Earthlike double planet orbit and tides

[Junghalli]

I'm designing a binary pair of Earthlike planets (another project of mine) and basically want somebody to tell me whether my assumptions hold up.

The planet is supposed to have a combined mass of maybe 1.5 Earths (so ~.7 Earth masses each), orbit a K class star at around .5-.6 AU, and orbit each other close enough so they can be mutually tidally locked and still have a relatively Earthlike day/night cycle (maybe 30 hours or so) - so the orbital seperation is around 40-50,000 km. So, I'm thinking:

1) Such a close orbit would be pretty stable.
2) Tidal interactions between the planets would very effectively circularize their orbits. The eccentricity of their orbit would be extremely small.
3) The solar tide (which at this orbit would be somewhat stronger than Earth's lunar tide) would tend to slow the rotation of both planets, which would result in them gradually spiralling toward each other over billions of years while pretty much maintaining tidelock.

2 especially concerns me. While the planets would be mutually tidelocked the expansion and contraction of the distance between them with orbital eccentricity would still raise tides, and given how close the planets are these would be humongous if eccentricity was significant. I figure the mechanism described here would maintain a circular orbit pretty effectively, but that's just a guess.

I tried simulating the system with Gravity Simulator and I got a rather elleptical orbit ... but does Gravity Simulator take stuff like tidal circularization into account?

So, anybody know whether my assumptions are right and I could realistically get a pretty much Earthlike planet this way?

Thanks.

[Feil]

If you're looking for a planet with indigenous higher-order life, I'm pretty sure that leading theories of the evolution of life on Earth reserve a pretty important role for earth-like tides, so your tide-locked system might have trouble with that. Similarly, tides have a significant impact on plate tectonics and volcanism. I'm not sure whether a tide-locked system like the one you propose would have more or less tidal heating, but it would certainly behave differently than Earth does, at least. This article might be a little bit useful. http://uanews.org/node/21820

Sorry I can't be much help, but I barely qualify as an interested layman in the relevant fields.


EDIT: As long as you don't include tidal heating and deformation - i.e. you assume a perpetual motion machine - this planetary system should be pretty easy to model in math software (MATLAB, R, Mathematica) or even a general-purpose programming language like C. Given masses, Newton's law of gravitation, and initial velocities and positions, you should be able to work a little bit of calculus to find where your planets will be in an hour, a day, or a billion years.