"Twin planets" and tide-locking

[EternalFrustration]

Putting out the call to any astrophysics experts:
Suppose you have two planets, each about 1 Earth mass, orbiting around a barycenter. The average distance between the two planets is a little under 500,000 km. Would they tide-lock to each other, or would they still be able to rotate independently?

 

[tblaxland]

I can't see why the wouldn't tide lock each other. Both objects are still subject to a gravity gradient across them :shrug:

 

[Quick_Nick]

Those would be some intense tides! That's around the distance to the moon but with earth masses.

 

[agentgonzo]

Yes, they would both tidally lock over time. If they had identical compositions they would eventually tidally lock at the same time, but if not one would get locked before the other.

 

[Quick_Nick]

Their distance should change as they lock. If your species is on one of these planets, you better hope they're drifting apart.
Maybe someone wants to do the math, but I think the tidal forces will produce results like Io.

 

[Fizyk]

The way the distance changes depends on the direction the planets are rotating. For example, the Moon is drifting away from Earth, because it has a prograde orbit and in a way it steals the Earth's angular momentum. If it was in a retrograde orbit, it would get closer and closer - the Earth would have to take some angular momentum from the Moon in order to stop rotating.

 

[EternalFrustration]

I am shocked to discover that the BSG writers may have gotten some bad science in there :rofl:

 

[agentgonzo]

Their distance should change as they lock. If your species is on one of these planets, you better hope they're drifting apart.

Tidal locking takes place over timescales vastly larger than the total lifespan of a specific species. The species likely evolve into something else by the time a noticeable change in the planets has occurred.

 

[evilfer]

The way the distance changes depends on the direction the planets are rotating. For example, the Moon is drifting away from Earth, because it has a prograde orbit and in a way it steals the Earth's angular momentum. If it was in a retrograde orbit, it would get closer and closer - the Earth would have to take some angular momentum from the Moon in order to stop rotating.

In the case the Moon were in retrograde orbit, in the process of Earth-Moon locking, would the Earth's rotation be null for some time? That'd be tough.

In this case, when the Earth's rotation is aproximately null, I can imagine the effect of Sun-Earth tidal locking would be very strong. I guess it would eventually lock the Earth rotation to the Sun, stoping the Earth locking with the Moon.

Sorry for the digression . Wouldn't the same happen in the case of two Earths in retrograde orbit around each other (but prograde around the Sun)?