While I’m waiting for my consulting editor to have a look at The Curse of Steel, I’ve turned back to a project that I’ve been neglecting for too long: the world-building book Architect of Worlds. Several sections of that book already exist in a rough draft, which can be found at the Architect of Worlds link in the sidebar.

The bulk of the material I’ve already written is a design sequence, permitting the user to set up fictional star systems (or to fill in details for real-world systems). The idea is to let SF writers, game designers, tabletop game referees, and so on design locations for interstellar SF settings, using whatever combination of random chance and deliberate choice they prefer. The emphasis is on “hard SF” realism, as far as the state of exoplanetary astronomy will permit, and no dependencies on any specific tabletop rules system.

So far, the draft system permits one to place stars, planets, and moons, and get gross physical properties (mass, density, surface gravity) and dynamic parameters (orbital radius, eccentricity, and period) for each.

The next slice of the system will involve generating the surface conditions for such bodies, at least for the small “terrestroid” worlds that are likely to provide environments for SF adventure. At this point we’re talking about things like surface temperature (average and variations), atmospheric composition and pressure, the amount and state of water (or other volatiles) on the surface, what kind of native life might be prevalent, and so on.

I’ve been mulling this section over for a few years now, since the science involved is a lot more complicated and more difficult to reduce to a set of game-able abstractions.

When I designed a system like this for GURPS Space Fourth Edition, I made a deliberate design choice to reduce all the possibilities to a specific set of archetypes. That provided some backward compatibility with earlier versions of the GURPS system, and with the older Traveller systems that were an inspiration for both. For this book, though, I want to give the readers as much detail as I can, and let them decide what to use and what to set aside. That complicates the design.

So, a very rough overall outline of what’s going to be involved for a given “world” (that is, a terrestrial planet or moon with some likelihood of a solid surface):

• The rotation rate of the world (including cases where the world is tide-locked or resonant with a primary). As a sidebar, this gives us quantities for the length of the natural day, month, and year.
• The blackbody temperature and incidence of stellar wind for the world, based on the properties and distance of its primary star.
• The strength of the world’s magnetic field, and the consequences for the size and strength of its magnetosphere (if any). If the world is a moon (for example, the satellite of a gas giant planet), then the primary’s magnetic field and magnetosphere may be relevant as well.
• The world’s initial budget of volatiles – how much in the way of possible liquid or gaseous compounds was the world left with after its process of formation.
• Atmospheric composition – what volatile compounds are likely to be gaseous at local temperatures, and can the planet hold onto them?
• Atmospheric mass and pressure.
• Hydrospheric composition – what volatile compounds are likely to be liquid or solid instead?
• Hydrospheric mass and prevalence – how much of the world’s surface will be covered by what kinds of liquid or solid stuff?
• Average surface temperature.
• Estimated variations in surface temperature with the position on the surface, time of day, and so on.
• Presence and complexity of native life – which may require a loop-back to adjust characteristics of the atmosphere, hydrosphere, and surface temperature.

All that’s the minimum for what the next section of the book needs to cover. There are a lot of dependencies back and forth here, which is one reason why I’ve struggled for so long to build this piece. I’m beginning to think I see how to design something workable, though. At least enough to get started. More over the next few weeks.