Check out my avatar. I spent about five minutes rotating and pasting a picture of earth below a picture of venus. Is it possible for a double planet system like this to exist? With one world like ours and another completely inhosbitable [to us]? What would the conditions of their orbit be like, assuming that they orbited a relative circle around their star?

My idea was that the worlds were connected by a single tower, and that their orbit would be changed to that of one planet, so instead of rotating as individual worlds their rotations (day and night, not yearly orbits) are really nonexistent. It's hard to put into words, but think of two balls connected by a meter stick or something. Hold the stick in the center, and swing it around your head. The balls, individually do not move, but rather, they still rotate as one, and as such they still have day and night cycles.

Is this enough for you all to answer my questions? If not, I'll try again.

1) I don't believe they'd be able to exist that close to another. I'm not sure how Roche's limit would be affected being similar sizes, but the closer they are, the more likely they will break apart from the tidal stresses.

2) As far as being a double planet, the Earth-Moon system is sometimes referred to such a name, even though the Moon is smaller. The center of rotation of this system is still way inside the Earth, so it seems to us that the Moon is going around, when in fact they both are orbiting. So, increase the mass of the Moon, and the center will move out.

3) Rotation - eventually they'd get tidal locked, but a tidal locked system like you have would be too long I think to support life. The atmosphere would not be able to hold onto its heat for even half of a lunar rotation, and any closer to speed up the orbit would go back to point 1). But if you have them rotating as Earth does, while having a long orbital period, that should work. They'd have long frequent eclipses...

But if you have them rotating as Earth does, while having a long orbital period, that should work. They'd have long frequent eclipses...

Rotating individually? That I cannot do...

When you say long orbital period, you mean orbital-around-the-sun, right? That is doable.

If they were as close as pictured, or even closer, would there be any funky gravitiational effects, like erupting volcanoes, earthquakes etc? The thing is, it's for a fantasy book, so science only makes a partial difference, I was just curious:)

Thanks.

As close as depicted, the Roche limit would tear them up.

Alright, thanks. Guess I'll just have to leave it up to magic to keep them from being ripped to shreds...

Wait a second, does it matter if one of them didn't form anywhere near the other? If it had shifted its orbit, so as to connect to the other, would that make any kind of difference?