[Space] GURPS Handbook of the Planets

[Agemegos]

Originally Posted by Nemoricus

That should do quite nicely, though it might fail for the less massive gas giants like Neptune and Uranus, where hydrogen isn't quite as dominant as it is in Jupiter and Saturn.

My grasp of physical chemistry is weak, but perhaps it would be possible to use a weighted average of the the specific heats of the chief constituents.

I'm aware. I'm just saying that a big gas giant might have that mass spread across more major moons.

Aah! Good point.

Out of curiosity, what modifications have you made to your private version of the generator?

• I set it up to read stellar data out of a catalogue (based on XHIP, but with random infill of missing data) instead of generating the star at random.
  
• I altered the Gas Giant Arrangement Table to produce far fewer Eccentric and Epistellar results and somewhat fewer "no gas giant" results.
  
• I replaced use of the Orbital Spacing Table with a continuous random variable.
  
• I tweaked the Orbit Contents Table to get more Terrestrial Planet Standard and Terrestrial Planet Large. (I might have over-done that, since I am now getting rather more habitable planets than my revision of Dole led me to expect).
  
• I used the same placement of moons as is in the Handbook, but that's different from Space.
  
• I used a continuous random variable instead of a 3d6 roll for Atmospheric Mass.
  
• I replaced the method for resoving the Ocean/Garden ambiguity, which multiplies the age of the system by the level of visual illumination on the planet, and then compares that to a randomly determined expected time of oxygen catastrophe.
  
• I tweaked the threshold for Marginal Atmosphere to get fewer of those.
  
• I replaced the die roll for hydrographic coverage with a continuous random variable.
  
• I altered the definitions of the climates so that a planet that ought to be frozen to the equator is "frozen", and one that is warmer than 30 C at the poles is "infernal", and so as not to use "tropical" as a temperature category.
  
• I altered the determination of size, mass, and gravity to use a continuous random variable instead of the die roll for density.
  
• I coded a modifier to temperature for worlds with water oceans and active volcanoes or tectonics, to reflect stabilisation of the temperature at about 15 C by the carbonate-silicate cycle.
  
• I calculate the level of illumination with visible light, but that was an Easter egg in the Handbook already.
  
• I calculate the apparent periods and apparent sizes of the sun and the primary and any moons, but that was an Easter egg in the Handbook too.
  
• Instead of using Space's "habitability" score I determine factors for the gravity (based on data in Dole), atmosphere (with adjustsments for volcanism and tectonism), hydrographics (based on the proporition of any land surface like not to be arid), temperature (based on the proportion of the world's surface likely to be between 0C and 30C, the limits of agriculture), level of visible illumination, and day-length (following Dole, but I would like to improve this by calculating diurnal temperature variation and windiness and basing on those instead). Then I multiply those together to determine a habitability index on a scale from 0 to 100%. Earth comes out to 75.6%, chiefly limited by the presence of arid deserts and cold polar regions. Then I calculate a relative carrying capacity that depends on the square of diameter, the proportion of the surface not covered with water, and slightly different factors for the things that determin the habitability index. That's adjusted to make Earth come out to 1.00.
  
• I adjusted the "hydrographics" score of tide-locked worlds so that water on the night face doesn't count unless the night face temperature is above freezing point.

That's about it.