In the first part of this series, I looked at the distribution of systems that the default 2300AD system generated, and examined some of the issues and assumptions that it made. In this article, I’ll present the results of a modified system that addresses these issues and corrects the flawed assumptions, and explain why I made the changes.
Orbital Zones: The Outer Zone now begins at 2.5356*SQRT(L) AU from the star. This is roughly where the “frost line” is (where the blackbody temperature is 175K), beyond which volatiles can condense and gas giants are more likely to form. The new zone between the outer edge of the habitable zone and the inner edge of the outer zone is called the Middle Zone, and cold rocky planets are likely to form there (Mars is located in the Middle Zone in our Solar System, and Jupiter and the more distant gas giants are in the Outer Zone).
The boundaries of the Habitable Zone also need to be adjusted. The K multipliers used in the Life Zone equation in 2300AD don’t match the values shown in the table there – the values in the equation are K=0.72 and 1.45, but the table shows values for K=0.82 and 1.2. Unfortunately, those are both pretty unrealistic! Recent papers have put the inner boundary much closer to 1 AU than 2300AD assumed (between 0.9 and 0.99 AU) and while the outer boundary is less well defined but seems to be around 1.4 to 1.6 AU (see the Circumstellar Habitable Zone wikipedia article).
I will assume here that the habitable zone goes from K = 0.9 to K = 1.4 – this lets us have a full range of environments in the habitable zone without things getting too extreme. So K = 0.9 for the inner edge of the Habitable zone, K=1.4 for the outer edge of the Habitable zone, and K=2.5356 for the border between the Middle and Outer Zones.
Continue reading ‘[2300AD] The GDW 2300AD Worldbuilding system: Part 2 – Realistic Version’