[Space] Star system with thirty-six inhabitable worlds?

[Michael Thayne]

Originally Posted by AlexanderHowl

The size of the habitable zone increases by the fourth root of L, so every 16x L equals a doubling of the habitable zone. Giant stars could be useful though, sort of like Darkover, as they can last a billion years, which is more than long enough to make worthwhile to terraform moons. A G2 giant would have a L of 40, meaning that the habitable zone would be at around 2.5 AU.

If you believe GURPS Space rules, the absolute size of the habitable zone doesn't matter. What matters is the ratio between the inner and outer edges of the habitable zone. To see why: that star with a luminosity of 40 has a habitable zone roughly from 4.8 AU (blackbody temp 319K) to 8.4 AU (blackbody temp 241 AU). If one planet is at exactly 4.8 AU, the closest the next planet can be according to the Orbit Spacing Table on p. 109 is 6.72 AU, followed by 9.804 AU, which is outside the habitable zone. Of course, GURPS Space apparently doesn't technically allow you to generate TRAPIST-1. But more than the three planets in the habitable zone TRAIPIST-1 has seems really unlikely, based on what we think we know about how star systems work.

[Johnny1A.2]

Originally Posted by Michael Thayne

If you believe GURPS Space rules, the absolute size of the habitable zone doesn't matter. What matters is the ratio between the inner and outer edges of the habitable zone. To see why: that star with a luminosity of 40 has a habitable zone roughly from 4.8 AU (blackbody temp 319K) to 8.4 AU (blackbody temp 241 AU). If one planet is at exactly 4.8 AU, the closest the next planet can be according to the Orbit Spacing Table on p. 109 is 6.72 AU, followed by 9.804 AU, which is outside the habitable zone. Of course, GURPS Space apparently doesn't technically allow you to generate TRAPIST-1. But more than the three planets in the habitable zone TRAIPIST-1 has seems really unlikely, based on what we think we know about how star systems work.

Yeah, but in all honesty, we know very little about how star systems work. Until the last few decades, we couldn't even be certain that there were any star systems other than the Solar System, and our theories on the subject generalized from one example, which is always dangerous. Those theories in retrospect look massively naïve.

So, probably, are our current ones. We have multiple examples now, which is better, but with what are probably heavy 'selection biases', meaning they are not necessarily representative.

We really can't assign much in the way of believable probabilities because our information is so limited.

[Pragmatic]

Luminosity determines Goldilocks zone.

What does stellar mass determine?

I remember using two Sol-size stars in very close orbit to create (to my amateur eyes) a plausible way to have two habitable planets in a system (one close to perfect, one slightly extreme; chilly/tropical or warm/icy).

I think it determines lifespan of a star, the time available for the system to evolve an ecosystem.

[Anders]

Stellar mass determines luminosity and lifespan.

[ericthered]

Trappist-1 was the universe trolling all of the models we had up until then.



The habitable zone equations and the 1.4 ratio should hold. Trappist-1 is a beautiful mosaic of stacked resonances. Outside of that, the ratio holds, and the black body temperatures are not going to change much either.



I build a graphical star system editor using the gurps:space equations, and the luminosity of the star doesn't change the size of the goldilocks zone in terms of orbital ratios. There is a rule in space that sets a minimal orbital distance between planets, but that's one rule from space that the new exoplanet data seems to throw out, and I'm frankly not surprized. So you can fit two planets into the goldilocks zone of gurps space.



Also, garden/ocean planet range in gurps space and astronomy habitable zones are related but different concepts. One thing Trappist-1 did really well was demonstrate how fast and loose the "Goldilocks" Zone astronomers had been using was.

[Anders]

You may be able to throw in three habitable orbits, depending on how thick the atmosphere is (and its composition).

[scc]

I shouldn't have to say it but this sort of system works best as the only system in your setting. As a one-off system to encounter it's interesting but not really that impactful and a the capital of some grand empire/home base system for the players it has this nice semi-mystical vibe to it, but it really shines as the only system in a setting.

Now any race/civilization that evolves in such a system is going to be much more interested in (space) flight then we are, funding will be give much earlier and much more freely, so colonies will be set up with the minimum required tech to establish them. At this point the questions become things like how low can I set the gravity to encourage spaceflight without encountering future problems?