". See my previous note about being my being (perhaps unfortunately) picky about terminology when talking science. Mea culpa.

 

[Nifft]

For real debunking, I'd even expect to see evidence that the original result wasn't just inaccurate, but downright fakery with no science behind it at all. It isn't like Einstein "debunked" Newton, after all.

It is inaccurate, and there is no science behind the "theory" that the atmosphere would both boil off and freeze out, or that all the water would be locked on the night side. It's just a bunch of simplistic reductionist intuition wrapped in science-y terms.

So, when I went looking, I didn't see what I call "a bunch", "specific", or "debunking". See my previous note about being my being (perhaps unfortunately) picky about terminology when talking science. Mea culpa.

You saw one, and I've pointed you towards another, both of which specifically refute the notion of phase-locked planets being uninhabitable.

I'd like to see their atmospheric models in more detail too, but they're both quite specific in that NOT all water in any of their models ended up locked on the night-side.

Be as picky as you want with science terms -- rigor is good for us -- but please try to apply that rigor to yourself as well, and honestly tell me that this isn't a specific refutation of the the claim made by Woas:

3-D global circulation models have shown that the temperature differences on the day and night sides of the planet would not be enough for water to either freeze or boil off.

This is the claim being debunked. Emphasis added:

Wouldn't all the water be frozen on the dark side since it would be extremely cold, never receiving any solar energy?

- - -

Okay, now that we've firmly established whatever the hell that was about, let's get back to talking about cool phase-locked worlds for games.

Perhaps it's possible to have a layered atmosphere, since the planet is so much larger than the Earth. There could be a "high" atmosphere comparable to our own, where human-ish life can develop, but over the seas and in deep canyons there is a layer of something heavy and greenhouse gassy, which may or may not be toxic to people, but should be uncomfortable. This layer could carry heat deep into the Nightside, and could reach land-bound glaciers without being in danger of freezing out itself.

So, in addition to the atmospheric cycles going on in the normal earth-like layer, you'd have these hot chasms which might never see sunlight, but are home to howling winds and severe weather, including "lake-effect" rainfall where prevailing winds run over these canyons.


I like this idea for a few reasons:

1/ A great excuse for Mars-like canals.

2/ A great excuse for airships to cross over the deep, hot oceans of inhospitable mist.

3/ A great excuse for piping heat over to the dark side.

Cheers, -- N