I don't think the "clear the orbit" criterion refers to a moon or double planet situation. It just means there isn't another big thing orbiting the star at the same distance. I don't know what shiggles and whatshingles are.

The moon is tidally locked to the Earth. The Earth is not tidally locked to the moon. If it was, the moon would only ever be on one side of the earth.

There is actually a science fiction book about just such a pair. One is a water world and the other dry. The human explorers arrive just as the water is about to switch planets in a once a millennium event. Fun read. I think it was Rocheworld? I think I only read the second one of the series.

There is also an animated movie featuring this concept voiced by kirsten Dunst called Kaena: the Prophecy. And the movie Upside Down, also starring Kirsten Dunst, that has some ideas on the socio-economic repercussions of such a setup.

Ultimately the math probably doesn't work out for any of these concepts without some fantasy style materials being involved. In order for two planets to be close enough to share an atmosphere would require orbits of such extremes that it would rip the planets apart.

I think it's possible. Robert L. Forward was a physicist and wrote a novel called Rocheworld which depicted such a world.

They are different sizes but Pluto and Charon are mutually tidally locked. They rotate around each other instead of Charon orbiting Pluto. They're really close together so they even share atmospheric gases every six days.

I don't get it. How exactly does the inverse square law tie into this specific case?

[removed]

I mean planets can definitely be tidally locked to a star, that's probably what you were thinking of. We have one (or two?) Of those in our solar system

Huh maybe, gota stop commenting without my glasses. Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. I'm probably wrong as idk wtf I thought tidal lock ment.

Based on this post, I believe you are smarter than you think you are.

What's the lower (upper?) bound on "similar size"? The Moon is pretty big, as moons go: is there something about similar masses that would prevent them from simultaneously tidally locking?

Even if they were in a perfectly perpendicular orbit around each other compared to their orbit around the star?

Not likely locked just slow rotation (check out "Eve Times Four" by Poul Anderson)

It wouldn't be that simple. You have to take the the inverse square law Into consideration

I think those are two distinct groups and neither are the majority they think they are.

And I assume this is due to earth's size/mass and 2 such bodies would compromise each other's orbit, whereas Pluto & Charon do their thing fine (not "planets").

I do wonder how interconnected to the planet we actually are, and won't really realise until people live off-Earth for long periods (i.e. years, maybe even decades).

Think of all the bacteria and tiny organisms we interact with on a daily basis. Like those in our soil, which end up in our food, which are crucial for plants to grow, the same plants that are proven to bring us well-being benefits.

Can we really live in a place that is essentially cut off from all the biodiversity that we evolved alongside? Sure, we can take soil and plants, and create little sanctuaries of Earth-nature, but it surely will always be nothing compared to a fully fledged ecosystem, let alone an entire planet.

[removed]

[removed]

AI robots are the solution imo. Even then an enormous amount of human resources would be needed for such a herculean effort.

If you mean like the Earth and Moon pair, that could work. If you mean two planets in the same orbit, that would be unstable.

Ive never overly liked or disliked him. But Ive always realized hes a danger to our society.

Yeah. It's basically science fiction and not worth worrying about that much. What we should be worrying about is all the problems we have put ourselves in on Earth. Climate change. Species die off. Habitat loss. Plastic and forever chemicals. Etc... Things that threaten our well-being right now.

[removed]

[removed]