[Phantasm]

Originally Posted by scc

What's a reasonable volume of space to have, say 130, inhabitable planets in then? 100 ly? 50?

In a 20 ly radius around Earth, there are 22 stars in the K, G, and F range, including four binary* and three trinary** systems, which have the potential for stable orbits in the life zone. If we assume even half of those have an inhabitable planet in the life zone, that's 11 potentially inhabitable planets. That number almost doubles if you include M0 to M3 type stars.

So I'd say between 75 and 150 lightyears is a good radius for 130 inhabitable planets, depending on how you have the population density of stars.




* Counting Alpha Centauri as a binary here, with Proxima far enough out to not affect the other two's life zones. Procyon, 61 Cygni, and 82 Eridani are the other binary systems, and 82 Eridani is a close-orbiting binary with a combined brightness in the G5 range. Procyon, like Sirius, has a white dwarf companion, so likely does not have an inhabitable planet.


** 36 Ophiuchi, with two K-type stars 8 AU apart at closest approach, and a third K-type 4340 AU away from the binary; Gliese 570 is a K-type star with a close-orbiting binary reaching M1 brightness; Omicron(2) Eridani, a K-type star with a white dwarf and a red dwarf orbiting each other, getting 20 AU away from the main star at closest approach