Few phrases are as evocative as “tidal locking,” also known as 1:1 spin-orbit resonance. Put simply, this is the condition wherein the time it takes a world to rotate around its axis is the same as the time it takes to orbit its parent body once. Consequently, one side has a perpetual view of the world’s parent body, while the other side is always facing away from the parent body. The closest example to hand is our Moon, whose Earth-side face is very familiar to us and whose far side was unseen by humans until the advent of space probes.
Many authors have been fascinated by the phenomenon of tidal locking, which can set up some great plots. Take these five vintage examples.
“Parasite Planet” by Stanley G. Weinbaum (1935)
Although the region at the very center of tidally locked Venus’ sunward side is parched and lifeless, conditions in the Hotlands, closer to Venus’ twilight zone, are more conducive to life. Indeed, the region is so filled with exuberant species that visitors from comparatively chill, sparse Earth are hard-pressed to avoid being eaten by one or another of Venus’ ravenous lifeforms, whether animal, vegetable, or fungal.
Prudent humans remain far from Venus. Desperate people, like Hamilton “Ham” Hammond, seek fortunes there. As far as Patricia Burlingame is concerned, Ham is nothing but a trespassing poacher. How inconvenient, therefore, that circumstances should force the pair to cooperate for survival. Surely, once their dangerous journey over, the future Mr. and Mrs. Hammond will part ways, never to speak again.
Due to the difficulty of measuring Venus’ rotational period, there were a wide range of estimates available to SF authors concerning the length of the Venusian day. To my knowledge, nobody suggested that Venus’ sidereal rotation would be 243 Earth days, longer than Venus’ 224.7 Earth-day solar year. Venus’ synodic rotation period of 117 Earth days would be a fascinating detail to include in a story set on Venus. If only conditions there were not far more hostile to terrestrial life than Weinbaum could have envisioned.
“Brightside Crossing” by Alan E. Nourse (1956)
Mercury’s Brightside is a sunbaked desolation where lead flows like water. Brightside at Mercury’s perihelion, when Mercury is at its closest to the sun, is even hotter. Naturally the same sort of brave explorers who’ve left corpses scattered on Mount Everest would find Brightside irresistible. The fact that nobody has ever succeeded in crossing Brightside at perihelion only makes the prospect more tantalizing.
Peter Claney’s expedition failed like all the others. Unlike every other explorer who challenged the Brightside, however, Claney survived the attempt. Aware that James Baron is planning his own foray across the Brightside, Claney seeks Baron out. Claney hopes the story of his failed crossing will deter Baron and save lives…as though that would have worked had someone tried something similar on Claney himself.
Mercury was believed to have a 1:1 spin-orbit resonance until 1965, when radar observations revealed that the planet rotates three times for every two revolutions around the Sun. This 3:2 spin-orbit resonance is both very cool and something that instantly rendered obsolete a lot of old-time SF stories, such as this one.
Hothouse by Brian Aldiss (1962)
Over the eons, Earth slowed until one face was locked to the Sun. On that face, life thrives, although not human life. Unable to complete with the monstrously vibrant life that now dominates the Earth, humanity has been reduced to a small handful of perpetually-imperiled tasty survivors. Human extinction must be only a matter of time.
A devastating crisis convinces the elders to divide the tribe: The children will find their own way, unburdened by the old people. The ancients will “go up,” seeking the final fate of those who have lived too long. The humans could be forgiven for believing “go up” is just a fancy way of saying “wander off and get eaten politely out of sight.” The truth is far more bizarre.
Not only is the Earth tidally locked to the Sun but the Moon has retreated to a Lagrange point, where it enjoys a position so fixed with respect to the Earth that a vast network of vines links the worlds. It’s just possible that scientific plausibility was not Aldiss’ primary goal.
Day by Night by Tanith Lee (1980)
Vitro’s world has a single, parched hemisphere facing its sun, and a single frozen hemisphere facing away from its sun. Why anyone would colonize the world is unknown. Nevertheless, someone must have, for Vitro and her people live in fragile artificial habitats on the nightside.
The knowledge needed to repair the habitats is as lost as the planet’s history. When aristocrats’ “Residensias” break down, the inhabitants must appeal to fellow aristocrats for humiliating charity or worse, accept relegation to the slums. Aware that her own Residensia is dying, Vitro chooses a third option: frame rival aristocrat Casrus and appropriate his home. Too bad for Vitro that she formulated her cunning plan while lacking certain vital information about her world.
Lee has judiciously set her story on an unknown exoplanet, far, far away from the spying apparatus of story-spoiling astronomers. Thus, unlike some older stories I could name, science has not rendered this tale obsolete.
Four Hundred Billion Stars by Paul J. McAuley (1988)
Eight light-years away from the war between humans and their alien enemy, a habitable world orbiting an obscure red dwarf presents an enigma. Simple math would deduce that the tidal forces working on the terrestrial world would lock it to its sun just as the Moon is locked to Earth. Observation reveals that this is not the case. A million years ago, someone or something increased the planet’s spin and introduced an ecosystem.
Proximity to the enemy is suggestive. Are the enemy and the beings who brought life to this formerly tidally locked world the same? Telepath Dorothy Yoshida is dispatched to the world to find out. Unravelling the secret history of the Milky Way will be an adventure, one from which many of Dorothy’s companions will not be returning.
Dorothy is on my list of characters with whom never to go camping.
Current models suggest that even a modest atmosphere would be enough to allow heat transport to keep all the volatiles from solidifying on the night side. I do not believe that was clear when this novel was written.
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This is, of course, a very small sample of the stories I could have chosen. It may be that you have your own favourite thrilling tales of tidally locked worlds. If so, regale us with their titles in the comments, which are as ever below.
In the words of fanfiction author Musty181, four-time Hugo finalist, prolific book reviewer, and perennial Darwin Award nominee James Davis Nicoll “looks like a default mii with glasses.” His work has appeared in Interzone, Publishers Weekly and Romantic Times as well as on his own websites, James Nicoll Reviews (where he is assisted by editor Karen Lofstrom and web person Adrienne L. Travis) and the 2021, 2022, and 2023 Aurora Award finalist Young People Read Old SFF (where he is assisted by web person Adrienne L. Travis). His Patreon can be found here.
Charlie Jane Anders The City in the Middle of the Night and Stephen Baxter’s Proxima imagine tidally locked worlds that are very different and show the contemporary variety of the form.
Well, the world of Zelazny’s Jack of Shadows is half SF …
Story : One face (1965), by Larry Niven , in collection “Inconstant moon” (1973) , about a spaceship that after an accident, arrives to the earth in a distant future, that is now tidally locked.
In Poul Anderson’s Swordsmen of Lost Terra, the tidally locked planet is Earth.
Isaac Asimov’s short story, ‘The Dying Night’, included in his collection of Wendell Urth stores entitled Asimov’s Mysteries, relies upon the assumption that Mercury is tidally locked with one face always toward the sun.
There was an interesting post on the 2300 AD facebook group some years ago that suggested that not only was tide locking an issue with red dwarf stars, it was likely to be an issue with K-class stars as well. Of course, now I cannot find it.
In Dave Duncan’s West of January the people who surveyed the planet thought it was tidally locked – but it’s not, quite. This has major repercussions for the colonists.
“Current models suggest that even a modest atmosphere would be enough to allow heat transport to keep all the volatiles from solidifying on the night side. I do not believe that was clear when this novel was written.”
That’s right. That research came along in the late ’90s and early 2000s. Before then, it was generally assumed that a tidally locked world would have only a very narrow habitable band along its terminator.
There are actually two Star Trek novels from that era portraying tidally locked worlds in that way. Jerry Oltion’s 1996 Original Series novel Twilight’s End involves a plan to use hundreds of massive impulse engines to restore the planet’s spin and make it fully habitable; it’s a fun scientific problem-solving novel, more hard-SF than a lot of Trek fiction, and I’m sure if Oltion had written it later, he would’ve taken the new models into account. The 2001 Next Generation novel Section 31: Rogue by Andy Mangels and Michael A. Martin uses a tidally locked planet as its main setting, portraying it as a barely habitable hellhole because of the extremely narrow habitable zone, the lack of surface water, and the endless gale from the scorched dayside to the glaciated nightside. Its authors evidently were not aware of the new models just emerging around that time.
Larry Niven’s first sale, “The Coldest Place,” was written and purchased when scientists still though Mercury was tidally locked. In between purchase and publication it was discovered that Mercury did rotate. The story was still published, with a disclaimer.
Bladrak@9: Dang it, I had thought of that story, but misremembered it as being set on Pluto. Well done.
If I remember rightly, Robet L Forward’s “The Flight of the Dragonfly” exrplores a binary pair of planets tidally locked to each other, so close they are near the Roche limit and share a common atmosphere.
11: Sheffield also wrote about such close orbiting pair, only learning that Forward was working on the same idea thanks to a chance conversation with Forward.
@David Whitmarsh
Also true of The Wooden Astronauts by Bob Shaw.
@10, he had another story from the same collection that was set on Pluto. The narrator ends up taking his helmet off and his brain survives and he remains conscious because of superconductivity, I think. I haven’t read it in yeas.
M.J. Engh’s Wheel of the Winds was, as I recall, set on a tidally-locked world, and featured a circumnavigation of it. The circumnavigators were working with a pre-industrial technology, but they were still able to deal with the intense cold of the the dark side, which suggests that there was some atmospheric mixing.
Since it doesn’t earn me any money these days I might as well mention that I wrote Planets of Peril, an RPG based on Weinbaum’s SF which includes all of his fiction that’s out of copyright in Europe – there’s one story in the vaguely-defined “planetary series” that’s still in copyright here since it was a posthumous collaboration with his sister, but I’ve used his version of Venus as part of the game setting with one adventure set there.
All readable free on line or downloadable here:
https://www.forgottenfutures.com/game/ff11/index.htm
Please ignore anything that asks you to register as a user – it’s all freebies now, though if you feel generous there’s a Paypal tip jar on the front page of the site. And this is a Venusian native from one of the swampier bits…
@14, that’s “Wait It Out”.
@@.-@: I don’t know Swordsmen of Lost Terra, but Anderson contributed a story and an essay to Medea: Harlan’s World, and if memory serves me correctly The Trouble Twisters is also set on a tidally locked plant.
Elsewhere, while not the setting, tidally locked worlds turn up as colour in Asimov’s Foundation series and Niven’s Draco’s Tavern and Known Space series.
The early Traveller adventure Across the Bright Face is set on a world that isn’t tide locked but sort of acts like it: it’s in a 1600 year orbit around an A4 V star, and its axial tilt is very close to 90°. In 1105, its axis points very close to the star, so most of a hemisphere exists in permanent (and rather uncomfortable) day.
19 that was the first Traveller scenario I ever played!
@18/stewart: You’re right about “The Trouble Twisters” (the story, not the fixup-novel collection of the same title which includes it) being set on a tidally locked world. Anderson doesn’t portray the climate difference between the hemispheres as extremely as other examples I’ve read, just saying the dayside is mostly desert and the nightside mostly frozen. So he may have made a lucky guess.
My goodness. The range, the same enthusiasm, the scale of stories you must have consumed. Sigh, definitely would have loved to have been there.
The planet Anarchaos, in the novel of the same name by Curt Clark (a pseudonym of Donald E. Westlake) is tide-locked to a red giant, but it’s far enough away that the sun-facing side is habitable. The planet also has no government or laws whatsoever, hence the name – a combination of “anarchy” and “chaos”.
This is a dark, grim book, not at all like Westlake’s delightful humorous crime novels. I believe it’s also included in “Tomorrow’s Crimes”, a collection of some of his SFF works.
Vitra.
@8) Yes, “The Coldest Place” (from If, December 1964) is a canonical example of a story becoming obsolete between writing and publication due to the advance of scientific knowledge, but I find it amusing that the same editor (Fred Pohl) published a story a whole year after “The Coldest Place” that was also set on a tide-locked Mercury: “The Mercurymen”, by C. C. MacApp, in the December 1965 Galaxy. I don’t recall a disclaimer on that story.
See also “The Sirens of Titan” by Kurt Vonnegut, set in part in caves below the surface of Mercury. In the novel, the tidelocked condition of Mercury makes the planet “sing” with a constant resonant vibration, upon which Mercury’s sole life-forms, “harmoniums,” feed.
25) As I understand it, the news about Mercury broke after Pohl bought the story but before it hit print, and Niven wrote Pohl to ask if he wanted the money back. Pohl wrote back saying basically “are you nuts?”.
Asimov’s short story “Runaround” is set on a tidally locked Mercury. Apparently it was written all the way back in 1941 and later included in “I, Robot” and other collections.
Nightside City by Lawrence Watt-Evans is set in a city on the dark side of a planet when it was thought to be tidally locked. Instead, it rotates, but very slowly. But the city is about to move into the sunlight…
Republished as _Rocheworld_, if folks go looking for it. Like Forward’s other novels (e.g. _Dragon’s Egg_), it had some very cool SF ideas (loved the Christmas Tree and the Flouwen) and some thin characters.
@30/Mike G.: “Republished as _Rocheworld_, if folks go looking for it.”
Always wanted to read that one, never managed to find it. Rocheworld was actually an extended version of Flight of the Dragonfly, or rather, Flight was apparently an abridged version with the full original novel not being released until later.
“Like Forward’s other novels (e.g. _Dragon’s Egg_), it had some very cool SF ideas (loved the Christmas Tree and the Flouwen) and some thin characters.”
That’s putting it generously. As a writer, Forward was an excellent physicist. His son Bob Forward, who wrote extensively for animated TV starting with He-Man in the mid-’80s, was a much better writer. I often wished they’d collaborate, the father providing the science and the son the storytelling and characters. But apparently that wasn’t in the cards.
Though it turns out that Rocheworld had four sequels that Forward co-wrote with his wife and daughter.
Widely reviewed as not very good is a 1960s novel of the far future where Earth has one face to the Sun (aliens did it, they also made us infertile), survivors struggle in twilight and daylight zones, and a brilliant and amoral scientist takes action: from memory, I think he turns the Earth around one quarter turn. Okay…
Michael Moorcock, Shores of Death aka The Twilight Man. I thought I had lots of his books, it appears to be none?