[SPACE 4e] System Design help? (star systems that is...)

[Qoltar]

Alright I bought GURPS:SPACE 4/e and I am looking for a little bit of advice or at least someone to point me in the right direction.

For a player in my campaign I need to concoct a star system that has THREE planets within the life zone. Thats right 3 (!!) planets in some kind of tolerable and believable orbit bands and such ...all of them plausibly habitable for humans. And is VERY "okay" if one of the 3 turns out to be a mostly "Desert World" . I also own INTERSTELLER WARS ....but I figure might as well use the more detailed system.

Any advice on this? Should I just roll dice until I get "close" to what we want? Has someone already got parameters close to this in a Playtest exercise? (and please don't send me a link to a PYRAMID article - am not a subscriber....can't afford it ..YET)

So, any planetary system designing versions of "Gearheads" out there...That can give me some tips or suggestions?

- Edmund W. Charlton

[t@nya]

I don't have GURPs Space yet, but I am interested in astronomy in a general way (read books and articles). I suggest that you roll up a system and then adjust it so that three planets are habitable. For example, Mars might very well be habitable today if the planet had greater mass and hence gravity. This would have allowed it to hold on to more of it's original atmosphere. Venus would have much more habitable (though very hot, perhaps too hot for humans) in the early history of the solar system (it started out with water which, ironically, made the greenhouse effect it suffered later that much worse). In the outer solar system, a large enough gas giant could possibly warm it's moon enough for human inhabitation to be possible (maybe a ocean world similar, but warmer, than Europa).

[MrId]

It should be possible, especially if you wave your hands real hard. Mumbling something about terraforming will help a lot too, if that fits your conception of the system. I tried to run some numbers, but couldn't quite get it, but I got pretty close. You'll end up with one hot world, one "goldilocks" world, and one that's actually a Standard(Ice) type rather than Standard(Ocean), but it's really close.

With the Basic Worldbuilding chapter, you can generate as many habitable planets as you want and put them wherever you want, so I assume you're asking about the Advanced Worldbuilding chapter. One problem that may develop is that you'll need a fairly bright star -- I'd go something like an F6 V, although you could probably get away with a G class star. This is only a problem if you want the planet to have native life, as bright stars will have shorter lifespans, and any aliens won't have long to evolve.

I would not roll dice until you get close, because you'll be rolling dice for a long time. I'd just use the rules to guide your decisions.

Let's just start with an F6 luminosity, main sequence star, on page 103. We'll also assume it's a single star, although you can add a distant companion later if you really want. Set the age to something you like (or roll dice), but it should not go over the main sequence age. For arguments sake, I'll go with 2.3 billion years for age. With an F5V star, this gives a luminosity of 3.2. The orbital zones (p. 106) are going to be: Inner Limit = .13 AU, Outer Limit = 52 AU, and a Snow Line Distance of ~8.67 AU. So your three garden planets will be within 8.6 AU of the star, and probably quite a bit closer.

Generating gas giants next, if you want three habitable planets, you'll probably want either no gas giants or a conventional gas giant arrangement. I'd go with gas giants in the conventional arrangement, but it really doesn't matter for the most part.

Now this is the tricky part -- setting up orbits to give three planets in the Standard or Large Garden Range (241-320 Kelvin). Using the formula on p. 108, we see that a temperature of 241 Kelvin give us an orbital radius of 2.3 AU, while 320 gives us a radius of 1.3 AU. Now it's possible for us to get one planet at 1.3 AU, one at 1.82 AU, and one at 2.5 AU, given the minimum ratio between orbits of 1.4. The other orbits aren't important for the moment, so we can generate those later. We'll put a standard planet in each of the three orbits, and do moons later.

What's really important is the blackbody temperature. For our luminosity (3.2) we get blackbody temperatures of 320 Kelvin at 1.35 AU, 275 Kelvin at 1.82 AU, and 235 Kelvin at 2.5 AU. Your outermost planet is technically a standard (Ice) planet in the inner most one will be uncomfortable in the summer, but it's pretty dang close. You can work out the rest of the details to fit your own setting, or fiddle with it to get it close to what you want.

Hope that helps.

[Qoltar]

Id,

That Is VERY helpful .
Funny thing is ..I used to be better at this number-crunching stuff when I was a teenager ......nowadays my brain starts rebelling and just wants to do characters and plots.

Anyone else have advice about this ? Who knows - this might help out some other GURPS GM or player out there.

- E.W. Charlton

[MrId]

Originally Posted by Qoltar

Id,

That Is VERY helpful .
Funny thing is ..I used to be better at this number-crunching stuff when I was a teenager ......nowadays my brain starts rebelling and just wants to do characters and plots.

Anyone else have advice about this ? Who knows - this might help out some other GURPS GM or player out there.

No problem. It was kinda fun to fiddle with the design constraints to make a specific system. Usually I just go by the dice rolls and work from the "dirt up" rather than from the "story down".

The three planets will all be fairly different, and I think you should be able to easily fudge the outermost one into an Earthlike world that's perpetually glaciated, but has enough photosynthetic life to create a marginal, but breathable atmosphere (a thick atmosphere will help warm it, too.)

Personally, I want to see how the system turns out once you get it the way you like it.

[Blood Legend]

that Inner planet, 'Hot in the summer.' Easy solution, give it an almost spherical orbit, same temperature all year round, probably like a semi-tropical rainforest or something like that. outer planet, thick atmosphere. Done and done.

I'm not much of a number cruncher, don't have the books, and definitly don't know my astronomy so scuse any blatant stupidity.

[abatishko]

Originally Posted by Blood Legend

that Inner planet, 'Hot in the summer.' Easy solution, give it an almost spherical orbit, same temperature all year round, probably like a semi-tropical rainforest or something like that. outer planet, thick atmosphere. Done and done.

Unfortunately, that's not what causes summers to be warmer than winters. Witness the fact that our world has summers at opposite times of the year depending on whether you are in the northern or southern hemisphere. This would be impossible if it was caused by proximity to the sun, because you can be closest to the sun at two times during the year no matter what your orbit looks like.

However... he's got the right concept. Give your innermost planet an axial tilt of 0. Then you won't have any seasonal effects. Technically this only shifts the problem from a seasonal one to a latitude one. The equator would be too hot. But, the temperate and polar zones might just be ok.

[copeab]

Originally Posted by Qoltar

For a player in my campaign I need to concoct a star system that has THREE planets within the life zone. Thats right 3!! planets in some kind of tolerable and believable orbit bands and such ...all of them plausibly habitable for humans. And is VERYT "okay" if one of the 3 turns out to be a mostly "Desert World" . I also own INTERSTELLER WARS ....but I figure might as well use the more detailed system.

I'd go for three very large moons around a very large gas giant that's in the habitable zone.

[Ze'Manel Cunha]

Originally Posted by copeab

I'd go for three very large moons around a very large gas giant that's in the habitable zone.

I've used that model, it's a valid idea, and its unlikeliness can be waved off with enough possibilities.


The other model I've used, though possibly even less likely, is a double planet* along with a third planet within the habitable zone.



*The double planet setup simply requires the equivalent of an Earth-Moon system on a greater scale, the planets would be further apart, but the tides would still be greater than ours.

[Qoltar]

Holy *BLEEP*!,
The Author of the book himself replied. Wow!! Well, I will have to give your advice and suggestion a little more weight.

Looks like time to get out out the notepaper pad, a few pens and work all this out. I'm meeting with the player in question this Saturday afternoon.
If anyone has any more suggestions - I will look forward to reading them.

- Edmund W. Charlton