Gas Giant Migration in GURPS SPACE

[hal]

Hello Folks,
Question - if a gas giant is migrating from outside the snow line towards the inner system, would it by necessity, also destroy any planetary formation in those orbits that the gas giant has to cross? This assumes that the gas giant is migrating during the early formative years of the star system


As it migrates inwards, wouldn't it disrupt the orbits of any planets within the system to the point where they would no longer be there? This assumes that the migration occurs after the birth and after the planets have started to form or have formed.

[Anthony]

Originally Posted by hal

Hello Folks,
Question - if a gas giant is migrating from outside the snow line towards the inner system, would it by necessity, also destroy any planetary formation in those orbits that the gas giant has to cross?

Everything in the orbits it crosses is going to have gravitational interactions with the gas giant. Mostly that means ejected, though captured is a possibility. However, it's possible for planets to form after the gas giant passes through.

[David Johnston2]

Originally Posted by hal

Hello Folks,
Question - if a gas giant is migrating from outside the snow line towards the inner system, would it by necessity, also destroy any planetary formation in those orbits that the gas giant has to cross? This assumes that the gas giant is migrating during the early formative years of the star system


As it migrates inwards, wouldn't it disrupt the orbits of any planets within the system to the point where they would no longer be there? This assumes that the migration occurs after the birth and after the planets have started to form or have formed.

No. I mean it certainly could but it also might just increase the eccentricity of the orbits. A migrating gas giant isn't even necessarily in the same plane of rotation as the rocky planets.

[hal]

Thanks guys.

I was trying to decide whether or not to include the option for migrating gas giants for system generation rules for Traveller star systems. If there are supposed to be main worlds in a star system with a migrating gas giant, but migrating gas giants inflict chaos in the other orbits - that defeats the purpose of expanding the generation of a star system from its "main world" to that provided by GURPS SPACE or GURPS TRAVELLER: FIRST IN (although First In doesn't have that feature).

Right now, I'm experimenting with VB.NET to see how much I can automate the data generation of star systems and how much I would be better served to generate manually. If it takes me months to get the application written, then the return on investment (time) isn't worth the effort if I can detail the star systems within less time than it took to write the code. Frankly, I don't want to have to detail 439 star systems by hand (and I could just do a subsector and be done with it to be sure!!!).

Time will tell. But this answer helps, so thank you Gentlemen.

My main purpose for generating the data is to see just what effect it may have on ship travel from star system to star system. For instance, what would be involved in smuggling? Could a ship for example, knowing where a planet will be in its orbit - jump to directly opposite of where the planet is, so that any Jump Flash is lost in the star's emissions? Could a smuggler drop off goods by placing it in orbit with an IFF communicator, then let the people who have to pick up the shipment, know the orbit specifics, and let them go pick it up in say, a "Boat"? If the boat is local, could such a smuggling operation have a good expectation of not being caught unless the port authority checks ALL craft - even if the craft are going to local ports instead of the interstellar port?

What I want to do is turn a star system into a "Character" so that player characters have something specific to interact with. A class V starport is probably not going to be vulnerable to such tactics. On the other hand, a class III starport might. Something stolen from a star system 3 parsecs away, could be sent to space via a boat, be left in deep space with the coordinates made available to the pick up ship. Said shipment then could be pulled on board and the ship refuel via wilderness refueling at a local gas giant, and then head to yet another location.

In all, I would like to be able to examine all of the possibilities with a fully detailed set of star systems.

[David Johnston2]

It's worth bearing in mind that thanks to the Ancients the Traveller universe has a lot of still terraformed planets. Thus there's a reason why there are Small worlds with breathable atmospheres here and there.

[hal]

Originally Posted by David Johnston2

It's worth bearing in mind that thanks to the Ancients the Traveller universe has a lot of still terraformed planets. Thus there's a reason why there are Small worlds with breathable atmospheres here and there.

That dodge is tiresome when you consider that there are too many of them.

There are other reasons I am looking to redo the entire thing using GURPS SPACE or GURPS FIRST IN - but explaining why would come across as product bashing.

TO put it succinctly...

(taken from a post on another forum I made earlier...)

CT: SCOUTS mandated that if you had a world with an atmosphere type 4-9 OR Population 8 for main world, the 2d6 roll for the primary star type was supposed to be at +4. If you look at Megatraveller's rules for generation primary stars of any pregenerated world (which all of the Spinward Marches were by dint of being published as supplement 3 by the way), you would find that the rule is the same: roll 2d6 and add a +3 modifier.

Of those systems in Spinward Marches, there are 439 star systems. Of those, only 264 meet the requirement that the planet has an atmosphere 4 to 9. In addition, there were also another 25 that met the criteria of population 8+ but not the atmosphere type. That's a total of 289 star systems that should have had a +4 modifier on the 2d6 roll for star type. That means, that the minimum roll would have been a 6 and the maximum would have been a 16 on 2d6.

When you look at the statistical results - you'll find that only 8% of the star systems that meet the criteria of atmosphere 4 to 9, or population 8+ should have an M spectral class star. The spectral class A should not even be possible, as you need to roll a 2 on 2d6 unmodified. The modified roll of 2d6+4 should make a roll of a 2 impossible. Yet, the new survey has 29% of all those stars as being M class spectral types. Per the rules given in either Scout or MegaTraveller's Referee book, the bulk of the stars should have been K class. Instead, the breakdown is as follows:

M: 85
K: 65
G: 69
A: 1
F: 69

Clearly, when someone wrote the program to spit out the results for the Spinward Marches data, they sort of didn't follow the rules as given.

In addition, there are a lot of worlds that have a diameter that is too small to even retain water vapor - let alone water, which is why some of the worlds need some serious tweaking in order to have them make more sense. When I used to hang around Citizens of the Imperium - there was a discussion on why some of the worlds data were different than the canon values, for much along those lines.

Me? I'm awfully tempted to go back to the original data, use GURPS SPACE to generate the actual stellar data for the star system, and leave it at that - my own "In my traveller universe" instead of using the stellar data from the other stuff.

That's just me however, and generating 439 star systems by hand is a royal pain in the arse - writing the code would require that I actively sit down and code, which these days, I lack the determination to see to the end. :(

Then again, T5 had good advice: MOAN - Map only as Necessary. That also means "Generate full data only as necessary."

(end of material taken from a post on another forum I made earlier...)

That was the post I made some few weeks back. Now, I'm actively coding to see how much I can automate of the process so that I can simply do the other stuff manually (if anything at all). I've currently gotten to where I'm now using Jon's new rules for multiple star system generation, along with primary star generation (you can find it on his webpage).

So now, I can generate the worlds stat up to step 6. I'm close to starting on step 7 for the Resources and Habitability values. Once that is done, the next step will be to populate the star system with gas giants and other worlds or empty orbits. That is why I asked about the Gas Giant Migration, thinking that in terms of Traveller, if a star system has a main world generated for it, and a migrating gas giant destroys worlds etc - then I have to exclude it from the coding. Instead, I'll be including it. :)

Imagine how much fun it would be to find out that a migrating gas giant is in near orbit to a habitable world - much like Venus is close to Earth (for instance).

[Nemoricus]

GURPS Space's treatment of gas giant migration is something of an after-the-fact view. If there was migration, then there's gas giants in an eccentric or epistellar configuration. If there was no migration, then they're in conventional orbits.

GURPS Space also gives no consideration whatsoever to the stability of the orbits it spits out, so if you care about that, you'll have to check the results yourself.

That said, if there's a main world in the system, then for consistency its orbit should be treated as the most important one. Conflicts are resolved in favor of the main world. If this results in the first gas giant being displaced from what it would be without such a world, then so be it.

[AlexanderHowl]

From our observations of exoplanets, there are a lot more stable orbits than people initially thought. Look at Kepler-90, which has 8 planets, including two Jupiter mass planets, within 1 AU of a G0V star. The system is two billion years old, so it is stable, but the orbital separations make no sense if you use any of the established orbital models. It seems like every time we think that we have figured out exoplanets, we discover a new system or a new exoplanet that throws every previous theory into the woodchipper.

[hal]

Originally Posted by Nemoricus

GURPS Space's treatment of gas giant migration is something of an after-the-fact view. If there was migration, then there's gas giants in an eccentric or epistellar configuration. If there was no migration, then they're in conventional orbits.

GURPS Space also gives no consideration whatsoever to the stability of the orbits it spits out, so if you care about that, you'll have to check the results yourself.

That said, if there's a main world in the system, then for consistency its orbit should be treated as the most important one. Conflicts are resolved in favor of the main world. If this results in the first gas giant being displaced from what it would be without such a world, then so be it.

The methodology seems to be to first place the gas giant within the star system. Then place the main world somewhere that is mathematically consistent with the specifications generated for the main world absent any real stellar data. The location it should be placed is a mathematical formula.

After that, then check for all remaining orbits to determine what goes where, and if two worlds are close by that they violate the possible distance that can be rolled on the table (ie ratio between current orbit and next) - then there may be some juggling required.

In all? I'd rather randomly generate the data, and if something fails to be possible per the standards, flag that generation as faulty, and then perhaps either randomly generate a new system, or do it by hand, or fix the faulty one by hand.

[hal]

Originally Posted by AlexanderHowl

From our observations of exoplanets, there are a lot more stable orbits than people initially thought. Look at Kepler-90, which has 8 planets, including two Jupiter mass planets, within 1 AU of a G0V star. The system is two billion years old, so it is stable, but the orbital separations make no sense if you use any of the established orbital models. It seems like every time we think that we have figured out exoplanets, we discover a new system or a new exoplanet that throws every previous theory into the woodchipper.

Just a thought...

The distance in light years between us and the star in question, means that we're looking at data that is already old. Then you have to ask yourself this...

Are they currently really stable, or are they still in the process of being consumed by the star itself, we're just not long lived enough to know that this is in fact, happening.