When rolling up worlds for my sector, I used the “hard science” options in the Mongoose Traveller world generation chapter. I do not obsess about perfect realism – this is entertainment and not a simulation – but I prefer my settings to be plausible and consistent enough to allow suspension of disbelief.
However, there is one issue that I ran into almost at once. The rules specify some hard limiting factors on atmosphere. To quote the SRD:
If Size is 0–2, Atmosphere is set to 0. The world is too small to retain an atmosphere.
If Size is 3–4 and Atmosphere is 0–2, set Atmosphere to 0.
If Size is 3–4 and Atmosphere is 3–5, set Atmosphere to 1.
If Size is 3–4 and Atmopshere is 6+, set Atmosphere to A.
The problem is that 41.67% of all generated worlds will be size 4 or smaller, and the vast majority of these will be vacuum worlds or have trace atmospheres:
At the same time, these worlds only suffer from a -2 DM on population at most, meaning that 83.33% of them end up being inhabited with up to “hundreds of thousands” of people.
In my test sector, I ended up with 16 worlds of size 4 or lower with atmosphere A, and 167 with atmosphere 0 or 1 – out of a total of 424. That’s 39%. None of these 167 worlds ended up with a hydrographics score other than 0.
This might be realistic. We simply don’t know at this point, though it does seem that larger world are abundant in the universe. However I do think it’s an issue when 40% of the “Best” worlds of all systems basically look the same. They may be physically different, but they will all be “humans living underground or in domes”. Not inspiring.
Assuming I don’t want to maintain the status quo and do not want to regress to the regular, non-“hard science”, system, I have some ideas that might produce better results.
- Allow denser atmospheres types, perhaps category 2 and 3 (very thin), for worlds of size 3-4. Unfortunately there are no examples for this that we know of. Titan is small (size 3) and has a thicker atmosphere than Earth does. Most In addition, Mars (size 4) is thought to once have had a thicker atmosphere. Both should really be type A though.
- Allow E and F atmospheric types. Both read like reasonable examples; for example if Europa (size 2) was closer to the sun it could potentially be classified as a class F atmosphere.
- Lower the chance for human population. People don’t move anywhere without a good reason; and there’s perhaps none to move to a worthless rock. The benefit of these “crappy systems nobody wants and nobody goes to” is that you can hide things there that in any inhabited system would quickly be discovered and salvaged.
- Change the way size is generated: While there is no reason not to extend the size scale upward a bit (super-earths are quite common) there is no way to do so with 2d6. It might be possible to change to 3d6-3 and either accept the change in distribution or use a lookup-table.
I think I prefer a combination of changing the size roll and lowering chances of human habitation on unsuitable worlds. I’ll take a look at all options in later posts; meanwhile, is there another approach that I missed?