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GODZILLA: KING OF THE MONSTERS - I have always believed Rodan is incapable of traveling into space because his strength is rooted in the Earth's magnetic field - which is what allows him to move with such incredible speed. :)

1. 3 of those monsters are space monsters. That means they can survive in space.

2. Mogera is a robot

3. Mothra, as guardian of the Earth with a life cycle resembling that of a phoenix, is very close to being a deity. Therefore, to protect the earth, she can but doesn't often unless necessary. (of course, you have to take "suspension of disbelieve" into account)

4. At this point in the game, it would look weird for Rodan to fly into space. He's an earth monster. There is no point for him to be in space (except for Invasion of the Astro-Monster, but he didn't fly to planet X. He did fly on that planet, but that doesn't count. I think).

At least, that is what I think. I just don't see Rodan going into space. Unless he's dive bombing an enemy from orbit or something.

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A lot of these monsters have weird properties that excuse the whole "flying into space" thing, like being from space, being a god, etc.

In my own writing, at least, the giant monsters CAN fly into space if they wanted to, they just don't generally do so because it's usually not part of their natural behaviour.

Don't know how much credence this has but pretty sure in the dub of Ghidorah the three-headed Monster during the monster "conversation" Rodan implies he can just leave earth if Ghidorah destroys it.

Maybe it's because Rodan needs to take in oxygen like us as well? Considering he is an Earth-Bound kaiju

^He survived on Planet X though. While Toho released material on how Godzilla was able to survive, I don't think they touched on Rodan--Though it's likely the same explanation.

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Gman- Didn't Planet X have it's own atmosphere?

I don't remember if Planet X has some sort of low-oxygen atmosphere, but probably since it clearly has gravity. And Rodan would need it to take flight. I'll have to look in to that. But the scientific accuracy of that at the time was likely lost on the filmmakers.

However, this book explained that Showa Godzilla's lungs can retain enough oxygen to where he doesn't need an oxygenated atmosphere to survive--At least for an unspecified amount of time. That's how he survived on Planet X. Here's a rough translation:

"While the exact function of Godzilla's lungs remain a mystery to an extent, his lungs can withhold massive intakes of oxygen, allowing him to survive without the need of respiration."

So that's how he could sleep underwater. That makes sense now.

^The Showa Godzilla also has a form of gills though.

If He Could Survive So Long Without Oxygen, What About The Oxygen Destroyer, Well.. I Guess The Corroding Is A Bit Self Explanitory.

Wow Think About This Conversation And How Much Of Nerds We Are, I Love It.

Ah, since we were briefly on the topic, I finally found the page from Tomoyuki Tanaka's book about Godzilla's gills. (Though his covering for visual shortcomings borders George Lucas levels of pandering.)