For a decade and a half or so I have felt very uneasy about the things astronomers were discovering about Tau Ceti What with the huge ring of dust and crud surrounding the star and the crowd of chubby planets orbiting it in tight orbits there seemed to be no prospect for the inhabited world there that is such a landmark of Flat Black.
Then I read the following intriguing titbit in the abstract of a paper published last October: We also predict at least one more planet candidate with an orbital period between ∼ 270 − 470 days, in the habitable zone for τ Ceti. So I read the paper (An Integrated Analysis with Predictions on the Architecture of the τ Ceti Planetary System, Including a Habitable Zone Planet, by Jeremy Dietrich and Dániel Apai of the University of Arizona), and liked this bit:
If PxP–4 is close to the widest predicted orbits (i.e., has a period close to ∼470 days), we find that an additional planet may reside in the habitable zone. This second habitable zone planet would then have a period of ∼270 days.
It turns out that Dietrich and Apai used two different models and compared the results. Both predicted planets that seem likely to correspond to the unconfirmed candidates Tau Ceti b, Tau Ceti c, and Tau Ceti d, and both predicted a yet-undiscovered sub-Neptune or super-Earth in Tau Ceti’s habitable zone. But one model (the “period ratio” model) puts it in a 277–395-day orbit, and the other (the “clustered periods” model) puts it in a 406-468-day orbit.
The clustered periods prescription predictions after adding in all 4 predicted exoplanets. The gap between [Tau Ceti] e and the additional inserted planet PxP–4 is large enough for another planet to fit in between, with a period of ∼270 days, at the inner edge of the habitable zone.
It’s not a matter of betting on the extreme edge of a 95% confidence interval. It’s a matter of choosing one out of two plausible models. I can have my habitable planet in Tau Ceti without having to at least tacitly declare Flat Black to be a retrofuture for which I must ignore the last 15 years of progress in astronomy.
Now, Tau Ceti has a mass of 0.783 solar masses, so a planet in a 270-day orbit around Tau Ceti will have a semi-major-axis of 0.7535 AU. And Tau Ceti has a bolometric luminosity of 0.52 L☉(bolometric), so the settlement candidate will receive at least 0.916 times the insolation that Earth does. Its black-body temperature will be only 6.25 K cooler than Earth’s. The only significant changes that I would have to make to my draft write-up on Tau Ceti would be to change its year-length, reduces its solar illuminance to 79% of Earth’s, and to change its designation from τ Ceti III to τ Ceti VII.