Steve Jackson Games Forums - [SPACE 4e] System Design help? (star systems that is...)

Steve Jackson Games Forums (https://forums.sjgames.com/index.php)

- GURPS (https://forums.sjgames.com/forumdisplay.php?f=13)

- - [SPACE 4e] System Design help? (star systems that is...) (https://forums.sjgames.com/showthread.php?t=15349)

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

For the double planet, I prefer doing one bigger, usually about 0.2-0.4G bigger, this makes the sattelite "planet" almost a moon, except the two planets actually both orbit around a center of mass which then orbits around the star, so only one orbit around the star is taken up.

The two planets are likely tidally locked to each other and at least 1-2 million miles apart, but there's no reason they wouldn't rotate around their center of mass in a stable orbit, while the center of mass orbits the sun.

This then allows you to have the third planet in the life zone some 100 million miles or so away from the center of mass of the double planet.

For other effects on the system, just consider the total mass of the two planets as if it were one larger planet in the center of mass orbit.

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

Quote:

Originally Posted by Ze'Manel Cunha

The two planets are likely tidally locked to each other and at least 1-2 million miles apart, but there's no reason they wouldn't rotate around their center of mass in a stable orbit, while the center of mass orbits the sun.

The Moon orbits the Earth at 30 Earth-diameters. You're talking about something that's in the range of 100- to 200+ Main-Planet-diameters. Is there a reason you chose that distance? I'm guessing the effects on tidal force. So we're not talking about a Rocheworld, are we? That is, two planets close enough together that they bulge towards each other?

Going back to life-zone gas giants, how do I generate heating effects for major moons of gas giants? I've got a gas giant that's generating (through, again, some fudgery) a Standard Ice moon. I'd like to find out how to get that extra black-body temp to push it into a warmer temperature, and thus manage to get a Standard Garden possibly further out in the life-zone.

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

Quote:

Originally Posted by Pragmatic

I would think that tidal effects of two planets tide locked together wouldn't be that bad, actually. The main reason the tidal effects of the moon are so noticable is because they act differently upon different areas of the earth's surface at different times. With two tide locked worlds they will reach a point of equilibrium in which the tidal effects should't cause problems anymore.

Quote:

Originally Posted by Pragmatic

So we're not talking about a Rocheworld, are we? That is, two planets close enough together that they bulge towards each other?

Any two bodies orbiting around each other will bulge towards the other; that's the nature of gravity pulling on them. The Earth's surface bulges slightly towards the moon in it's orbit, however the bulge is relatively small. Of course, the bulge of the liquid oceans with the moons orbit is much more noticible to us on Earth. The closer together the two bodies are the more noticible the bulge will be. On tide locked worlds the bulge will be in one place, and thus will be more noticible still.

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

Quote:

Originally Posted by Pragmatic

Going back to life-zone gas giants, how do I generate heating effects for major moons of gas giants? I've got a gas giant that's generating (through, again, some fudgery) a Standard Ice moon. I'd like to find out how to get that extra black-body temp to push it into a warmer temperature, and thus manage to get a Standard Garden possibly further out in the life-zone.

a) Forget for regular Gas Giants.
b) Brown Dwarfs have Luminosity. We discussed this long ago on the Delphi board, and IIRC Constantine said that for multiple heat sources one should add all (L/R^²) for the individual sources before drawing the fourth root from the sum and multiplying with 278.

Three life-zone Garden planets IS possible.

I hope this doesn't screw up the formatting. The first column is Hydrographic percentage. For Garden worlds, there are three ranges: 21-50% (represented by 050), 51-90% (represented by 070), and 91-100% (represented by 100). The second column is Atmospheric mass, which ranges from 0.5 to 1.5 (or, if rolled randomly, 0.3 to 1.8), but 0.7 to 1.3 will cover most situations. Then across the top of the data is the mid-range of Cold, Chilly, Cool, Normal, Warm, Tropical, and Hot climate ranges.

Code:

Hydro        AtmMass        261        272        284        295        306        317        328

050        0.7        1.187        1.093        1.003        0.929        0.864        0.805        0.752

050        0.8        1.222        1.125        1.032        0.956        0.889        0.828        0.774

050        0.9        1.257        1.157        1.061        0.984        0.914        0.852        0.796

050        1.0        1.292        1.190        1.091        1.011        0.940        0.876        0.818

050        1.1        1.328        1.223        1.122        1.040        0.966        0.90        0.841

050        1.2        1.364        1.256        1.152        1.068        0.993        0.925        0.864

050        1.3        1.401        1.290        1.183        1.097        1.019        0.950        0.887

070        0.7        1.086        1.000        0.918        0.850        0.790        0.736        0.688

070        0.8        1.118        1.029        0.944        0.875        0.813        0.758        0.708

070        0.9        1.150        1.059        0.971        0.900        0.836        0.779        0.728

070        1.0        1.182        1.089        0.998        0.925        0.860        0.801        0.749

070        1.1        1.215        1.119        1.026        0.951        0.884        0.824        0.769

070        1.2        1.248        1.149        1.054        0.977        0.908        0.846        0.790

070        1.3        1.282        1.180        1.083        1.004        0.933        0.869        0.812

100        0.7        0.990        0.911        0.836        0.775        0.720        0.671        0.627

100        0.8        1.019        0.938        0.860        0.797        0.741        0.690        0.645

100        0.9        1.048        0.965        0.885        0.820        0.762        0.710        0.663

100        1.0        1.077        0.992        0.910        0.843        0.784        0.730        0.682

100        1.1        1.107        1.019        0.935        0.867        0.805        0.750        0.701

100        1.2        1.137        1.047        0.961        0.890        0.827        0.771        0.720

100        1.3        1.168        1.076        0.987        0.914        0.850        0.792        0.740

By playing with hydrographic percentage and atmospheric mass, it's possible to get three life-zone planets without having to resort to double-worlds, life-zone gas giants, or brown dwarfs.

The numbers above are multiplied by the SQRT of luminosity to get the orbital radius.

I have to get ready for work, so I haven't tested these numbers through the world creation system. I don't know what the atmospheric pressures will turn out to be, for instance. I was only trying to get average world temps within specified ranges. By varying atmMass, you should be able to adjust the temperature to suit, while keeping the atmospheric pressure under control.

Edit: Took out example, which wasn't accurate. Went back and checked the numbers. The following constraints apply: No multiplier greater than 1.342 (blackbody temp = 240K) and no multiplier less than 0.755 (blackbody temp = 320K). So it looks like you can't get three life-zone planets without resorting to doubles or gas-giant moons. The third planet will always end up a Greenhouse or an Ice planet.

Dang it. :(

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

Pragmatic,
Thank you for trying...and that chart.

Okay lets say I can get TWO of my desired planets within the standard lifezone.
The Third planet is actually a "moon" orbiting the Gas Giant closest to the "LifeZone" . Does that make any sense??

Could that Moon/Planet have enough properties to sustain human life if it got enough light from both the local star and the Gas Giant? Would a Gas Giant rafdiate or reflect enough warmth? (thinking harsh mostly-livable Desert Planet.) Imagine said planet to be halfway between Earth and Mawrs in living quality - with possible terraforming assistance/modification sometime in its recent past - less than 300 years ago.

- Ed Charlton

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

You can't get a gas giant in the life zone if you have two terrestrial planets in the life zone, and the gas giant not in the life zone won't add enough heat to make a world orbiting it habitable. Assuming you don't want a binary system, I'd go with the trojan point suggestion from page 1 -- you have a gas giant in the life zone, with a terrestrial planet its 4th and 5th trojan points, and another terrestrial planet orbiting the GG. This is grossly unlikely but not forbidden by orbital mechanics.

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

Thanks "A" , thats pretty helpful.

My players may not make it to that Star System for a while still.

But at least you have pointed me in the right direction.

The planet with the "desert-like" environment should be mostly like either Israel or Lebanon in the general climate and terrain of the livable areas. My player was also wanting that one to be the furthest out from the system's star ...or at least the first planet that incoming Travelers have a chance of landing on.

- Ed Charlton