Hmm. So, how possible is it for there to be life on a tidally locked world? Like, if it was orbiting a red dwarf or something, and was close enough to be tidally locked but still only got as much light as earth, would it be possible for there to be life? Maybe a thin habitable ring around the edge of the sunlit area? or would it just not be possible to have a viable atmosphere? :/
@Austin_Dern Hmm, gotcha. What about something a little crazier? With permanent glaciers and deserts, and constant rivers traveling from the dark side to the light?
(Also, what do you wall the various places? dark side, light side...? I keep wanting to call the ring the equator, but I know thats not right. :/
@Angle I don't know, but apparently there's numerical support for a livable spot on the sunlit side: https://arstechnica.com/science/2013/12/full-atmosphere-ocean-model-of-a-rotationally-locked-exoplanet/
Casual searching makes me think we're discovering lots of configurations aren't actually impossible. Not sure how many of them will be knocked out later, but there's grounds for play right now.
The ring separating the light and dark halves of a planet is the 'terminator'. I'd expect the prime meridian to be the terminator's average position over a full orbit.
@Angle (Without doing the work, I would *think* the exact terminator line would move slightly as the planet follows its elliptical orbit. That's a hunch though and shouldn't be confused with actual analysis. But it offers ecological niche potential, if it happens.)
@Austin_Dern Oooh, thats really cool. I had not considered that, I like it. It allows for something resembling seasons. XD
@Angle venus is very close to being tidally locked (nights that are something like 3/4rds of its year long) and iirc its 'dark side' is still atrociously hot b/c the extremely thick atmosphere conveys the heat around. i don't know if that would work with an atmosphere thin enough to have human-habitable temperatures, though.
@Angle Sounds like you have a better grasp of this sort of thing than I do, but wouldn't the weather be kind of horrific?
@shadowfirebird Maybe? I don't actually have much idea what this would look like, I just find the idea interesting. XD
@Angle @shadowfirebird I mean: one side always hot, one side cold -> a f***ing enormous pressure system.
@shadowfirebird yeah, but I think you'd pretty quickly have the hot side get mostly dehydrated, which limits the potential for pressure to build up? So you'd mostly just have a constant breeze. Though some places might see some horrendous wind. and I guess if you continue to have an atmosphere, there must be enough movement back and forth to allow for a healthy pressure system. :/
@Angle @shadowfirebird
My limited understanding is that in weather systems, hot air always moves to cold air. Something something constant rotational hurricane?
Depends on the temperature difference between dark and light sides, I guess. How close to the star are you? Is there something that could heat the arse-side of the planet?
@shadowfirebird Hmm, true. I figured the cold side of the planet would mostly just absorb all that thermal energy and have the air go right back. I guess you could end up with a hurricane? I was under the impression that you need a lot of water for a hurricane, though, and I figured most of the water would be locked up in the ice side of the planet. :/
@Angle Well, whatever you want to call a crapton of air rotating very fast because it's trying to equalise the temp / pressure diff. Not sure liquids are involved, it's just convection.
@shadowfirebird Mmm, but would it rotate? I guess it might. I was thinking it's just go to the dark side and freeze there. I guess it makes sense to have powerful rotating winds, though. Might even be another force keeping the atmosphere going... :P
@Angle Have you seen Stack Exchange's "World Builders" forum? some seriously physics folk there. Waaay smarter than I am.
https://stackexchange.com/search?q=tidally%20locked%20planet
@shadowfirebird Huh, no I hadn't I'll check it out. XD
@Angle Although, too much physics can kill a story. One of my favourite Zelazny novellas is set on an earth where constantly rotating winds have ripped the tops off the mountains. This makes no sense, but screw it, it's great.
@Angle
I also remember reading that if temp diff is bad enough, you don't get to keep the atmosphere at all. But I don't remember why -- just boils off into space? SF nut, not a physicist, sorry.
@shadowfirebird Mmm, I was worrying about it just condensing on the night side and staying there, so you just had big icebergs of frozen oxygen and nitrogen. Maybe there would be Glacial flows heavy enough to prevent this? Not sure how fast this would happen, nor what kind of force would be needed to balance it out. :/
@Angle I believe that another idea that has been suggested is that atmospheric and oceanic convection would even out differences of temperature to some extent.
@Angle My understanding is if the planet's got a short enough day/year, the atmosphere can rotate enough to leave moderate temperatures worldwide. But that requires a dim star so the planet can support a short day/year.
Given extremophiles I'm not sure very moderate temperatures are needed.