Generating worlds for my campaign

[jwdh71]

Starting a new campaign, essentially from scratch, has been interesting. While I've used the Terran Confederation universe before, it was a long time ago and most of my game notes for it were long gone, as well as most of the systems I generated for it. Since I'm using the T20 system to run the game, I decided to generate the worlds and systems using the T20 rules.

Which has led to some interesting questions. For example, while there are guidelines for placing companion stars, there are no hard and fast rules about it. Does anyone have any suggestions about placing them? How likely are Red Dwarf binary or trinary systems? Are there any known Red Dwarf stars with large numbers of gas giants? (I've generated several M V systems with fairly large numbers of planets and gas giants.) I've also generated several M V systems with fairly extensive planetoid belts (due the the way the size code is generated, 2d6-2 with an additional -2 for being a class M star, plus additional negative DM's for being in close orbits to the star), is this really likely, or would they more likely just have fewer orbiting objects of any kind?

As far as generating the worlds, I have basically been doing a little by dice rolling, a little by GM fiat. For example, when a world atmosphere comes up thin, standard or dense, I have not rolled for the chance for indigenous life, I just wrote it in as a yes, my thinking being that a oxygen-nitrogen atmosphere was next to impossible without SOME sort of biochemical processes going on. Or am I mistaken?

I guess what I am looking for is some feedback from someone more knowledgable about astronomy or planetary sciences than I, so I can see if my assumptions hold any water at all.

 

[Malenfant]

You rang?

I'm not familiar with the T20 worldgen system (I have a copy at home, but wasn't very impressed with it), but I can fact check for you.

Placing companion stars: Companions can be found anywhere from really close to the star (< 1 AU) to thousands of AU. Many companions lie between 1 and 100 AU from the primary star - more distant ones can also be binaries themselves.

There aren't many known M V stars with very large gas giants, but that's not to say they don't exist - we just haven't detected them. I don't think anyone really knows what sort of systems M dwarfs would have, other than that any habitable worlds would automatically be tidelocked to them since they'd be so close to the star. Their systems would probably be smaller in extent than those of more massive stars though.

If O2 is present then there's almost certainly life there. It needs to be replenished by something, else it'd react with rocks and other atmospheric gases - and volcanoes don't pump out O2, so life has to be doing it.

Keep in mind than in reality, the atmospheric pressure is also important in an O2 atmosphere - if the atm pressure is 0.5 atms and its composition is 20% oxygen, then that means that the O2 pressure is only 0.1 atms - which is right at the bottom end of human habitability. O2 pressures that low are only survivable with acclimatisation on Earth, and even then there can be health problems. Or genetic engineering is an alternative, but then the inhabitants would have problems in denser atmospheres.

 

[mad13142000]

In addition to atmosphere, life is also dependant upon water. No water equals no life. (it takes an organic solvent to mix the magic chemicals to make life...and that solvent can't be toxic TO life...water works great). So you have to define a range in EACH of the physical atributes in the UWP...Too small a size would result in a world that either doesn't capture water or air during formation (Mercury) or a world that loses its water due to photodissociation (Mars)...(size...volcanism...you have to have a magnetoshpere to resist the solar winds that will strip a planet of life giving air/water.) So I have to check for size > 3 (or 4)...
Next is Atmosphere...Thin to dense (4 to 9)...taints can be the result of life (too much pollen) or odd gass mixtures (30% argon?) or the result of civilization (hydrocarbons...smog) or odder things...
Any water greater than 0...although I add DMs for larger water numbers (>4)...
I've always used Galactic to generate sectors, and it has the option of generating a Life characteristic...I use the Life number from Galactic and roll 2d6 for the presence of sentient life (18)...I forget the actual rule from Grand Census...
As for systems, I always use Heaven & Earth...
It generates systems based off of CT/MT/TNE extended rules...(Which T20 advises to do in it's small chapter on world generation) Gurps First In may have a more realistic system of generating, but like the rest of Gurps, it is harder and alot wordier...

But basically...
Roll for type of system... Solo, Binary, or Trinary...
Roll for stellar type of each... Type & Size
(this results in acceptable orbits...)
Roll for stellar orbits.
(this leaves orbits for planets, and habitable zones)
Roll for number of planets
(subtracting gas giants and asteroid belts previously rolled...or roll new ones - it depends on how you are generating the system)
Roll for planet placement
Roll for captured planets...satellites...
Roll for physical details for other worlds...

Sometimes you get really lucky and the trinary star rolls for a double itself (oooohhh...quad system)
Traveller systems don't roll for eccentricity, but Gurps does - it affects quite a bit in system generation, but it takes alot of math and dice - all in how much realism you are after...

-MADDog

 

[Malenfant]

It wouldn't necessarily stop at triple system either - we have quads (Capella), quints (Xi Scorpii), and even sextuple systems (Castor) in our local neighbourhood. Though they're not half as common as binaries and trinaries.

 

[jwdh71]

Thanks for the info, it helps that I'm not too far out there in doing the world generation the way I am.

Malenfant: Yes I am very familiar with pressure and the percentage of O2 being important to habitability. I am very careful not to place large populations on planets that don't have breathable atmospheres. The ones that aren't breathable, if they have populations at all, have small mining communities or research stations, depending on the Natural Resource number I roll. If that is low, then it's a barren world. Needless to say I have a lot of empty systems in the subsectors I'm generating...

MADDog: I tried using Heaven & Earth, but I was less than satisfied with the results I got. I would put in UWP info for the world I wanted, and get results that were markedly different. I don't know if I was just using the program wrong, or it was something else, but after several days of messing with it I gave up and am doing the worlds by hand. Slower to be sure, but it's less trouble than redoing the system over and over till the (&^^%&# program gives me something I can use, then having it crash on me before I can save the result.

I've also decided to use something that I'm calling Compatability Factor when dealing with indigenous life, that is, the higher the factor percentage, the more compatable with human biology the native life is. Below 50% and you have to take care not to ingest native organisms, as they are likely to be toxic. Sound reasonable?

 

[mad13142000]

Traveller never got into the compatability issue...
But Gurps did...
They roll 3d6:
3-6 Similar: Disease easily crosses over
7-8 Compatable: Diet needs met; Disease not likely to cross over
9-13 Partially Compatable: Diet supplements needed; Disease will not cross over
14-15 Incompatable: Diet needs not met; Disease not able to cross over and even decay organisms not able to deal with Terran organisms
16-18 Toxic: Organisms have toxic efects upon each other...May equate to a tainted atmosphere

I have one world that I have generated in the Vargr Extents that uses opposite handed molecules from the 'normal' in the rest of the galaxy...The sophonts from there can't live without food from their native planet...I imagine that Terran compatable life is pretty common in 'Charted Space'...Exceptions are very rare...But other regions of the galaxy might be different...It all depends upon which theory (of galactic evolution) you subscribe to...

-MADDog

 

[kaladorn]

If I recall, several games model habitability for planets. The computer models tend to be some sort of exponential or logarithmic response - where a habitability rating of 0.5 of some reference rating will only attract/encourage/create 0.1 times the population of the refence case. That is to say, halving compatibility drops population by a factor of ten. Similarly, going the other way, doubling compatibility makes the planet 10x more interesting to people.

To my mind, I've seen few truly habitable worlds in the TUs spit out by the game system. If you combine:
Temperature ranges (you want a mean round 15-35 C and seasonal variations that stay in the -80 to about +50 range)
Pressures (I'm thinking pressures below about 0.8 standard or above 1.2 would be very bad... maybe even that much deviation from 101.325 KPa isn't good)
Radiation (don't want too much or too little)
and
Gravity (I imagine lower than about 0.7 G is probably bad for long term living, and above 1.1 or 1.2 is going to notably shorten lifespans)

So take these, even before considering food/biology issues, and most planets just aren't going to encourage huge colonizations WITHOUT adaptive genetic engineering.

Seems to me a TU should be full of bioengineered lifeforms, specifically modified to fit their homeworlds. Homo Sapiens Galactus probably has a whole pile of offshoots.

But then most TUs seem to go with the Star Trek-ish "Type M Planet" with standard atmo, grav, atm pressure, temp, etc.

Whereas trying to fudge to one of these using the adv system generation can be... fun.

 

[Fritz_Brown]

thread ressurect!

Traveller systems don't roll for eccentricity, but Gurps does - it affects quite a bit in system generation, but it takes alot of math and dice - all in how much realism you are after...

Actually, World Builder's Handbook does. And, it is then used in all the temperature calculations. (And, yes, there's a lot of math.)

Which brings me to a question, though: shouldn't there be a system eccentricity? I would think the system as a whole would have an eccentricity, then individual planets would vary from that.

Also, should asteroid belts be allowed to have an extreme eccentricity? I would think that would cause the belt to shred away over time. (Higher eccentricity = more collisions = more escapes into inner or outer system)

 

[Higgipedia]

Which brings me to a question, though: shouldn't there be a system eccentricity? I would think the system as a whole would have an eccentricity, then individual planets would vary from that

Well, eccentricity is largely a function of the gravitational force of all the other bodies in the system, so it's really unique to each body orbiting the sun.

Of course, what we are learning is that many of the preconceived notions we had about solar systems is completely wrong.

 

[aramis]

Well, eccentricity is largely a function of the gravitational force of all the other bodies in the system, so it's really unique to each body orbiting the sun.

Of course, what we are learning is that many of the preconceived notions we had about solar systems is completely wrong.

Orbital Eccentricity is a very specific term- it describes how oval the orbit is. 0 is perfectly circular.

There are other orbital issues -

Inclination - how far off from the eccliptic plane the orbital plane is.

Axial Tilt - how far from perpendicular to the plane of the eccliptic a body's rotation axis is

The data we have can't show us axial tilt; inclination may be determined eventually for certain forms of observation.

Eccentricity, however, can be determined by the motion of the star orbited - the effect at aphelion versus perihelion on stellar motion can be used to derive (roughly) the eccentricity. In a perfectly circular orbit, the lobes of the graphed motion will be equal in size and magnitude. In an eccentric orbit, the aphelion lobe will be larger motion but shorter time, and the perihelion lobe will be longer but less. At least one extra-solar has a sufficiently off-symmetric lobe to be noted as having an eccentric orbit.

 

[Fritz_Brown]

So, you're saying that there *wouldn't* be a standard for the system off of which the individual bodies would vary? I can grasp that, though it seems counter-intuitive.

Hmmm... WBH doesn't have anything for inclination. I guess that's a referee TLAR, then.

How about the asteroids? I guess that sort of gets answered by Poolboy - everything affects everything else, so it works out. It *doesn't* answer whether that would tend to keep asteroid belts away from extreme eccentricities, though (above .02?). (I think.)

 

[aramis]

So, you're saying that there *wouldn't* be a standard for the system off of which the individual bodies would vary? I can grasp that, though it seems counter-intuitive.

Hmmm... WBH doesn't have anything for inclination. I guess that's a referee TLAR, then.

How about the asteroids? I guess that sort of gets answered by Poolboy - everything affects everything else, so it works out. It *doesn't* answer whether that would tend to keep asteroid belts away from extreme eccentricities, though (above .02?). (I think.)

That's simple - impact. And no, poolboy doesn't have it right - the influences of anything smaller than a gas giant are trivial. Even gas giants don't work by direct pull, Trojan points not withstanding...

In a belt type situation, high eccentricity objects will tend to collide resulting in displacement out of the belt. As a general rule, everything is orbiting on the same inclination, and in the same direction. Anything that's moving significantly in/out within the belt will tend to hit stuff as it crosses their orbits, and in such cases, both are likely to wind up either ejected or shattered, depending on the details, or if low enough speed, accreting. And, if the displacement is incomplete, it will repeat.

Anything within the gravitational reach of a GG will get pulled a little elliptical as it approaches, and slowed slightly falling back in. But that's pretty stable. Anything in a deeply elliptical orbit, however, have an increased chance of hitting the significant portions of a body's gravity well, and having a significant orbital pattern change, up to and including collision.

 

[Peter Schutze]

>To my mind, I've seen few truly habitable worlds

Several other factors besides those 4 would play a big part in confirming "shirtsleeve" habitability

for rocky bodies, density and day length should roughly determine magnetic field strength which is very useful for brighter or flare stars (which seems to be more common among M's) .... longer days giving lower field strengths

day length and atmospheric pressure relate to wind speed / strength .... earth with a 12 hour day have much more dangerous winds, storms & lightning

the presence of a large moon may help prevent too large an axial tilt but it causes stronger tides and longer days

 

[Fritz_Brown]

OK, on a different note.... How realistic is the base temperature calc in WBH? I'm getting worlds in the Habitable zone that are -226C. Seriously? That doesn't seem to be very habitable to me! I'm also getting some 100C worlds. This is getting frustrating (fewer and fewer worlds make sense, the more I "individualize" them with WBH).

It seems the Orbit Factor and the tables of Inner/Habitable/Outer orbits for each star compound on each other.

 

[Ishmael]

The temperature calc upon which the WBH's temps are based is incorrect. It was originally in Book 6; Scouts, but it is just wrong.

From a post I'd made nearly a year ago,

The term for (1-albedo) should be (1-albedo)^.25, and the 374.025 should be revised to ~286.25 to get the proper ( close enough ) average surface temp for Earth.
This throws off by a fair amount, all of the numbers in WBH's tables.

And even this doesn't do much to make the standard UWP procedure any more realistic or even reasonable.
But to make needed changes ( and everyone likely has their own preferred methods anyways ), the results would not be compatible with the OTU.

My own system is what I posted here;
http://www.travellerrpg.com/CotI/Discuss/showpost.php?p=403590&postcount=36
But its really only valid for worlds in the habitable zone.
The inner, middle and outer zones have different values/procedures due to the lack of wtaer aiding a carbon cycle in for the atmosphere.

This site has a section that explains that in terms of comparing Venus-Earth-Mars
and is very nice for worldbuilding in general.
http://www.astronomynotes.com/solarsys/s1.htm