I've reviewed Jon Zeigler's preliminary draft and sent him a first tranche of comments. As soon as I get a replacement for my two defunct scientific calculators I'll run the sequence a couple of times and provide more comments.
Compared with his previous effort (the Basic and Advanced star system generation sequences in GURPS Space 4th
) the planetary science has been substantially brought up to date, reflecting fifteen years of rapid scientific discovery. There has been a significant extension of scope in that the generator now produces a detailed composition of the atmosphere. I am impressed that it takes care to make the greenhouse effect on the planet's surface temperature consistent with the greenhouse forcing values of the minor constituents of the atmosphere.
On the other hand the "Basic" approach (design or generate a planet to taste, calculate its orbital position, and then generate the rest of the system around it) has gone. The new system has achieved a large part of its streamlining by leaving out the tidal calculations and reducing the calculation of tidal braking to a sketch. It also omits the effects of tidal locking on the temperature and volatiles of the day and night sides, though perhaps that will return in a later draft.
Most of the additional work and detail has gone into the developmental process of the star system: mass of the protoplanetary disk, degree of orbital migration of the key gas giant, whether there has been a Grand Tack, whether one of the primordial gas giants was expelled from the system by orbital shenanigans…. It does inform the outcome, but I wonder whether it would not be better to roll on a table of outcomes in terms of overall system architecture and save the user's patience for detailed surface conditions on habitable planets. Apart from the composition of the atmosphere (which has been done), the extensions that I wanted to see were
- provision for generating systems around real nearby stars, using data from astronomical catalogues that usually lack figures for mass, age, and metallicity,
- the illumination level,
- the boiling point of water at the surface,
- the salinity of the oceans,
- the scale height (or half height) of the atmosphere,
- the altitude limits of respiration,
- the effect on aircraft operational ceilings,
- the practical minimum altitude of a circular orbit, with the corresponding orbital period,
- the surface relief — how high are the mountains and plateaux?,
- the number of convectional cells in the global atmospheric circulation, the zonal wind strength, and the vorticity — word scales ("low", "exreme" etc.) would do,
- the temperature of the thermal equator (or subsolar point) and polar regions (or terminator and night side),
- the equator-ward and pole-ward (or subsolar-point-ward and terminator-ward) limits of agriculture.
As a GM or writer of planetary adventure I'm more interested in "Where on this planet do people live; can they make good coffee?" and less in orbital migration five billion years ago, than I am as an amateur of modern astronomy.
Is that too much figuring-out to expect for someone working with a pencil, paper, a handful of dice, and a scientific calculator? Yes, perhaps it is. But that gets us back to what I said in my first comment in this thread. Jon Zeigler's Architect of Worlds
is going to be distributed as a PDF. Everyone who reads it is going to have a computer right there. They would get much more use out of a program or interactive website than they would out of an algorithm for manual execution.
I hope that I have already bought my last petrol-burning car. I'm pretty sure that I have bought my last star-system generator for use with dice and calculator.