What, no love for CoriW's post?
I'm surprised there's not been more interest in this subject. Presumably we'll be spending plenty of time in space in Limit Theory obliterating with hot electric death anything that moves... but what about those among us (I know you're out there!) who are looking forward to trading and exploration and the more civilized ways of interacting with strangers?
That stuff seems more likely to happen on or near planetary-type bodies, I would think. (And Josh
has been talking about planet generation lately.) So I'd like to hear more of people's thoughts about what sort of variation they'd like to see for orbital objects.
As a starting point -- I don't necessarily endorse it as a final answer for a game, but you have to start somewhere -- the Planetary Habitability Laboratory (PHL) maintains a
Habitable Exoplanets Catalog. It suggests a
Periodic Table of Exoplanets, arranged as a matrix of 18 possible planetary categorizations. It's based on six size/mass categories, from tiny (Mercury-size) rocky worlds to Earth-size planets to "small" and large gas giants, and three distance-from-star categories: Hot, Warm (habitable zone), and Cold.
Here's their
categorization of bodies in our Solar System:

- PT_Solar_System-sm.jpg (93.19 KiB) Viewed 1412 times
(Note that the categorization in this diagram of Venus as a "Warm Terran" world may need to be adjusted to a Hot Terran based on a suggested revision of the
habitable zone calculation by Penn State researchers. This new model puts Earth at the inner, hotter, edge of the zone, and Venus well inside it.)
There are two other main ways of coming up with a system for planet type generation:
1. A simple list of planet types. This could be something like "Mercury, Venus, Earth, Mars, cold Venus, hot Mars, gas giant" or have either more or fewer world types. Even simpler might be "rocky hot, rocky temperate, rocky cold, gas giant" with procedurally generated terrain types to match. This approach gets planets dealt with as quickly as possible, allowing more time for other parts of Limit Theory to be developed.
2. A grid similar to the PHL's but using different criteria, such as amount of solar flux received, "daily" temperature range, atmospheric pressure, atmospheric composition, amount of water present, primary mantle composition, and so on. It might be fun to be able to specify water worlds, snowballs, jungle planets, ammoniac oceans, "heavy" worlds, young worlds still burning as they're bombarded with protoplanetary disk debris, high-pressure worlds where humans would have to find mountains to live on, silicon-rich worlds littered with quartz and gems, and a whole host of even more exotic places. These could emerge naturally from a grid showing the intersections among many basic planetary characteristics, and this could be used to determine not only the general look of a world, but some of its gameplay-specific features as well, such as natural resources and the forms of alien life present. This approach allows for more kinds of gameplay related to planetary type, as well as making the whole game much more visually interesting.
I like the "planet types emerge from their multiple characteristics" model for planet generation, myself, but I can see the pros and cons of both systems.
What do you folks think?