Beanstalk for a tide locked world?

[Flyndaran]

Originally Posted by jeff_wilson

The way you says this makes me wonder if you had some wider separation of the double planet in mind, something like millions of miles?

No. I just thought that two habitable sized planets would orbit much further out than if one were a much smaller moon.

[Agemegos]

Originally Posted by Flyndaran

No. I just thought that two habitable sized planets would orbit much further out than if one were a much smaller moon.

Well, I haven't done any calculations on the subject, but I would have thought the reverse. You have very roughly twice as much rotational energy to dissipate, but the gravitational attraction between two bodies of Earthlike mass is on the order of eighty times that between the Earth and the Moon, so it takes about eighty times as much energy to move them apart to the same separation.

I haven't even gone near the back of an envelope, but my rough estimate is that tidal effects would have drawn twin worlds apart 1/30 times as much as they have moved the Moon outwards.

[jeff_wilson]

Originally Posted by Brett

Well, I haven't done any calculations on the subject, but I would have thought the reverse. You have very roughly twice as much rotational energy to dissipate, but the gravitational attraction between two bodies of Earthlike mass is on the order of eighty times that between the Earth and the Moon, so it takes about eighty times as much energy to move them apart to the same separation.

I haven't even gone near the back of an envelope, but my rough estimate is that tidal effects would have drawn twin worlds apart 1/30 times as much as they have moved the Moon outwards.

The major limiting factors on habitable double-planet sizes and separations to my knowledge:

Roche limit - larger and more massive lobes have a greater minimum separation, so that's that much more energy required for formation.

Tides - more massive lobes inflict greater tidal forces, and larger lobes multiply the effects of the forces inflicted by their partners, reducing habitability.

Formation - the currently favored impact-formation model is much less likely to produce lobes of close order size in the habitable size range.

Opportunity - said impacts are fairly rare despite being inevitable over the course of system evolution because they "use up" at least one of the limited supply of ur-planets in sufficiently eccentric orbits expected to have formed alongsie the sun. This supply could change at any time as observational and computational discoveries chip away at the n-body problem in at least the statistical sense. Scenarios set sufficiently far abroad in time or space might be in latter generation star systems with more plentiful terrestrial planets
due to the abundance of heavy elements from previous stellar generations.

[Flyndaran]

Originally Posted by jeff_wilson

...
Tides - more massive lobes inflict greater tidal forces, and larger lobes multiply the effects of the forces inflicted by their partners, reducing habitability.

Formation - the currently favored impact-formation model is much less likely to produce lobes of close order size in the habitable size range.

...

I lost my data with a computer issue, but the first time I determined tide they weren't that huge.
I know the chance is absurdly high, but not impossible to known physics. I wanted my aliens to have an even rarer situation than we do. It also acted to push their rocketry development much further and faster than earth's. because of that blue-green world sticking int the sky.