Random Sci-fi question.

[Graham]

Ok then probably need the physicists for this one but humor me.





would it be possible for two planets say each slightly smaller than the earth to rotate around each other. both spinning whilst also rotating around each other on a centre axis, and at the same time spin around a sun with the centre axis on which they are rotating following an earth type orbit around their sun.


what sort of effect would they have on water masses on each other


G

[grumbledoak]

Can't see any reason why not. And, the water would be attracted to the centre point, so you'd get tides as the planets spin.

[judas]

Yes - they'd both orbit their common centre of gravity. They'd also have to be a fair distance away from each other to stop the orbits decaying and eventually colliding, and also to stop tidal forces pulling each planet to bits. Talking of tidal forces, the difference between low and high tides would be significant to I imagine.

Edited by judas on Sunday 11th October 16:12

[BrassMan]

Been reading The Ragged Astranaughts?

[Graham]

mmm what sort of distance apart. im assuming there must be some sort of equation that would help there... would say 10 times the distance from the earth to the moon be doable ( 2.5 million miles)


although the moon is only 1/80 the earths mass. and im thinking of two similar mass objects

[Graham]

BrassMan said:

Been reading The Ragged Astronauts?

No, but it looks worth a read, although that book seems to bend physics a little...


Im imagining 2 planets with individual atmospheres that would require some form of conventional space travel to get between them.

[s2art]

Graham said:

mmm what sort of distance apart. im assuming there must be some sort of equation that would help there... would say 10 times the distance from the earth to the moon be doable ( 2.5 million miles)


although the moon is only 1/80 the earths mass. and im thinking of two similar mass objects

http://en.wikipedia.org/wiki/Roche_limit

[MartG]

The minimum distance between two bodies orbiting each other before one breaks up is called Roche's Limit - see http://en.wikipedia.org/wiki/Roche_limit

[Graham]

Ta, some interesting reading there..

[TimJMS]

I was immediately put in mind of Janus and Epimetheus, two moons that share orbits around Saturn. It is similar to your hypothesis but not quite the same. Bizarre nonetheless.

[Eric Mc]

Depending on how long the two planets had been orbiting each other, there is a chance that their rotational rates had become locked so that they both presented the same hemisphere towards each other permanently (like the moon does to the earth).