Twin Planet Scenario

[Mouse]

Is there still a bulge on the face that is tidally locked, or is it just the same as everywhere else on the planet?

I'm thinking of the atmosphere as a very thin ocean. Maybe that's the wrong approach.

[Azélor]

Is there still a bulge on the face that is tidally locked, or is it just the same as everywhere else on the planet?

I'm thinking of the atmosphere as a very thin ocean. Maybe that's the wrong approach.

An ocean of liquid oxygen ? It become liquid at a very low temperature.
Would you like to drink some oxygen?

[Mouse]

Ummm.... Sorry Azelor. I meant that I thought of the movements of the atmosphere as being similar to the movements of a body of water.

I was imagining that if the water level would rise on Ethran in response to the presence of Errispa, then so would the atmosphere. Would that be right?

[rdanhenry]

You would see "tides" in the atmosphere, but on Earth solar heating effects dwarf those from gravitation. Figuring out if this changes for your twin planets with take some math and actual numbers for planetary data.

I am not buying that a double planet where they are of new-equal size has only one tidally-locked to the other. I'd think that they'd both be rotating freely or both locked. If I actually encountered such a pair, finding the asymmetry that allowed the situation would be at the top of my research list.

Judging from the map, Ethran is regularly eclipsed by Errispa: that would make the Errispa-side of the planet the colder half, as it's neighbor steals its sunlight. One would expect any massing of ice to appear there, rather than the reverse.

[Mouse]

You would see "tides" in the atmosphere, but on Earth solar heating effects dwarf those from gravitation. Figuring out if this changes for your twin planets with take some math and actual numbers for planetary data.

I was thinking more in line of an actual fluctuating 'lump' (not a big one, but enough to make a difference in the climate - higher pressure when its caused by sheer mass of atmosphere rather than being cooled by massive bodies of ice, meaning higher surface temperatures... yes/no?) in the atmosphere at the point where the planets are closest.

I am not buying that a double planet where they are of new-equal size has only one tidally-locked to the other. I'd think that they'd both be rotating freely or both locked. If I actually encountered such a pair, finding the asymmetry that allowed the situation would be at the top of my research list.

Ok, I can see that, but what if one of these planets is a rogue - a planet that came into the solar system spinning really fast. Over time, yes, they would become tidally locked to each other, especially at such a close range, but in the first half a million years? Would Errispa (the rogue planet) slow down and become tidally locked with Ethran straight away, or would it take a lot longer than that? (I have decided that the native planet was always spinning at about 1.5 Earth days per revolution to fit with Azelor's estimations - so that it becomes tidally locked almost straight away the moment the twinning happens)

Judging from the map, Ethran is regularly eclipsed by Errispa: that would make the Errispa-side of the planet the colder half, as it's neighbor steals its sunlight. One would expect any massing of ice to appear there, rather than the reverse.

That's what I first thought, but then I went through a convoluted thought process something like this (which you may find quite laughable, but its what I thought):

The distortion to Ethran caused by Errispa's gravity heats the planet, even more on the side facing Errispa. There is also increased thickness of atmosphere there - again owing to Errispa's gravity, which would hold more of the heat generated by the volcanic activity. The water would be warmer - as a result of the volcanic activity present close to the surface over the entire area, and the resistance of the thicker atmosphere to heat loss. Volcanic gases are mostly greenhouse gases - again reducing the heat loss and keeping it in that area. Its kind of a supergigantic supervolcano environment, around the edge of which there is a narrow habitable band - the ring of life. Go too far into the volcanic area and you can't survive, but go too far away from it and you freeze.

Why freeze? Well, the way I saw it in the eye of my mind was that if the planets were orbiting at the rate of one revolution per 1.5 days, and as close as they are to one another (which I have decided should be about 80,000 miles) one or both atmospheres will be eroding into space, and where on Ethran a large part of the atmosphere is concentrated over the face closest to Errispa, the rest of Ethran's atmosphere will be comparatively thin. Thin atmospheres cannot hold heat. The planetary thermal blanket is gone from all but the face closest to Errispa, so the oceans freeze.... or would they evaporate first and then the surface become like Mars?

Like I said - it's probably laughable, but its the way my imagination worked it out without any maths or physics and only rudimentary understanding of the thermal blanket nature of the Earth's atmosphere.

Does it make the slightest bit of sense to you?

[waldronate]

Physics has a tendency to break down in the face of God-like tech. For example, an interloper planet is pretty much impossible to capture by a similar-mass planet. They would fling each other out of the system in opposite directions. Something had to slow down that interloper dramatically and get it into a fairly stable orbit. Similarly, getting one of the planets to lock to the other would almost certainly cause them both to lock to each other because those forces go both ways without significant intervention.

The fun thing about storytelling is that an engaging story allows for a whole host of not-quite-right things to be ignored. As long as the characters act like believe it or if it's a mysterious element that the character are trying to resolve, the reader is likely to come along for the ride. If your story revolves around the concept of a giant eyeball moon that appears in the sky on a daily basis and the notion that the eyeball has a watching consciousness, then that will be a believable thing if your characters act appropriately.

[Mouse]

Almost as good as a flat earth theory isn't it

An interesting point. Physics versus story.

I think I was doing that in my head already, but it wasn't crystallised into words like that. I've been aware since I first had this idea (the result of a dream), that I would have to bend and possibly break the laws of physics, so in the plotline there is already a mysterious race of ancient aliens/original pre-apocalypse inhabitants of Ethran who actually 'called' Errispa out of the void by hitting it with bursts of laser fire while it was still over a light year away, and manipulating it onto exactly the right trajectory to come and join the solar system to allow for the expansion of their own civilisation - a second homeworld orbiting the star on the opposite side to Ethran.

It went wrong, and a group of heroes (prequel) managed to adjust the situation so that the twinning occurred, instead of an outright collision. The twinning itself was an apocalyptic event that (perhaps rather conveniently) wiped out the ancients and left a single indestructible AI device with a primary directive to recreate life on its destroyed planet - an intelligent 'genesis pod', which to the rapidly re-evolved humans would seem to be a God of sorts.

So... it really is all down to how well I weave my words.

Do I think I can persuade the reader?

Ummmmmmmmmm............

[Azélor]

I have no idea if the planets are really tide locked, I just made this under the assumption they were locked.

[Diamond]

Do I think I can persuade the reader?

Well, that's really what it comes down to, isn't it? I mean, both Tolkein's and GRRM's worlds make little to no sense on MANY fronts - geographic, economic, militarily, the list goes on. But readers seem to like 'em.

[rdanhenry]

Ok, I can see that, but what if one of these planets is a rogue - a planet that came into the solar system spinning really fast. Over time, yes, they would become tidally locked to each other, especially at such a close range, but in the first half a million years? Would Errispa (the rogue planet) slow down and become tidally locked with Ethran straight away, or would it take a lot longer than that? (I have decided that the native planet was always spinning at about 1.5 Earth days per revolution to fit with Azelor's estimations - so that it becomes tidally locked almost straight away the moment the twinning happens)

I'd say at this point you are writing space fantasy rather than science fiction and considerations of physics are no more sensible to apply than they are to Star Wars. That's fine, as long as you don't pretend it's scientifically plausible.

The distortion to Ethran caused by Errispa's gravity heats the planet, even more on the side facing Errispa.

Well, let's assume that the side that happens to be facing Errispa started off with a thinner and more fractured crust. Then you might well get the result that most of the triggered volcanism and seismic activity was on that side, bringing more heat to the surface.

There is also increased thickness of atmosphere there - again owing to Errispa's gravity, which would hold more of the heat generated by the volcanic activity.

Bear in mind that gravitational tidal effects will produce a similar thickness on the far side, assuming the analogy to oceanic tides hold, as I think it would. And that side still gets more sun. So, maybe you have a cold belt with two warm spots?

The water would be warmer - as a result of the volcanic activity present close to the surface over the entire area, and the resistance of the thicker atmosphere to heat loss. Volcanic gases are mostly greenhouse gases - again reducing the heat loss and keeping it in that area. Its kind of a supergigantic supervolcano environment, around the edge of which there is a narrow habitable band - the ring of life. Go too far into the volcanic area and you can't survive, but go too far away from it and you freeze.

Volcanoes also put up dust and ash which cool the planet. Whether volcanic activity serves to warm or cool on the whole depends on multiple factors, but you're fine stipulating that in this case it serves to warm things. However, all the warm air is high pressure. It will naturally move to the cold, low-pressure areas. Per your hypothesis, it will then be swept into space. This planet will not be habitable for long. You can recycle air on a tidally-locked planet if it freezes out on the dark side, air-ice glaciers push into the light, melt, evaporate, and renew the atmosphere, but you cannot get it nearly cold enough to do that with this set up.

Why freeze? Well, the way I saw it in the eye of my mind was that if the planets were orbiting at the rate of one revolution per 1.5 days, and as close as they are to one another (which I have decided should be about 80,000 miles) one or both atmospheres will be eroding into space, and where on Ethran a large part of the atmosphere is concentrated over the face closest to Errispa, the rest of Ethran's atmosphere will be comparatively thin. Thin atmospheres cannot hold heat. The planetary thermal blanket is gone from all but the face closest to Errispa, so the oceans freeze.... or would they evaporate first and then the surface become like Mars?

The ice will lose mass pretty rapidly. Earth without atmosphere would be at about 0 Fahrenheit. You're postulating a vacuum over the ice. It's going to sublimate rapidly. Details again depend on specifics, but I'm pretty sure the loss of any ice is going to go a lot faster than the tidal locking (and a lot of liquid water is going to go along with the atmosphere in the first place, before what is left gets frozen).

I think you're better off just ignoring the physics and accepting that you're writing a space fantasy. Attempting to justify it will just call attention to the implausibilities. Keep the story moving, accept the background as given, and most readers will go along with it. Better to leave things unexplained than try to prop things up with a bogus explanation.