Zero orbit always tide locked?

[rancke]

You say it like it's a bad thing.

That's because we think it is.

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."

A game universe is suposed to be a setting for running fun games, not a realisitc simulation. There are a few tidelocked worlds in Science Fiction literature (at least, I'm pretty sure there must be, even though I can't think of any examples off-hannd), but the vast majority of worlds are more familiar to the reader than that.

It may be a failure of imagination on my part, but I find it easier to write up worlds that are livable in more than a thin belt around the middle.


Hans

 

[lspitz]

That's because we think it is.



A game universe is suposed to be a setting for running fun games, not a realisitc simulation. There are a few tidelocked worlds in Science Fiction literature (at least, I'm pretty sure there must be, even though I can't think of any examples off-hannd), but the vast majority of worlds are more familiar to the reader than that.

It may be a failure of imagination on my part, but I find it easier to write up worlds that are livable in more than a thin belt around the middle.


Hans

Under the right circumstances, a tidally locked world can have as much habitable land area as Earth. There's also a fascinating amount of variation possible depending on how much water is in the oceans. I would not write off the planets of red dwarf stars as boring so easily.

To answer a more general question posed back at the beginning of the thread: Numerical simulations have been consistently saying for fifty years that any more-or-less Earthlike planet orbiting a star of roughly 0.7 solar masses or less is going to be tidally locked to its star (or in a whole-number spin/orbit resonance like Mercury, if its orbit is eccentric) by the time complex life evolves. The spin-down due to tidal forces takes at most two to three gigayears, and very often much less. This covers the later K types, and it is guaranteed that any planet in the life zone of a M-class red dwarf will be tidally locked or in a spin/orbit resonance.

 

[rancke]

Under the right circumstances, a tidally locked world can have as much habitable land area as Earth. There's also a fascinating amount of variation possible depending on how much water is in the oceans. I would not write off the planets of red dwarf stars as boring so easily.

I'm not. I'm writing it off as something I myself personally would not be able to make non-boring writeup of in the numbers we're talking about here (I'd back my imagination to come up with a number of interesting tidelocked worlds if I had the motivation. But one-third of the worlds in Charted Space? Or even just the Spinward Marches? I don't think so).

But that doesn't mean I'd mind in the least if you went ahead and wrote up some non-boring tidelocked worlds. Just not Heya, eh?


Hans

 

[lspitz]

I'm not. I'm writing it off as something I myself personally would not be able to make non-boring writeup of in the numbers we're talking about here (I'd back my imagination to come up with a number of interesting tidelocked worlds if I had the motivation. But one-third of the worlds in Charted Space? Or even just the Spinward Marches? I don't think so).

But that doesn't mean I'd mind in the least if you went ahead and wrote up some non-boring tidelocked worlds. Just not Heya, eh?


Hans

If you are into painfully accurate realism, then 73% of the worlds in Charted Space should be tide-locked planets of red dwarf stars. I don't think canon can be bent that far to accommodate reality.

A number of new studies have been published in the past year or two on the climates of tide-locked planets (including some important work on their internal geodynamos due to tidal flexing). Some really cool and exciting stuff. I may try my hand at designing a world or two, maybe one at the wet end of the continuum, one at the dry end, and one in the middle. And maybe one with an eccentric orbit and a 3:2 or 4:3 spin/orbit lock, just for fun.

 

[atpollard]

I am coming late to this dance, so sorry if this has already been mentioned, but IIRC the greatest threat to life around a red star is the earlier phases of the star that blast away the atmospheres and scorch the surface to molten rock before the 'liquid water' zone moves inward to a tidally locked orbit.

Anything that survives the stellar evolution, will probably eat both you and the ship you flew in on.

 

[whulorigan]

I am coming late to this dance, so sorry if this has already been mentioned, but IIRC the greatest threat to life around a red star is the earlier phases of the star that blast away the atmospheres and scorch the surface to molten rock before the 'liquid water' zone moves inward to a tidally locked orbit.

Anything that survives the stellar evolution, will probably eat both you and the ship you flew in on.

Red Dwarfs have a high probability of being Flare Stars, if that is what you mean. Which is especially problematic for planets in Inner Orbits.

 

[atpollard]

Sorry, I was misremembering the life cycle of White Dwarfs where they pass through a red giant phase before settling back down to dwarf size.

 

[lspitz]

As I understand the literature on the subject, red dwarfs are flare stars in their younger days. By the time complex life evolves and moves out of the seas onto land where it would be vulnerable to flare radiation, the flare part of the star's life cycle is over.

I've never run across any papers suggesting that atmospheric erosion during the flare phase will be significant for planets in the habitable zone. Even if it were, a secondary atmosphere could be outgassed by the planet itself after the flares die down. If the planet's orbit is eccentric to any degree, tidal flexing will create powerful volcanism to speed the outgassing process. In fact, it is thought that tidal flexing may put a limit on habitability of planets of red dwarf stars in orbits that deviate significantly from perfect circularity; beyond a certain point, it's just too much of a good thing and the constant eruptions become destructive to any nascent biosphere.

 

[Carlobrand]

Okay, help me out here, 'cause I'm just realizing this is a problem.

I'm hearing that M dwarfs are the most common type of star. That I know.

I'm seeing from Book 6 that main sequence Ms don't have a habitable zone, aside from the M0's, the largest ones. The M0's, you have to be in orbit at 20 million klicks or so to be habitable. So, large chunks of the Traveller universe cannot have habitable planets. Yet, they do.

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.

Now, we could toss out the orbital zone rules - they seem to belong to outdated science - and declare that these worlds are within a few million klicks of their pathetically weak suns. And then tidal-lock them. However, I think someone on Ruie or Victoria would have noticed if they were on a tidally locked world.

Traveller came up in the era that followed the success of Star Wars. As much as it tried to aim for some level of sci-fi realism, its writers were clearly not thinking in terms of 3/4 of the Imperium being on tidally locked worlds circling glowing red coals - and Spinward Marches Campaign
s effort to retrofit the Marches to that idea was clearly a flop. The Traveller Imperium, like the universe of Star Wars, like the universe of Star Trek really, is a shirtsleeve universe of alien but earthlike worlds, most of them - in defiance of the odds - conveniently breathable and conveniently habitable by humans. One could choose to make a hard sci-fi setting where 2/3 of the planets were tidally locked or in some harmonic around some red coal-star, and I think it would be a really neat place (but I might point out that a good number of them won't have an O2 percentage conveniently within human norms). However, that's not the setting we've been handed.

If we were to go hard science with the stars, we'd really need to rewrite the world generation worlds to make them more hard science as well. More worlds with nonbreathable CO2 or methane atmospheres. Worlds with insufficient O2 concentrations for unassisted breathing. And of course lots and lots of tidally locked worlds ranging from uninhabitable without technological assistance to barely habitable.

 

[SpaceBadger]

We already take liberties with the galaxy in which we play Traveller. It is supposed to be our own galaxy - at least, Terra of Sol appears in it, and shares some of our history - and yet it is strangely flat, two-dimensional for mapping purposes, whereas our galaxy clearly has at least three dimensions.

Maybe the key is to not try to match the frequency of stars on the maps with our real galaxy, and simply assume that lots of M class stars do not appear on the map and are unimportant. If you are generating your own sectors, simply alter the tables (or algorithms) so that you don't get any M class, or very few. Bingo, no M class stars, no tide-lock problem (well, some K class, but not nearly so many).

The problem is that we are trying to use all of these published sources which do include lot of M class stars. (We didn't use to have a listing of star type for every system. I think maybe that came in with MT?) I think the simpler path, if one wants to use the published materials, is to simply ignore the physics of the matter and not make all of those worlds tide-locked. A few scattered here and there for color and novelty are great, but not a huge percentage of inhabited worlds in the OTU.

 

[SpaceBadger]

Just had another thought on the preceding. Maybe it is Jump that needs to be messed with. Maybe it works more like in Jerry Pournelle's stories, with jumplines created between stars based on stellar mass and a bunch of other variables. Maybe M class stars simply lack the mass to make jumplines, so are not included on the maps, because unless you go STL you can't get there from here. No need to alter maps and actually draw in jumplines (unless you want them). Just assume that all systems within reach of your jumpdrive are connected, and that you don't see systems that you can't reach.

 

[mike wightman]

How do you explain jumping to empty hexes then?

 

[lspitz]

I've also considered Spacebadger's approach to explain the scarcity of M-type stars on the maps, but it does conflict with canon and raises all those nasty questions about how you can jump to an empty hex. Haven't come up with a good rubber-science justification to explain this, so I haven't pursued the idea.

 

[whulorigan]

Maybe the key is to not try to match the frequency of stars on the maps with our real galaxy, and simply assume that lots of M class stars do not appear on the map and are unimportant. If you are generating your own sectors, simply alter the tables (or algorithms) so that you don't get any M class, or very few. Bingo, no M class stars, no tide-lock problem (well, some K class, but not nearly so many).

I have always presumed that the starmaps we have in Traveller are astrogators' Jump-maps, not astronomical digital surveys. Systems are listed on the maps because there is at least some reason to go there (no matter how minor). Stars which have NO redeeming value (i.e. no resources/worthwhile worlds, no population, and with no gas giants for refueling) may very well be left off the maps altogether. In fact, some stars may have no planets at all (possibly a mere scattering of uninteresting meteoroids and asteroidal debris).

I'm seeing from Book 6 that main sequence Ms don't have a habitable zone, aside from the M0's, the largest ones. The M0's, you have to be in orbit at 20 million klicks or so to be habitable. So, large chunks of the Traveller universe cannot have habitable planets. Yet, they do.
.
.
.

Now, we could toss out the orbital zone rules - they seem to belong to outdated science - and declare that these worlds are within a few million klicks of their pathetically weak suns. And then tidal-lock them.

This is one possible realistic solution for some systems.

. . . a shirtsleeve universe of alien but earthlike worlds, most of them - in defiance of the odds - conveniently breathable and conveniently habitable by humans. One could choose to make a hard sci-fi setting where 2/3 of the planets were tidally locked or in some harmonic around some red coal-star, and I think it would be a really neat place (but I might point out that a good number of them won't have an O2 percentage conveniently within human norms). However, that's not the setting we've been handed.

If we were to go hard science with the stars, we'd really need to rewrite the world generation worlds to make them more hard science as well. More worlds with nonbreathable CO2 or methane atmospheres. Worlds with insufficient O2 concentrations for unassisted breathing. And of course lots and lots of tidally locked worlds ranging from uninhabitable without technological assistance to barely habitable.

Several things to consider here that have been touched on:

1) O₂ is a highly reactive chemical. No planet will have any free O₂ in its atmosphere unless there is some active process that is generating it (or that has had some such process in the recent past, astronomically speaking). On Earth, that process is photosynthesis. On other worlds, a similar byproduct of a life process or other naturally occurring chemical/geological process generating O₂ would be necessary. Likewise, colonists/terraformers could introduce such a process in order to generate the O₂ (over time) to the levels they desire. Therefore, if the process is not natural, then there is either current terraforming at work, or there is remnant terraforming by a previous intelligence (probably the Ancients). This could also explain some of the tainted atmospheres as worlds where the Ancient terraformers influence has been removed, and the atmosphere is slowly returning to its original conditions, or is finding a new equilibrium point. Otherwise, atmospheres will be composed of inert chemicals that can exist at the particular temperature/pressure/gravity in question (i.e. "Exotic" atmospheres). Remember, the Ancients had 20,000+ years to fiddle with the worlds of charted space, and (more recently) Humaniti has had 10,000 years (albeit at lower tech-levels) to do the same.

2) Even if there is native life producing O₂, it is not likely to be doing so at levels that Humans find comfortable. The life in question will be adapted to the atmospheric conditions native to the world. Humans would still likely need compressors or filters to adjust the gas-mix.

3) Unless there is canon to the contrary for a particular world, just because a world is listed with a "breatheable" atmosphere does not necessarily mean that the temperature of the planet is within human-desirable norms. A world could have a "standard" N₂/O₂ atmosphere and 50% hydrographics, and yet still be -40 ^oC temperature at the equator during the summer, with ice-capped oceans. IISS Survey Data is sometimes notoriously "incomplete" when looking at the UWP data alone.

​

While I generally agree with Ranke that "the Ancients are responsible" excuse can definitely get overused, in this particular instance I do not think it is something that you can get around, as they (as well as intelligent sophonts later) definitely did tinker with many of the worlds of Charted Space. A combination of my above comments with SpaceBadger's thought that "irrelevant" stars are not listed on the Jump-charts is probably the best solution short of going to the work of creating a 3I-based ATU.

Of course, you could always introduce 3D-starmapping into your Universe and add "layers" of stars above/below the Traveller map-plane that are totally free for the GM to develop . . .

 

[lspitz]

Okay, help me out here, 'cause I'm just realizing this is a problem.

I'm hearing that M dwarfs are the most common type of star. That I know.

I'm seeing from Book 6 that main sequence Ms don't have a habitable zone, aside from the M0's, the largest ones. The M0's, you have to be in orbit at 20 million klicks or so to be habitable. So, large chunks of the Traveller universe cannot have habitable planets. Yet, they do.

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.

Now, we could toss out the orbital zone rules - they seem to belong to outdated science - and declare that these worlds are within a few million klicks of their pathetically weak suns. And then tidal-lock them. However, I think someone on Ruie or Victoria would have noticed if they were on a tidally locked world.

Traveller came up in the era that followed the success of Star Wars. As much as it tried to aim for some level of sci-fi realism, its writers were clearly not thinking in terms of 3/4 of the Imperium being on tidally locked worlds circling glowing red coals - and Spinward Marches Campaign
s effort to retrofit the Marches to that idea was clearly a flop. The Traveller Imperium, like the universe of Star Wars, like the universe of Star Trek really, is a shirtsleeve universe of alien but earthlike worlds, most of them - in defiance of the odds - conveniently breathable and conveniently habitable by humans. One could choose to make a hard sci-fi setting where 2/3 of the planets were tidally locked or in some harmonic around some red coal-star, and I think it would be a really neat place (but I might point out that a good number of them won't have an O2 percentage conveniently within human norms). However, that's not the setting we've been handed.

If we were to go hard science with the stars, we'd really need to rewrite the world generation worlds to make them more hard science as well. More worlds with nonbreathable CO2 or methane atmospheres. Worlds with insufficient O2 concentrations for unassisted breathing. And of course lots and lots of tidally locked worlds ranging from uninhabitable without technological assistance to barely habitable.

Yes, the fixed Titius-Bode orbit rule based on Sol System is the real culprit. Habitable zone orbits are certainly possible for the smaller red dwarf stars in the real universe, but not in the OTU because of this rule. There was no good reason to suppose that every planetary system in the universe would be arranged and scaled exactly like Sol System (and several good reasons to think that they wouldn't) even way back when the rule was written, but it did make things very simple and didn't take up a lot of page space. No equations for the math-phobic to angst over, just a lookup table. A big plus for those who just wanted to get on with the game and not worry about it, and a big minus for the world-building gearheads.

Planets like Ruie and Zila should be tide-locked or, at best, locked into a whole-number spin/orbit resonance à la Mercury that gives them extreeeeeemely long days and nights (ameliorated a little, compared to Mercury, by the short length of the year). If canon says otherwise for these worlds, there's no good way to reconcile this with modern astrophysics.

I suppose you can argue that tidally locked planets of red dwarf stars might average less oxygen in their atmospheres because at least half of the planetary surface won't support photosynthesis, but for any individual planet it's not a sure thing. The configuration of oceans and continents is a wild card, and as I noted in a previous post, it's possible for a tidally locked planet to have just as much usable land surface as Earth. To elaborate, all you need to achieve that is to have continents cover 60% of the dayside, by no means an impossible configuration. If the continents merge into a supercontinent, the chances are fairly good that the planet will slowly rotate so that it lines up along the sun-planet axis due to gravitational interactions with the asymmetrical mass bulge, and 50% of the time the supercontinent should end up centered on substellar point on the dayside. With more distributed continents, the configuration should be fairly random.

Note that humans can breathe atmospheres with oxygen contents down to roughly one third of the sea level value on Earth, so there's a lot of room to maneuver as far as human habitability is concerned. I would expect a lot of tidally locked planets to be human-habitable, if somewhat on the low side in atmospheric oxygen, if they have a mature biosphere.

 

[Carlobrand]

...I suppose you can argue that tidally locked planets of red dwarf stars might average less oxygen in their atmospheres because at least half of the planetary surface won't support photosynthesis, but for any individual planet it's not a sure thing. ...

It's not that. It's that we're adapted for the current terrestrial environment, not the other way around. There's no real reason to expect to encounter O2 levels aligned with our needs. They might be, or the planet may be dominated by anaerobic local life, or the planet's ecosystem may be balanced at an O2 level well below our needs. There are times in Earth's history where O2 levels may have balanced around the 1 or 2 percent level for hundreds of millions of years, other times when it balanced around 10 percent for hundreds of millions of years.

 

[aramis]

It's not that. It's that we're adapted for the current terrestrial environment, not the other way around. There's no real reason to expect to encounter O2 levels aligned with our needs. They might be, or the planet may be dominated by anaerobic local life, or the planet's ecosystem may be balanced at an O2 level well below our needs. There are times in Earth's history where O2 levels may have balanced around the 1 or 2 percent level for hundreds of millions of years, other times when it balanced around 10 percent for hundreds of millions of years.

And there have been points where it exceeded 25%... enabling dragonflies up to a yard long.

 

[lspitz]

It's not that. It's that we're adapted for the current terrestrial environment, not the other way around. There's no real reason to expect to encounter O2 levels aligned with our needs. They might be, or the planet may be dominated by anaerobic local life, or the planet's ecosystem may be balanced at an O2 level well below our needs. There are times in Earth's history where O2 levels may have balanced around the 1 or 2 percent level for hundreds of millions of years, other times when it balanced around 10 percent for hundreds of millions of years.

That is true enough, but the argument applies to all lifebearing planets. In your earlier post, it sounded like you were making a specific argument regarding the atmospheres of tidally locked planets of red dwarf stars because you seemed to be talking about O2 levels in that context. Sorry if I misunderstood.

Me, I'm still curious to find out whether methane or ammonia atmospheres are plausible in the habitable zone. There's lots of potential problems with accumulating them in a warm, sunny atmosphere because they're easily broken up by UV light, and they may not form a cold trap to keep themselves confined to the troposphere the way that water does. If these sorts of atmospheres are going to work anywhere, they'll work in red dwarf systems where the UV flux is very, very low.

 

[aramis]

That is true enough, but the argument applies to all lifebearing planets. In your earlier post, it sounded like you were making a specific argument regarding the atmospheres of tidally locked planets of red dwarf stars because you seemed to be talking about O2 levels in that context.

Atmospheric O2 levels should be limited to about 0.4 Bar PPO2 by the nature of Oxygen... above that, and it becomes so dangerous that it's raging firestorms... eliminating the sources of free oxygen, which are almost exclusively life. Sufficiently so that, along with Chlorophyl, it showing up on a spectrographic survey will be considered evidence of life.

It's possible for it to be far lower... For example, 0.05 bar would be detectable, and below the 0.15-0.25 bar PPO2 we're comfortable in.

 

[lspitz]

Atmospheric O2 levels should be limited to about 0.4 Bar PPO2 by the nature of Oxygen... above that, and it becomes so dangerous that it's raging firestorms... eliminating the sources of free oxygen, which are almost exclusively life. Sufficiently so that, along with Chlorophyl, it showing up on a spectrographic survey will be considered evidence of life.

It's possible for it to be far lower... For example, 0.05 bar would be detectable, and below the 0.15-0.25 bar PPO2 we're comfortable in.

It's not the absolute oxygen pressure that's the limiting factor for stability against runaway firestorms, but the mixing ratio with other gases like nitrogen, argon and carbon dioxide that act to provide fire suppression. There's a lot of slop in the numbers I've seen quoted by various authors, but there is general agreement that somewhere in the 25 to 40 percent range, oxygen-containing atmospheres become unstable. At least one source I've read states that above 30% oxygen, even thoroughly water-soaked deadfall will burn, and unstoppable wildfires of continental proportions are possible. Other authors cite different percentages. Wherever the true limit lies, once it is reached, the firestorm will convert all available biomass to carbon dioxide, and reduce the level of free oxygen in the atmosphere proportionally in a self-limiting process. 0.4 bar of oxygen would almost certainly be near, at, or above the stability limit in a 1-bar atmosphere, but that would be harmless level of oxygen in a 2-bar atmosphere. A buffer-gas-to-oxygen ratio as low as 3 to 1 appears safe; on Earth, the present ratio is 4 to 1.

There are other complications with high levels of oxygen to consider. If the atmosphere is very dense, absolute oxygen levels can be a problem even when they don't make up more than 25% of the total atmospheric pressure. Oxygen toxicity kicks in a little above 0.5 bars partial pressure for humans; a 3-bar atmosphere of otherwise Earthlike composition (i.e., roughly 21% oxygen, 79% nitrogen and 1% argon) would be toxic to us, even though it would not present a runaway combustion hazard. You wouldn't die immediately, but you couldn't live there for any length of time breathing only the native air.

The final caveat is that humans can't tolerate more than about 3.2 bars of nitrogen before nitrogen narcosis sets in, so there is a limit to how dense a natural breathable atmosphere can be. If you juggle the mixing-ratio requirements for fire suppression vs. the toxicity limits for N2 and O2 and crunch the numbers, the densest plausible natural atmosphere that is breathable without having too much nitrogen or too much oxygen is about 3.7 bars total pressure.