Zero orbit always tide locked?

[HG_B]

What about orbit 1? (I seem to recall Mercury is almost tide-locked but has a bit of wobble to it?)

Mercury isn't tide locked.

 

[atpollard]

Mercury isn't tide locked.

But doesn't its orbit and rotation have some resonant relationship?
[making "almost tide-locked" a somewhat valid description]

 

[HG_B]

But doesn't its orbit and rotation have some resonant relationship?
[making "almost tide-locked" a somewhat valid description]

It has a 3:2 rotation/orbit. I don't know if "almost tide-locked" is a scientifically correct term. Due to its high eccentricity orbit it doesn't have the 1:1 ratio. Jupiter also messes with its orbit. Mercury may one day (FAR off into the future) collide with Venus.

 

[lspitz]

I think it's officially called a "spin-orbit resonance" by astronomers, or something along those lines. It's not a tidal lock, and it's only stable if the orbit is reasonably eccentric like Mercury's (although I certainly don't understand all the physics involved myself). It happens when a planet in an eccentric orbit is spinning down towards a true tidal lock due to tidal braking and gets trapped in a local low-energy minimum where there's some whole-number ratio between the planet's sidereal day and its sidereal year.

 

[atpollard]

I think it's officially called a "spin-orbit resonance" by astronomers, or something along those lines.

I figured that somebody had a name for it.
I went to an Engineering University, but they didn't really cover Celestial Mechanics in the Architecture Program.

 

[lspitz]

I figured that somebody had a name for it.
I went to an Engineering University, but they didn't really cover Celestial Mechanics in the Architecture Program.

That may change when buildings get tall enough.

 

[Peter Newman]

I think this will explain the problem

http://www.irregularwebcomic.net/94.html

 

[arbitrary.remora]

This is one of the finest COTI threads in my estimation.

 

[whulorigan]

Planets orbitting Red Dwarfs in Orbit-0 may not be tide-locked

An interesting article in the 02/07/15 issue of Science News:

Rocky planets around cool stars may have Earthlike climates: Atmospheric heating might be the secret to keeping planets spinning.

You will need to have a subscription to read the full article, but the essential premise is that the tug of a star's gravity on a thin atmosphere can keep a planet in a non-tide-locked rotation even while other forces are acting that tend to retard that rotation.

The team in the article used computer simulations accounting for the fact that atmospheric heating at a planet's equator drive winds that cause air to flow toward the cool night-side. The gravitational pull of a star on the planet's atmosphere is a little stronger on the side with more mass, gradually causing the planet to spin faster. According to their modelling, if the Earth were placed in Venus's orbit, the sun's gravitational-tug over time would cause the Earth's rotation to spin-up.

The computer model showed that the gravitational tug on the atmosphere of an Earth-sized world placed in the habitable-zone of an M-type dwarf could be enough to keep the planet spinning in a non-tide-locked rotation.

 

[salochin999]

This sounds great to me.

One of the things about the base system gen is it creates so many worlds that someone decided to colonize at some point yet don't seem to have "made it" (or went backwards at some point).

If the possible variation in tide locked planets are as wide as hinted in this article

http://astrobites.org/2014/11/07/habitability-still-a-go-on-tidally-locked-terrestrial-exoplanets/

then that greatly increases the number of plausible reasons the system stats are the way they are.

Even the least habitable (last on the right)

http://astrobites.org/wp-content/uploads/2014/11/df9_Figure_schematic_diagram_3panels-ygliu.jpg

has plentiful oxygen and water in the ice so domes along the glacier ridge on the equator looks good to me - especially if you imagine (as I do) the earliest expansions having limited Jump so many colonies would have been built as stepping stones between the good planets.

Among the many worlds circling "uninhabitable" stars are:
Ruie, a well-documented world of 7 billion with a standard tainted atmosphere circling an M5V.
Victoria, a well-documented and mapped world of 10 million circling an M6V.
Zila, a well-documented thin atmosphere world of 70 million famed for its wines, circling an M6V.
Porozlo, a world of 20 billion with a standard atmosphere circling an M1V.
Mora, a world of 10 billion with a dense tainted atmosphere circling an M5V.
Riverland, a world of 20 billion with a standard atmosphere circling an M7V.

The "Ancients" can then be used on the hi pop planets with standard atmosphere or those that have already been mapped and then used as hooks e.g. a trip to Porozlo's artificial moon as a crack opens up on the surface leading to (something) or tourist trips to ruined ancients terraforming towers.

The "tainted" part in some of the above list could relate perfectly to this with the night and day part being tainted (in two different ways) and only the equatorial zone okay.

Or the original terraforming breaking down or colonists in domes with decaying automated air and water from the glaciers etc. Pirates hiding out in an abandoned dome.

A lot of the backward planets could be tide locked ones that were colonized as say a J1 stepping stone and later bypassed.

Anyway, seems more like an opportunity than a problem to me so far - although I've only just read about it so could be wrong.

 

[G. Kashkanun Anderson]

An interesting article in the 02/07/15 issue of Science News:

Rocky planets around cool stars may have Earthlike climates: Atmospheric heating might be the secret to keeping planets spinning.

You will need to have a subscription to read the full article, but the essential premise is that the tug of a star's gravity on a thin atmosphere can keep a planet in a non-tide-locked rotation even while other forces are acting that tend to retard that rotation.

Unfortunately, I can't read very much of that article; but the Centauri Dreams website has what appears to be a very extensive writeup and discussion of the original paper, including what has to be one of the most helpful graphs (reproduced from the paper, I assume) that I've ever seen for illustrating the point. Really nice!

The team in the article used computer simulations accounting for the fact that atmospheric heating at a planet's equator drive winds that cause air to flow toward the cool night-side. The gravitational pull of a star on the planet's atmosphere is a little stronger on the side with more mass, gradually causing the planet to spin faster. According to their modelling, if the Earth were placed in Venus's orbit, the sun's gravitational-tug over time would cause the Earth's rotation to spin-up.

Like I said, I didn't read the original article, but the CD writeup seems to say something different -- that the thermal tides will force a planet's rotation to a certain point, but never to where it actually rotates very fast, and also counter to the direction that it orbits. I get the impression that Earth in Venus's position would gradually slow down its counter-clockwise rotation, come to a stop, and then gradually spin up to a very mild clockwise rotation.

The computer model showed that the gravitational tug on the atmosphere of an Earth-sized world placed in the habitable-zone of an M-type dwarf could be enough to keep the planet spinning in a non-tide-locked rotation.

Only some M-type dwarfs, I'm afraid. From the graph, it looks like all K-type stars are covered (and, for that matter, I believe early K-type habitable zones are far enough out to begin with anyway), but only the earliest M-types are covered for Terra-type atmospheres. If you want to include those 10-bar pressure worlds that they mention, then later M-types can be included, but not all of them. It looks like the absolute cutoff is around M4V or so.

But hey! That includes just about all the fusing stars, right? I mean, anything later than M6V is properly a brown dwarf now, anyway.