Tidally Locked...To What?

[Reido]

I've been trying to wrap my head around the term "Tidally Locked" in the system menu.

I understand what it means for single bodies in that they always show the same face to the body they're orbiting, such as our Moon, but what does that term mean exactly when it comes to binary planets or moons of moons when BOTH of those are listed as "Tidally Locked"?

Does it just mean that they're tidally locked to each other? or that they're BOTH tidally locked to the major body that they're orbiting?

The second option just doesn't seem to make sense, but I thought I'd ask as sometimes things are stranger than we can imagine, or the Stellar Forge needs some tweaking


Andrew

 

[Kancro Vantas]

I've been trying to wrap my head around the term "Tidally Locked" in the system menu.

I understand what it means for single bodies in that they always show the same face to the body they're orbiting, such as our Moon, but what does that term mean exactly when it comes to binary planets or moons of moons when BOTH of those are listed as "Tidally Locked"?

Does it just mean that they're tidally locked to each other? or that they're BOTH tidally locked to the major body that they're orbiting?

The second option just doesn't seem to make sense, but I thought I'd ask as sometimes things are stranger than we can imagine, or the Stellar Forge needs some tweaking


Andrew

Tidally Locked to each other. It is the only way to keep their mini system stable. The bodies have to be on opposite sides at all moments..so they are orbiting around the barycenter at same speed, otherwise, if they come to the same side, they "fall off" orbit, smashing and destroying each other or falling together into the bigger planet.

 

[Reido]

Thanks, that's what I thought.

I've been spinning them around in my head and it didn't make sense to have it any other way without things going pear shaped real fast.


Andrew

 

[Allitnil]

"Tidally locked" means that the same part of the body faces the body it is orbiting, it's got nothing per se to do with the barycentric bit. It is worth pointing out that all the bodies in a system (whether that be a full solar system, the Earth & Moon or two arbitrary planets) orbit around the system's barycentre although in ED terms we use it to refer to two or more bodies with masses close enough to each other that it doesn't fit into an 'obvious' planet / moon relationship. See the first two animations at http://en.wikipedia.org/wiki/Barycentric_coordinates_(astronomy)#Animations

In the case of two planets in a barycentric orbit, ED gives data related to that orbit (semi-major axis, orbital period). So it's reasonable to assume that in those cases, the bodies are tidally locked to each other.

For moons of moons I would expect that the first moon is tidally locked to the planet and the second moon is tidally locked to the first one.

 

[Jackie Silver]

Pluto and Charon are tidally locked to each other IIRR.

 

[Reido]

Ok, I've been doing some more mental visualizations and I can now picture how a moon and it's moon can both be tidally locked.

The big moon always shows the same face to the planet while the small moon will orbit the big moon but also only show the same face to the big moon.

In the case of binary planets where both are listed as tidally locked the only thing that makes sense is that they're tidally locked to each other and showing the same face to each other as they're both orbiting a common center of mass.

I think that's sorted.

Thanks for the help everyone, working through it helped me get a handle of what's going on. I guess I can remove those questioning comments from my spreadsheet


Andrew

 

[Poseidal]

Makes me wonder.

On a planet that's tidally locked to its moon (or in binary orbit with another small planet), so that in one region you will see there is a constant moon / object in the sky and on the other side of the world you would never see it.

What kind of cultures could develop, or what could happen around it?

Especially if it is a weird looking partner.