Sci Fi with solar-system counterfactuals

Which is to say, a planet or other body is significantly different than in our timeline-the Moon is larger with a biosphere, a moon of Jupiter has intelligent life forms (which we humans nonetheless find incomprehensible or such), or the ruins of a long-dead ancient civilization is discovered on Mars. Any recs along these lines appreciated.

I’m not sure I’m understanding your question, because the Golden Age of sci fi was chock full of stories and novels that assumed life, ancient and/or current, on Venus and Mars. Many of Heinlein’s excellent juvenile novels, for example.

But the first book I thought of was Protector, by Larry Niven.

Journey to the Far Side of the Sun posits a solar system where there is a planet identical to Earth on the exact opposite side of the sun.

From the Earth to the Moon, by Verne, assumes a breathable atmosphere on the Moon.

Stranger in a Strange Land and Red Planet, by Heinlein, have intelligent life on Mars, as does The War of the Worlds.

Harry Turtledove’s A World of Difference the 4th planet from the Sun is about the size of Venus, has an active biosphere, and was named after the goddess Minerva because it’s blue-grey instead of red. Human history is basically the same with a few minor difference until the Viking probe lands and transmits an image of a native Minervan wielding a spear. By 1989 the US & USSR have launched duelling expeditions and end up getting involved in a war between different Minervan kingdoms.

A great example of this is Niven’s story “The Coldest Place”, which depends crucially on the notion that Mercury is tidally locked and always shows the same face to the Sun. Well, it turns out it’s more complicated than that: It is a lock, of a sort, but it’s a resonant lock, such that the planet’s rotation rate is 1.5 times its orbital rate. And as it happens, the discovery of this fact came after Niven’s story was sold, but before it actually saw print. He frantically wrote up the editor, saying that the story had to be pulled, since it was now out of date. The editor wrote back, who cares, it’s still a great story.

Heck, as late as the 1950s one could read stories assuming Venus was covered in misty jungles and Mars was striped with natural canals.

The Tom Corbett, Space Cadet books assumed both.

Heinlein’s “The Green Hills of Earth” postulates a hot and humid Venus, which was common in 30s SF. What’s notable is that Heinlein knew that Venus was not that way at all before he wrote the story, but wrote it that way anyway.

Clifford Simak’s “Desertion” is set on the surface of Jupiter, which has none. That doesn’t stop it from still being one of the best stories of the Golden Age.

S.M. Stirling’s The Sky People and In the Courts of the Crimson Kings take place in a Solar System where Venus and Mars are both habitable and inhabited, and where the Soviet Union survives into the 21st Century.

C.S. Lewis’ “Perelandra” and the others in that trilogy I suppose imagined a Venus that is like one giant ocean with floating islands that are hard to walk on and such. It was supposed to be like Eden. Lovely place really.

In Jay Lake’s Clockwork trilogy, the solar system is a vast clockwork construct. A life-sized orrery basically, where people can look up from Earth and see all the gears and wheels and so on that guide the planets in their courses, including Earth.

Unless a storyline overtly involves time travel, a Flash Gordon comic strip published in year X is always set in year X. So the stories always take place “here and now”.

But, in Flash Gordon’s universe, mad scientists don’t keep their inventions secret. As a result, earthlings have been colonizing other planets since the 1950s, and other stars since the 1960s. So Flash’s solar system is a much busier and more crowded place than the one we know.

There are a LOT of “Counter-Earth” novels and movies. John Norman’s Gor series is set on such a counter-earth.
You’re wrong about Verne assuming a breathable lunar atmosphere – he never has anyone land on the moon. You must be thinking of H.G. wells’ First Men in the Moon, which DOES assume a lunar atmosphere. So, surprisingly, does fritz Lang’s Die Frau im Mond, and a lot of surprisingly late bad SF films.

Verne did, however, imagine a breathable atmosphere and earth-type gravity on a comet in Hector Servadac (AKA “Off on a Comet”). A lot of episodes of the original Twilight Zone seemed to assume the existence of asteroids within our solar system that had comfortable temperatures, earth-normal gravity, and a breathable atmosphere. Even as a kid, this bothered me.

Sorry-knew that the Golden Age of SF had many stories like that-looking for stuff which is more recent I guess. Responses can still go either way tho.

I was going to post these. Basically Venus and Mars were the Planets of 1800s fiction. Mars is a desert world with ancient civilizations and Venus is a steamy prehistoric jungle world.

Apparently the idea is “what if the Solar System had actually formed differently than it did” rather than “what if conditions on the planets were what they were once thought/hoped to be”.

I can’t believe I’m the first to mention Barsoom…

I can’t remember which one, (maybe John Carter of Mars), but he went to Jupiter and it was very different, too.

In the Larklight novels by Philip Reeve, all the planets, moons, and asteroids have breathable atmospheres and most of them have life.

Asimov’s Lucky Starr novels were accurate when they were written, but were revealed to be counterfactual.

In his book, Celestial Matters, Richard Garfinkle describes a universe in which (among many other differences) the Earth is the center of (at least) the solar system.

Worse than that, for those who haven’t seen it. Only the far side has a breathable atmosphere. How that is supposed to work I have no idea. But they clearly didn’t listen to Oberth a lot.

In the '50s people didn’t really get the concept of asteroid, did they? Rocky Jones Space Ranger had this also, plus all sorts of warm habitable planets in the far reaches of the solar system.

As for Verne, I always assumed that the comet somehow scooped up our atmosphere. I guess it is the mini-black hole in the center responsible for the gravity which made it possible. But that anyone could survive the transfer is a lot bigger problem.

In John Varley’s Titan series, several of the moons (e.g., Titan) of the gas giants turn out to be living space habitats.

We don’t know for sure yet, do we?

**The Martian Chronicles ** is a good example of the Planet Stories era version of Mars, with the benefit that you can read it without gagging (except the non-science.) It had Martians, it had a breathable atmosphere, it had canals.