I've started trying to dispose of the boxes of books I have stashed around the house. This, of course, leads to re-reading. In a David Brin story from the 1980's he depicts a double planet with both of the planets being earth-like. That is, the planets are orbiting each other while orbiting their parent star. I'm wondering if such a system is possible. Could it be stable? In his story, Brin depicts both planets as evolving intelligent life.

I understand that Earth-Luna "almost" qualifies as a double planet, but for the fact that the gravitational center of the orbit lies inside the volume of the earth. And in Brin's scenario, tidal effects on both bodies would presumably be spectacular.

Any thoughts?

---

“Upon opening the box, Schroedinger's raccoon will be observed in one of three possible states; alive, dead, or really, really pissed off.”

it is possible. gemini, the twin stars, i think they rotate around each other and rotate around their galaxy. according to the ancient sumerians, planets are stars, just smaller and cooler.

It seems that twin planets could orbit one another stably, under certain circumstances. They would eventually become mutually tidally locked, the same sides always facing each other, like Pluto and its moon Charon. This would cancel out any changing tidal effects. Linked article, below, has more details on this:

http://www.space.com/27832-binary-earth-size-alien-planets.html

It seems that twin planets could orbit one another stably, under certain circumstances. They would eventually become mutually tidally locked, the same sides always facing each other, like Pluto and its moon Charon. This would cancel out any changing tidal effects.

Thank you, Michael. Very interesting article. And yes, I wondered about tidal lock, too. Not to criticize Brin (SF is fiction, after all) but I don't believe the planets in his story were locked.

---

“Upon opening the box, Schroedinger's raccoon will be observed in one of three possible states; alive, dead, or really, really pissed off.”