The Lair of Evil Dr Ganymede

2300AD Celestia output!

I’ve been tinkering around a little bit more with my 2300AD worldgen script – I was actually adding the capability to generate Celestia versions of the systems that the program creates (as you can see from the screenshot above, I was successful!), but while I was at it I figured I’d make a few tweaks to some parts of the the system that I wasn’t too happy with. I think the results are much better now.

World Density: First I added a new rocky core density category so that worlds between 4000 and 7000km radius had densities between 0.75 and 1.00 Earths – previously they could go down to 0.5 Earths and I was ending up with habitable planets with unrealistically low densities for their size as a result. Worlds smaller than 4000km radius still have densities between 0.5 and 1.00 Earths, and worlds over 7000km radius have densities between 0.8 and 1.3 Earths as before.

Icy Core size: I wasn’t happy with the Icy Core size either – I was getting a lot of Titanian and Iceball worlds with the first realistic system and that didn’t make much sense to me – in the outer zone it should be easier to accrete material and you’d be much more likely to end up with gas giants instead of Titan and Pluto-like bodies. “Iceballs” don’t really make much sense to have as planets either – they’re really just the equivalent of Dwarf Planets, which would be found in a Kuiper Belt (which is usually assumed to be present but not mentioned). So now Icy Core radii range linearly from 3d6 to 8d6 times 500km, instead of starting at 1d6 – this means we end up with larger icy bodies, and a greater chance of gas giants (though there are still a small number of iceballs created, mostly below 3000km radius).

Snowballing: One limit from the original system was that ‘snowballing’ into a gas giant couldn’t happen within the Inner Zone if the MMW was greater than 2. This seemed a bit arbitrary to me, so I removed that limitation to allow it to occur at any planet where the MMW is greather than 2. As it turned out, changing it didn’t actually seem to make any significant difference to the output! Presumably this is because it’s very hard to get an inner zone planet that would be massive enough to have an MMW over 2 in those conditions.

Gas Giants: I’ve now subdivided Gas Giants into new World Types based on their sizes. Failed Cores are still under 12000 km radius. Small Gas Giants are between 12000 and 40000 km radius (this includes Uranus and Neptune). Gas Giants are larger Jovians that are larger than 40000 km radius but less than 2 Jupiter Masses (2 MJ) – this includes Jupiter and Saturn. Superjovians are over 40000 km radius but have masses between 2 and 13 MJ. Finally Brown Dwarfs are jovians that have masses over 13 MJ. This adds a bit of variety to the systems generated (and lets me use different textures in the Celestia output!)

I also changed how these gas giants are created. I still stick with the ‘snowballing’ idea, but something that always bugged me about that was the fact that the the original core density is assumed to be the density of the resulting gas giant, which can’t be right since all that extra hydrogen and helium has a much lower density than the icy/rocky core and would reduce the density of the resulting jovian. Now, if a planet snowballs into a Gas Giant then its density is re-rolled on a new density table depending on its final radius – this allows Superjovians to be 2-12 Jupiter masses, and Brown Dwarfs to be between 15 and 65 Jupiter Masses. It’s not the prettiest system since values are rolled and then rerolled, but it seems to get the right kind of results.

Garden Worlds: I realised that the lowest mass F V star has a total main sequence lifespan of 4 billion years, which means that garden worlds aren’t really likely around them. So while Pre-Garden, Post-Garden, or Frozen worlds are an option in their habitable zones, Garden worlds and Glaciers (which are just Garden worlds in a temporary ice age) are now no longer possible there.
Continue reading ‘[2300AD] The GDW 2300AD Worldbuilding system: Part 3 – Final version!’

Gas Giant orbiting a star in a triple G V system (image created in Space Engine)

Now that I’ve got the Realistic Near Star Map Project out of the way I thought I’d take a look at the world generation system from the original GDW 2300AD Directors Guide, which I haven’t really examined in detail before. To do this, I automated the generation system so that I could generate thousands of systems and go over the statistics of the results.

However, I had to make a few tweaks to the system while writing the program so it’s not entirely faithful to the original system in the Directors Guide. First, the 2300AD system was designed to be used with existing stars, so I had to add a stellar generation system to generate those on the fly. I used a slightly modified version of my Revised Stellar Generation Tables (the original is available on my Worldbuilding page), that only generated solo stars (largely because it was easier to program that way). I used the stellar data tables from 2300AD to determine the stars’ luminosity and radius, but I just used the mass from the “V” column since in reality stars don’t change their masses significantly when they evolve into sizes II, III and IV. I also assumed fixed masses for the II and III Giants (1.5 Ms) and the White Dwarfs (0.5 Ms).

Another issue was that 2300AD is missing an Orbital Zone – there is a gap between the outer edge of the Habitable Zone and the inner edge of the Outer Zone. This “Middle Zone” is where Mars is located in our own Solar System, and cold rocky bodies (as opposed to icy bodies) would dominate there.

Additionally, in the original system, Gas Giants could snowball to immense sizes – the radius multiplier could go up to 16x the original rolled radius, which meant that you could potentially get Gas Giants with a radius of up to 384,000 km – over half the size of Sol! Obviously, this is not realistic – in reality, the maximum radii of jovians (that aren’t in star-hugging “Torch orbits”, at least) is between 70,000 and 80,000 km, because at that point adding more mass just causes them to self-compress further. In other words, Jupiter is about as big as a Gas Giant can get in terms of radius, though more mass can be piled into it and it wouldn’t get much bigger. So I set the upper limit at 70,000 – 80,000 km here, which results in an upper mass limit of about 8 Jupiter Masses (still too small for a Brown Dwarf though).

Finally, I simply calculated the MMW (and blackbody temperature and mass) of each planet instead of attempting to encode the tables directly. The MMW table in the book isn’t accurate in a general case anyway – this is discussed further in the Observations section.

Aside from these changes, I was able to translate the worldgen rules pretty faithfully into the program. Once that was done, I could set up runs that would generate 100,000 systems to investigate how many of which types of stars and worlds were created.

Continue reading ‘[2300AD] The GDW 2300AD Worldbuilding system: Part 1 – Investigation’