Valles is right. The exact match is not likely. So one planet will always be the dominant (even if not by much.)
One thing. I'm just tossing this off quick so I haven't rechecked it. But don't our oceans on Earth in concert with the Moon dampen the tendency for tidal lock? In other words - the tidal forces on the oceans that the Moon and Sun both produce that make the oceans wobble back and forth on the Earth's surface have prevented the planet from tidally locking to either the Moon or the Sun? Later I'll have to dig this up, but I've got a copy of a book called "What if the Moon didn't Exist" which goes into several different world-building scenarios including the title one. A no-Luna Earth scenario. An Earth where the moon was bigger. Or nearer. An earth where the moon was smaller, or further away, or more than one moon.
In other words, even if you assume a near parity in size between the worlds, if they both have substantial oceans, wouldn't it be possible for neither to be totally tidal-locked with each other?
One last thing - a familiar image from an old anime. Iscandar and Gamilon, the twin worlds featured so prominently in Star Blazers/Yamato in it's first season all these years ago. There's all kinds of interesting parallels between your idea and a lot of fanfic speculation (mainly done by an old friend of mine Derek Wakefield) about what would have influenced the cultures on those two planets and whether Gamilons and Iscandarians were related. But I'll leave that for another time.
But the main point of me bringing it up is this - in most of the images of the twin worlds Iscandar and Gamilon, they seem to share a sort of wispy diaphanous connection between them. Almost like a faint bubble nebula around them both. With a definite "column" of lighter space painted between them. Almost as if the atmospheres of both planets were shared between them. Or could that be charged particles in their shared magnetic fields?
Here's a pic of what I mean (kinda hard to find, really, but my google-fu is good. ^_^)
![[Image: Desraa_Iscandaa.jpg]](http://www.starblazers.com/images/newsletter/august03/Desraa_Iscandaa.jpg)
If that's charged particles, then their shared night sky would be FANTASTIC. Though it would hamper astronomy somewhat.
I find the idea of a shared atmosphere though more compelling. Though somewhat less likely. There is precedent for a smaller than Earth-sized body to maintain a substantial atmosphere. Saturn's moon Titan has a thick methane atmosphere, though IIRC it's smaller than Mars. How is this possible? Gas Torus effect. Titan does in fact not have enough native gravity to maintain the atmosphere, but the atmosphere that leaks away is still caught in the same orbital track by Saturn and thus Titan is continuously orbiting through the gas torus of it's own atmosphere and picking it back up again.
Could something similar happen between two near-earth sized worlds? So that their atmospheres co-mingle maybe even to the point of shared biota?
(One borderline wacky idea I had many years ago that I still find compelling was that of Iscandarians exploring and colonizing Gamilon (and later evolving adaptations that made them Gamilons) not with rockets, but with JETS crossing the void and staying inside that column of air between their worlds. Yes, I know it's pretty preposterous. But I felt at the time that I was working within the sort of "rubber physics" displayed in the show itself. ^_^)
EDIT: Although... I'm thinking that unless all those pics of Gamilon/Iscandar are being shown at such an angle that one larger planet is significantly closer to the "camera" POV than the other, that there's a problem with the basic idea. If we are looking at the two worlds dead-on side by side, than aren't they TOO close to each other? Inside each other's respective Roche limits in other words? Or am I wrong?
Oh well - "rubber physics" like I said above. None of Matsumoto's works, including Yamato, were ever known for rigorously adhering to physics as we know it. ^_^;
One thing. I'm just tossing this off quick so I haven't rechecked it. But don't our oceans on Earth in concert with the Moon dampen the tendency for tidal lock? In other words - the tidal forces on the oceans that the Moon and Sun both produce that make the oceans wobble back and forth on the Earth's surface have prevented the planet from tidally locking to either the Moon or the Sun? Later I'll have to dig this up, but I've got a copy of a book called "What if the Moon didn't Exist" which goes into several different world-building scenarios including the title one. A no-Luna Earth scenario. An Earth where the moon was bigger. Or nearer. An earth where the moon was smaller, or further away, or more than one moon.
In other words, even if you assume a near parity in size between the worlds, if they both have substantial oceans, wouldn't it be possible for neither to be totally tidal-locked with each other?
One last thing - a familiar image from an old anime. Iscandar and Gamilon, the twin worlds featured so prominently in Star Blazers/Yamato in it's first season all these years ago. There's all kinds of interesting parallels between your idea and a lot of fanfic speculation (mainly done by an old friend of mine Derek Wakefield) about what would have influenced the cultures on those two planets and whether Gamilons and Iscandarians were related. But I'll leave that for another time.
But the main point of me bringing it up is this - in most of the images of the twin worlds Iscandar and Gamilon, they seem to share a sort of wispy diaphanous connection between them. Almost like a faint bubble nebula around them both. With a definite "column" of lighter space painted between them. Almost as if the atmospheres of both planets were shared between them. Or could that be charged particles in their shared magnetic fields?
Here's a pic of what I mean (kinda hard to find, really, but my google-fu is good. ^_^)
If that's charged particles, then their shared night sky would be FANTASTIC. Though it would hamper astronomy somewhat.
I find the idea of a shared atmosphere though more compelling. Though somewhat less likely. There is precedent for a smaller than Earth-sized body to maintain a substantial atmosphere. Saturn's moon Titan has a thick methane atmosphere, though IIRC it's smaller than Mars. How is this possible? Gas Torus effect. Titan does in fact not have enough native gravity to maintain the atmosphere, but the atmosphere that leaks away is still caught in the same orbital track by Saturn and thus Titan is continuously orbiting through the gas torus of it's own atmosphere and picking it back up again.
Could something similar happen between two near-earth sized worlds? So that their atmospheres co-mingle maybe even to the point of shared biota?
(One borderline wacky idea I had many years ago that I still find compelling was that of Iscandarians exploring and colonizing Gamilon (and later evolving adaptations that made them Gamilons) not with rockets, but with JETS crossing the void and staying inside that column of air between their worlds. Yes, I know it's pretty preposterous. But I felt at the time that I was working within the sort of "rubber physics" displayed in the show itself. ^_^)
EDIT: Although... I'm thinking that unless all those pics of Gamilon/Iscandar are being shown at such an angle that one larger planet is significantly closer to the "camera" POV than the other, that there's a problem with the basic idea. If we are looking at the two worlds dead-on side by side, than aren't they TOO close to each other? Inside each other's respective Roche limits in other words? Or am I wrong?
Oh well - "rubber physics" like I said above. None of Matsumoto's works, including Yamato, were ever known for rigorously adhering to physics as we know it. ^_^;