New adventure tonight. I have to design Persatuan and come up with an adventure for a very secret agent at DL 5.0 (1950s development).
Note that Persatuan is on the tidally locked planet of a late K star. The GURPS Space generator produced a lot of garden worlds in such situations and rates them as highly habitable. I tweaked my generator sharply to get fewer and rate them rather worse. There are, however, a few around and Persatuan is one of them.
Those figures seem just a wee bit exciting. Merlis & Schneider [2010] (Atmospheric dynamics of Earth-like tidally locked aquaplanets in “Journal of Advances in Modeling Earth Systems – Discussion”) took into account the transport of latent heat and the rotation of a tidally-locked Earthlike planet in detailed atmospheric simulations, and found a difference in temperature of only about 50K in both their slow-rotating (365-day period) and their fast-rotating (1-day period) models. I’m going to halve the range of temperatures around the mean of 27 C.
I’ve just read The City in the Middle of the Night, which has a human-colonised tidally-locked world. They’re effectively living on a narrow strip of land, with cities built where mountains provide some shade from daylight.
That seems to be a widespread model. But looking at Garrett Serviss’s Other Worlds, written when tidally locked Mercury was generally accepted, I see him estimating that 25% of the surface is in the twilight zone, not what I’d call a “narrow strip.” Though I suppose other tidally locked worlds might have a precise strip around the border of day and night.
Not having done the maths, I suspect you’d get some moderately ferocious winds across the temperate zone (hot air from light to dark flowing over cold air from dark to light). The shallower the temperature transitions, of course, the less this will be a problem.
There is quite a bit of modelling available now. It turns out that Coriolis effects are quite significant when the orbital period is short, but I’m still waiting on a series of comparable studies with rotation rates at close intervals from about 24 days to 360. For one bar of atmosphere you seem to get a 50 K difference between dark side and light side, and that is not as great as the difference between equator and poles on Earth. Temperature over the dark side is surprisingly uniform.’
Here is a paper by some people who have done the maths (with the help of quite a lot of computer):
Abstract: We present simulations of atmospheres of Earth-like aquaplanets that are tidally locked to their star, that is, planets whose orbital period is equal to the rotation period about their spin axis, so that one side always faces the star and the other side is always dark. Such simulations are of interest in the study of tidally locked terrestrial exoplanets and as illustrations of how planetary rotation and the insolation distribution shape climate. As extreme cases illustrating the effects of slow and rapid rotation, we consider planets with rotation periods equal to one current Earth year and one current Earth day. The dynamics responsible for the surface climate (e.g., winds, temperature, precipitation) and the general circulation of the atmosphere are discussed in light of existing theories of atmospheric circulations. For example, as expected from the increasing importance of Coriolis accelerations relative to inertial ac- celerations as the rotation rate increases, the winds are approximately isotropic and divergent at leading order in the slowly rotating atmosphere but are predominantly zonal and rotational in the rapidly rotating atmosphere. Free-atmospheric horizontal temperature variations in the slowly rotating atmosphere are generally weaker than in the rapidly rotating atmosphere. Interestingly, the surface temperature on the night side of the planets does not fall below ∼240 K in either the rapidly or slowly rotating atmosphere; that is, heat transport from the day side to the night side of the planets efficiently reduces temperature contrasts in either case. Rotational waves and eddies shape the distribution of winds, temperature, and precipitation in the rapidly rotating atmosphere; in the slowly rotating atmosphere, these distributions are controlled by simpler divergent circulations. Both the slowly and rapidly rotating atmo- spheres exhibit equatorial superrotation. Systematic variation of the planetary rotation rate shows that the equatorial superrotation varies non-monotonically with rotation rate, whereas the surface temperature contrast between the day side and the night side does not vary strongly with changes in rotation rate.
I’m not really familiar with their terminology and notation, but I think the graphs on p. 8 show that in the slow-rotating case the prevailing winds at the surface (σ=1.0) are fastest on the sunny side, in a ring around the subsolar point 45° of latitude/longitude in radius, directed towards the subsolar point at a speed more than 10 m/s but slower than 15 m/s. There is very little surface wind at the terminator.
Evapo-transpiration is shown on p. 6, but that’s for a planet with a wet surface, and Persatuan has only 21% of its surface covered with water.
Examining the figures that Merlin & Schneider present for evaporation and rainfall on synchronously rotating Earthlike planets, I conclude that GURPS Space not only exaggerates the effects of synchronous rotation on the difference of temperature between the unlit and sunlit sides, and on the extent of oceans, but it assigns high Habitability to, and puts human populations on, the wrong ones. It looks as though the twilit zone is not only dimly illuminated but also semi-arid, and as though the sunlit area halfway between the sub solar point and the terminator will be illuminated, but windy and arid. Only the subsolar region seems likely to be well watered by rain. And on an Earthlike world that seems likely to be marginally too warm for human settlement. The human populations ought to go on those tide-locked planets that are a few Celsius to about thirty Celsius cooler than Earth.
Rapid rotation seems to offer a more complicated geographical pattern of tempterature and rainfall, and therefore some escape. But not very much because the areas affected as not extensive, and because raininess tends to be displaced in a way similar to warmth.
Furthermore, modelling of ocean circulation that was reported in Hu Y and Yang J, 2013 Role of ocean heat transport in climates of tidally locked exoplanets around M dwarf stars seems to suggest that oceans on the dark side of a synchronously-rotating Earthlike planet would remain liquid under 3–5 metres of sea ice. That suggests the probability of rapid glacial return of what little water did snow out on the dark side. There would be ice-caps on continental masses, but a hemispheric ice-sheet that reduced the ocean coverage by 50% is not to be expected.
Little survives of the treatment of tidally locked planets in GURPS Space. The adjustment to atmospheric pressure seems questionable, the adjustment to hydrographics seems quite excessive, the calculated day face and night face temperatures are too extreme (at least for any plausible settlement candidate), and I think that the Habitability ought to be scored on the day face temperature, not the average temperature.
As in, in some circumstances a particular marriage is compulsory, and then you have to make it even if you are already married. But you can’t take a second spouse unless you are forced to.
Example: June is a member of the Zumil masyarakat only by virtue of being married to Emil. If she leaves the masyarakat it will have to liquidate property or incur debt to return her share. Emil has a brother Ezra, who is married to Donna; they have a son Edhi. Ezra dies of pancreatic cancer. Donna is a member of the Zumil by birth, but she’s entitled to demand a levirate marriage anyway. She fancies Emil and doesn’t fancy becoming a widow, so she asserts her right. Emil has to marry her, and can because he must. Emil’s nephew Edhi thus becomes his stepson. A bit later Edhi falls in love with his maternal cross-cousin Dana, which would be a very suitable match. They plan to marry where Edhi turns eighteen. But then Emil is killed in a tractor-rollover accident. Edhi doesn’t have to marry his mother, because that would be incest; Donna becomes a widow, with attendant loss of status and conjugal rights. But Edhi isn’t related to his stepmother/aunt. June doesn’t want to be a penniless widow, and the masyarakat doesn’t want to pay her off. So she exercises her right to a levirate marriage. Emil’s heir-general is Edhi, so Edhi has to marry June. Edhi is only seventeen, too young to marry Dana, but he can marry June because he must. A bit later Edhi turns eighteen, but now he can’t marry Dana because that would be bigamy. Edhi and Dana conduct an illicit affair, which nobody minds so long as they are discreet, except for June, and June is not willing to seek her only remedy, divorce. She makes Edhi’s home life as miserable as she can manage.
Well, not necessarily. A lot of people seem to have enjoyed watching anime in the days when its cultural references were often obscure. And I’ve read that the bulk of the Athenian pottery output actually was exported to Etruria, where they probably had none of the relevant mythical references at hand.
Yeah, but I think they’d get a bigger fan base if they added the commentary track. I suspect the cost of distributing it across the worlds and getting the money back dwarfs the cost of production.
Then you can have offworld fan communities with favourite commentary writers, and hey, the news says this writer was just arrested for [crime], but we’ve heard their comments about [soap], so we know they’re not the kind of person to do that.
And next thing you know you’re hiring player characters.
Of course you’ll also have the hard core fans complaining that it’s all been ruined by being made accessible to a wider audience. It’ll be dubs versus subs all over.
