Zero orbit always tide locked?

[SpaceBadger]

Has it been decided that worlds in orbit 0 are always tide-locked? (In this case, the star is a K6 V, if that matters.)

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

 

[SpaceBadger]

And a semi-related question: system has two M stars, either of which would have a habitable zone in orbit 0. What about if I say that the two stars are in a close orbit of each other, could the planets in the system have an orbit around the pair rather than around one or the other? The two M stars are both size V (main sequence), so should be of similar size to each other.

What would be a guess on appropriate habitable zone orbit around such a twin-M?

 

[SpaceBadger]

I'm not sure whether to be happy or not that whoever generated the star data for Daibei sector appears to have used a realistic distribution of stellar spectrum types, meaning a lot of M stars and therefore a lot of tide-locked mainworlds in inner orbits. I guess trying to follow our understanding of reality is a good thing, right?

 

[SpaceBadger]

I seem to be talking to myself here, but maybe someone else will have a similar question and be helped by this.

I tried some different search terms and found these two threads:

Why are Red Stars so common?

Close binary red dwarf system: habitable zones, tidal locking

From reading these, it appears that the answers to my earlier questions are:

Orbit 0 is always tide-locked, but may be nicely habitable if conditions are right (standard or dense atmosphere) to allow distribution of temperatures and prevent atmo from freezing out into snow on the cold side.

Still did not see an answer on Orbit 1. There was some info about Mercury's 3:2 ratio preventing total tide-lock, but I'm not sure if this is due to it being in Orbit 1 rather than Orbit 0 (we don't have anything in Orbit 0 in Solar System), or some other factor.

Close orbiting binaries are to be added together for mass in determining orbital characteristics of planets, and have luminosity added together in a more complicated way that I need to re-read for determining habitable zones. But yeah, the resulting hab zone is probably further out than Orbit 0, so may avoid tide-lock.

 

[Cryton]

Red Stars (type M) are more common because generally because they are smaller, take less stellar gasses to form, and due to their smaller size, burn cooler, and longer than other types of stars.

~Cryton

 

[SpaceBadger]

Red Stars (type M) are more common because generally because they are smaller, take less stellar gasses to form, and due to their smaller size, burn cooler, and longer than other types of stars.

Yeah, I got that. (I wasn't the one asking "Why so common?", that was a different thread.)

I was just musing over the effect of accurately reflecting this fact in generating star systems, resulting in so many habitable worlds that are tide-locked and thus not exactly what we Earth folk are accustomed to.

 

[shaunhilburn]

What would be a guess on appropriate habitable zone orbit around such a twin-M?

There is more variation over spectral class M than there is over the remainder of the main sequence. An M2V star is not anything at all like an M7V star; they're completely different beasts. The M-dwarf habitable zone depends on the precise spectral class.

 

[SpaceBadger]

There is more variation over spectral class M than there is over the remainder of the main sequence. An M2V star is not anything at all like an M7V star; they're completely different beasts. The M-dwarf habitable zone depends on the precise spectral class.

Thanks. Does the usual interpolation from the examples given in the stellar tables work for M stars?

I recall reading in your earlier thread that there was some complication beyond simply adding the luminosities to determine hab zone; guess I need to go back and re-read that bit.

One of the examples that I need to work with was an M0 V and an M6 V.

 

[aramis]

You need sufficient lightfall to heat the surface to liquid ammonia through liquid water ranges; internal heat radiating out can provide additional.

But you also should account for other solar phenomena... anything close enough to be tidelocked may be hit with enough particle flow to make it hard to hold an atmosphere. Also, a star that's radiation is centered in the near IR will produce different heating patterns on worlds with water than one that's mostly in the yellow or mostly in the blue.

 

[shaunhilburn]

Thanks. Does the usual interpolation from the examples given in the stellar tables work for M stars?

I recall reading in your earlier thread that there was some complication beyond simply adding the luminosities to determine hab zone; guess I need to go back and re-read that bit.

One of the examples that I need to work with was an M0 V and an M6 V.

You should derive the habitable zone for a solitary star from R^2T^4, where R is stellar radius (sun=1) and T is photosphere effective temperature (sun=1). This yields the bolometric luminosity (this is *not* the brightness/visual luminosity). The earth-equivalent distance is the square root of the bolometric luminosity.

The habitable zone for two closely separated stars is derived from the sum of their bolometric luminosities.

        M7V     M2V      R^2      T^4          Lb
R       0.12    0.45     0.0144    0.041    0.00059049
T       0.47    0.55     0.2209   0.0915    0.020213731

In this example, sum the bolometric luminosities and take the square root. You get 0.144 AU. This approximation works well for closely spaces stars and becomes less accurate as the separation increases.

 

[whulorigan]

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

Mercury is in a 3:2 orbital resonance. It rotates on its axis 3 times for every 2 revolutions about Sol. That means it operates like a harmonic oscillation in terms of energy transfer, so the orbit/rotation rates are stable. Several moons around gas giants in the Solar System (see Galilean Moons) have similar orbital resonances. So orbital resonance may not necessarily be a rare phenomenon in the galaxy.

 

[SpaceBadger]

OK, suppose an M5 V star w multiple planets, including planets in both Orbit 0 and Orbit 1.

Could both of those inner planets be tide-locked to the primary, or only the innermost?

How does one determine how far out in orbits from a particular mass of star the planets will (or could) be tide-locked?

 

[rancke]

Has it been decided that worlds in orbit 0 are always tide-locked? (In this case, the star is a K6 V, if that matters.)

By coincidence I've just been working with a world orbiting a K6 V star. The star was originally a K6 III (or a K6 II -- the canonical data has it both ways), but as the previously published information about it didn't mention a several week in-system trip from the solar jump limit to the world, I decided to make it a main sequence star. But I kept the K6 part -- a one-day trip from the jump limit wouldn't hurt, I thought.

Then someone pointed out to me that this allegedly Earthlike world with the almost Earthlike day would be tidelocked. I considered making it a G6 star instead, but in the end I decided just to say that the world wasn't tidelocked, with no explanation. The local galactographers blame the Ancients, of course. Maybe they're right.

Even if you don't like to treat the laws of astronomy that disrespectfully, the Ancients can be an out for you. If they terraformed your world, speeding up the rotation in the process, the world will keep spinning for a long long time before becoming tidelocked again. I dislike invoking the Ancients unless absolutely necessary, but I dislike a plethora of tidelocked worlds even more. A handful of tidelocked worlds is fine, but about one third (guesstimate) of the worlds in Charted Space? No.


Hans

 

[shaunhilburn]

OK, suppose an M5 V star w multiple planets, including planets in both Orbit 0 and Orbit 1.

Could both of those inner planets be tide-locked to the primary, or only the innermost?

How does one determine how far out in orbits from a particular mass of star the planets will (or could) be tide-locked?

It's safe to say that all planets within 0.5 AU of an M5V star are tide locked. Tidal braking and locking are complex topics; whether a body is tide locked depends on things like star mass, system age, as the planet's size, rigidity, mass, and ocean coverage. Given enough time, all orbiting bodies eventually become tidelocked to their parent.


You can estimate the tidal braking force by calculating the magnitude of tidal effect, which is proportional to M/AU³.

The tidal force on an Earth-sized planet orbiting an M5V star (M = 0.2 solar masses) at 0.585 AU is the same as solar tide on Earth.

(Note that the sun only exerts 46% of the moon's tide-raising force on Earth)

 

[SpaceBadger]

Even if you don't like to treat the laws of astronomy that disrespectfully, the Ancients can be an out for you. If they terraformed your world, speeding up the rotation in the process, the world will keep spinning for a long long time before becoming tidelocked again. I dislike invoking the Ancients unless absolutely necessary, but I dislike a plethora of tidelocked worlds even more. A handful of tidelocked worlds is fine, but about one third (guesstimate) of the worlds in Charted Space? No.

Good point, Hans. And sometimes I think that really, this level of detail matters most to us GMs, who want to be running a somewhat consistent Universe. Most players just want a fun place to have adventures.

 

[SpaceBadger]

It's safe to say that all planets within 0.5 AU of an M5V star are tide locked. Tidal braking and locking are complex topics; whether a body is tide locked depends on things like star mass, system age, as the planet's size, rigidity, mass, and ocean coverage. Given enough time, all orbiting bodies eventually become tidelocked to their parent.


You can estimate the tidal braking force by calculating the magnitude of tidal effect, which is proportional to M/AU³.

The tidal force on an Earth-sized planet orbiting an M5V star (M = 0.2 solar masses) at 0.585 AU is the same as solar tide on Earth.

(Note that the sun only exerts 46% of the moon's tide-raising force on Earth)

Thanks, Shaun!

 

[Fovean]

By coincidence I've just been working with a world orbiting a K6 V star. The star was originally a K6 III (or a K6 II -- the canonical data has it both ways), but as the previously published information about it didn't mention a several week in-system trip from the solar jump limit to the world, I decided to make it a main sequence star. But I kept the K6 part -- a one-day trip from the jump limit wouldn't hurt, I thought.

Then someone pointed out to me that this allegedly Earthlike world with the almost Earthlike day would be tidelocked.

Ah, Heya... why do I love love thee so?

I prefer the GURPS approach of determining a star's orbital distances and life zones in AU, the canonical fixed orbits make a mess of everything IMO. I suspect that someday someone will publish something more realistic (or even up-to-date), hopefully playable, and less confusing/frustrating than the several extant rule sets out there for Traveller players today.

 

[SpaceBadger]

Even if you don't like to treat the laws of astronomy that disrespectfully, the Ancients can be an out for you. If they terraformed your world, speeding up the rotation in the process, the world will keep spinning for a long long time before becoming tidelocked again. I dislike invoking the Ancients unless absolutely necessary, but I dislike a plethora of tidelocked worlds even more. A handful of tidelocked worlds is fine, but about one third (guesstimate) of the worlds in Charted Space? No.

I've been thinking about this, and I'd prefer to just ignore the science than to fall back on The Ancients Did It.

Yet another nod to "hard SF realism" falls to the wayside, kicked into the gutter by the desire to tell some good stories.

Sigh. It gives me more good colony worlds for the Vilani, yet the decision is still slightly bittersweet.

 

[SpaceBadger]

I prefer the GURPS approach of determining a star's orbital distances and life zones in AU, the canonical fixed orbits make a mess of everything IMO. I suspect that someday someone will publish something more realistic (or even up-to-date), hopefully playable, and less confusing/frustrating than the several extant rule sets out there for Traveller players today.

You'll still have to deal with a lot of "life zone" planets around M and K stars being tide-locked. The "hard SF" solution is to start w the physical characteristics of your star systems, then decide where people would want to live. Some would choose the tide-locked worlds, but probably not so many as in the OTU.

The problem with the Traveller way of doing it is that we randomly generate all of these populated worlds and then try to make sense of them. Sometimes that is fun, sometimes (as Hans noted) you end up with approximately one-third of your mainworlds tide-locked to small red stars.

 

[shaunhilburn]

sometimes (as Hans noted) you end up with approximately one-third of your mainworlds tide-locked to small red stars.

You say it like it's a bad thing.


M-dwarfs are the largest population of stars, it follows that a large percentage (may be most) of the shirtsleeve worlds will orbit them. I think that as more data is collected, we'll find that life-bearing worlds that rotate freely are the exception. A COTI poster once said "It's a tide-locked universe."