GURPS SPACE and placing orbits

[hal]

Hello folks,
I'm just curious...

Why does GURPS SPACE suggest placing the gas giant orbit first, and then, placing the main world orbit second? It advises in the body of material, that a GM resolve any conflicts where the gas giant and the main world are too close - to either regenerate the star system information - or to move the Gas Giant.

Wouldn't it make more sense to place the Main World first, then place the Gas Giant and other planets subsequent to the Main World?

In addition, if GURPS SPACE permits the idea that gas giants can be anywhere within the star system - then why not simply place the main world first, and work inwards and then outwards of the star system in the placement of the system planets? If the system is supposed to be a "traditional' Gas giants are outside the snow line - then simply make it so that any gas giants generated inside the snow line automatically are planetary objects, and if gas giants are permitted inside the snow line, leave the gas giant generated as is. Any gas giants generated outside the snow line are of course, desirable.

Just musing aloud...

[AlexanderHowl]

In light of the exoplanet discoveries over the last decade, the GURPS rules for creating star systems does not make much sense. Orbits can occur closer in real life than they can occur in GURPS, with some exoplanets having such close orbits that they pass within 0.01 AU of each other. In addition, we have planets that are impossible to design in GURPS, such as a world with over four times the density of the Earth (KELT-1 b) or with a world with a surface temperature of 7,000 K (Kepler-70b). In addition, when you look at our solar system, Jupiter and Saturn possess many more moonlets than are possible under the GURPS system.

[Nemoricus]

Originally Posted by hal

Wouldn't it make more sense to place the Main World first, then place the Gas Giant and other planets subsequent to the Main World?

It would. Why GURPS Space doesn't do this, I don't know. But, it's a fairly small change to come up with the orbit for the main world first and then place the first gas giant, if any.

then simply make it so that any gas giants generated inside the snow line automatically are planetary objects.

GURPS Space already accounts for this. If the system has the Conventional Gas Giant arrangement, then you don't roll for gas giants inside the snow line. See the Gas Giant Placement Table on page 110 of GURPS Space.

[hal]

Originally Posted by Nemoricus

It would. Why GURPS Space doesn't do this, I don't know. But, it's a fairly small change to come up with the orbit for the main world first and then place the first gas giant, if any.



GURPS Space already accounts for this. If the system has the Conventional Gas Giant arrangement, then you don't roll for gas giants inside the snow line. See the Gas Giant Placement Table on page 110 of GURPS Space.

That's why I mentioned it. The primary difference between a standard system and one that allows gas giants inside the inner limit is just that.

All I need to have is "If ConventionalGasGiant Then" and the code writes itself (so to speak). ConventialGasGiant would be Boolean...

At this stage, I have the ability to generate the stats on the stars, its companions (if any) as well as everything related to the main world. I will finish up on the loop I need for configuring orbit values. It will be a "do until" with a test to see if the limits are within the max possible orbit multiple from step 22. If within that limit, then I stop.

Once the orbit values are calculated, then all that remains is to populate the orbits with a world (or not).

After that, I'll work on the rules for binary stars and forbidden zones. The reason for that is - I will make the application such that it can open an excel spreadsheet, read in the data line by line, and get star name and hex ID value in addition to the Universal World Profile.

Since every star in Traveller has a main world - that implies that the values for "forbidden zones" can not include the life zones by default.

So, I need to set the thing up so that I can read in a value, view it, generate the star system - if it looks good, save it to either a text file or an excel tab/sheet and go from there.

Now comes the issue of what happens when you have a "Garden World" in Traveller but only has 10% surface area of water...

;)

[David Johnston2]

Originally Posted by hal

Since every star in Traveller has a main world - that implies that the values for "forbidden zones" can not include the life zones by default.

Only if the main world has a non-exotic atmophere. Although personally I'm done with forbidden zones. They seem like an out of date concept.

[Nemoricus]

Originally Posted by David Johnston2

Only if the main world has a non-exotic atmophere. Although personally I'm done with forbidden zones. They seem like an out of date concept.

GURPS Space uses forbidden zones to represent regions where the orbits would be unstable due to the gravitational effects of the other star. Are there examples of known planets orbiting in these regions?

[tshiggins]

Originally Posted by hal

(SNIP)

Now comes the issue of what happens when you have a "Garden World" in Traveller but only has 10% surface area of water...

;)

Well, that's open water, right? You could have the rest of the water locked up in ice-packs, or something, or have a planet with only open water at the poles and the rest sucked into a hot atmosphere as water vapor due to recent climactic changes.

Basically, run with the 2300AD definition of a "garden world" -- anything that has even a small biome and an environment where humans can live with minimal life support.

It doesn't have to be a huge area (Plateau, in Niven's Known Space or Crater, in 2300 AD), and it doesn't have to be easy, it just has to be possible.

I mean, this is mostly used for science fiction campaigns, and we've learned planetary development can be stranger than we ever thought possible, so I'd just roll with it.

[AlexanderHowl]

Originally Posted by Nemoricus

GURPS Space uses forbidden zones to represent regions where the orbits would be unstable due to the gravitational effects of the other star. Are there examples of known planets orbiting in these regions?

Yes, half of the known exoplanets are found within forbidden zones.

[Nemoricus]

Originally Posted by AlexanderHowl

Yes, half of the known exoplanets are found within forbidden zones.

Can you provide specific examples?

[AlexanderHowl]

Originally Posted by Nemoricus

Can you provide specific examples?

The Kepler-42 system. Kepler-42c orbits at 0.006 AU, which is less than half the 0.013 AU inner limit of a star of 0.13 Sol-masses. Kepler-42b orbits at 0.0116 AU, which is also within the 0.013 AU inner limit of a star of 0.13 Sol-masses and within the 0.15 AU exclusion zone of another planet. Kelper-42d orbits at 0.015 AU, which is also within the 0.15 AU exclusion zone of another planet.

If you are talking about the forbidden zone due to the gravitational influences of another star rather than the primary star or another planet though, that is a bit harder, as we have so few examples because binary systems play havoc on our detection methods. Kepler-16b is probably the best example, as the binary star has an eccentricity of .2 with an average separation of 0.22 AU, meaning that the maximum separation of 0.264 AU would place the average orbital separation of Kelper-16b within the forbidden zone of three times the orbital separation for a circumbinary orbit. The planet has an orbital separation of 0.7 AU with very low eccentricity, which is within the forbidden zone of 0.852 AU of the binary star that it orbits.