By habitable worlds I mean worlds where humans from Earth could live without spacesuits or airtight enclosed habitats.

The creator of this website attepted to build the ultimate solar sytem, a scientifically plausible one with the greatest possible number of habitable planets.

In old science fiction stories from the pulp era it was common to depict our solar system with at least three habitable worlds, Venus, Earth, and Mars, and there were sometimes stories and series with many more habitable worlds.

So which story, series, movie, tv show etc. depicted the solar system with the most habitable worlds, to compare with the supposedly scientifically plausible "Ultimate Solar System"?

Edit 9:58 PM July 4, 2015 I should have added NATURALLY habitable worlds.

For example, in Jack Williamson's Legion of Space stories the solar system has been terraformed to have countless habitable worlds. Even many small moons and asteroids have had breathable atmospheres created, and those atmospheres are kept from floating away into space by artificial gravity fields which also give a feeling of normal gravity.

So in that story hundreds of thousands of objects in our solar system could have been terraformed and colonized.

Edit 10:14 PM July 5, 2015 And in the future it may be possibly to build countless millions of ARTIFICIAL habitats in space out of asteroids, comets, Trans Neptunian Objects, and smaller moons. For example, for each trillion (1,000,000,000,000) Humans living in habitats with average populations of 10,000 to 100,000, there would be 10,000,000 to 100,000,000 space habitats.

So the number of NATURALLY habitable worlds in our solar system in any science fiction story is likely to be very much smaller.

  • So we don't all have to visit that website, how many habitable worlds does the "Ultimate Solar System" have? Is 36 the number to beat? You're asking for a story with three dozen habitable worlds in the solar system? I guess terraformed worlds don't count, they have to provide shirtsleeve environments in their original unmodified state, have I got that right? – user14111 Jul 4 '15 at 21:44
  • @MajorStackings I think you missed "in our Solar System"? – user14111 Jul 4 '15 at 21:46
  • You don't have to equal or beat that "Ultimate Solar System", you just have to find the story with the greatest number of naturally habitable planets, moons and other bodies in our solar system, no matter how unbelievable their habitability may be. I think that would make an interesting comparison. – M. A. Golding Jul 5 '15 at 1:51
  • My own answer has the current record number of fictional naturally habitable worlds in our solar system that has to be beaten by a candidate series. – M. A. Golding Jul 6 '15 at 2:43

One candidate would be the movie 2010: The Year We Make Contact (and the book on which it was based, 2010: Odyssey Two). At the climax of the story, Jupiter becomes a second star in our solar system, and its moons become planets. The unidentified alien race which caused this chain of events then sends a message to humanity:


The story ends with an image of Europa, now teeming with life. Although we don't know for sure that the other new planets (formerly moons) are habitable, the message clearly implies that this is indeed the case - we are told to "use them together... in peace", and it is hard to imagine how we could use planets that are not capable of nurturing life.

Jupiter has at least 67 moons at the most recent count, which could mean that there are now as many as 68 habitable planets in the solar system (Jupiter's 67 moons plus the earth).

However, we don't know how many of Jupiter's new planets are actually habitable. It is probably safe to assume that some of them are not viable. I don't know if the book addresses this issue, but the movie certainly doesn't. If we assume that half of the new planets are habitable, then the number of viable worlds would be about 34, including the earth. If a third of the new planets are habitable, the number of viable worlds is closer to 23, including the earth.

In any case, the number of viable worlds in 2010: The Year We Make Contact/2010: Odyssey Two is probably quite large.

  • 1
    Excellent! I think Mars Trilogy and 2010 are probably about on par... but actually unknowable since neither author explicitly counted (e.g. which moons, and which asteroids). – Lexible Jul 4 '15 at 22:03
  • I think you should consider their real sizes, not speculate. – Mithoron Jul 4 '15 at 23:50
  • @Mithoron - The question doesn't mention size, and the book and movie are very vague about what happened to the new planets, aside from Europa. Speculation is all we have to work with. – Wad Cheber Jul 4 '15 at 23:53
  • But asks about atmosphere - that eliminates asteroid moons – Mithoron Jul 5 '15 at 0:00
  • @Mithoron - If aliens can use monoliths to turn Jupiter into a star, they can probably create atmospheres wherever they please. – Wad Cheber Jul 5 '15 at 0:03

Stanley G. Weinbaum's planetary Series had Humans living in more or less (often much less) comfort breathing the local air on Venus, Earth, Mars, Io, Europa, Ganymede, Titan, and Uranus, eight worlds in all.

The Gerry Carlyle stories by Arthur K. Barnes had native lifeforms mentioned on twelve solar system objects (Mercury, Venus, Earth, Mars, Jupiter, Amalthea, Ganymede, Saturn, Titan, Triton, Pluto, and the fictional Almussen's Comet, and possibly on many other worlds which weren't mentioned. And as I remember humans could live unprotected on several of those worlds, though I don't remember if it was all of them.

  • I've taken the liberty of editing all the chatter out of this answer. – Valorum Aug 10 '15 at 22:01

The anime series Cowboy Bebop has to be a strong contender: most of its varied settings are portrayed as terraformed bodies. Piers Anthony's Bio of a Space Tyrant gets an honorable mention for putting people on just about every solar body with a gravity well; however, it runs afoul of your no "airtight enclosed habitats" requirement.

  • See my revised question asking for NATURALLY habitable planets, and my own answer giving the number to beat. – M. A. Golding Jul 5 '15 at 2:46

According to the 1954 book "Kings of Space" by Capt. W.E.Johns, all the planets in our solar system are habitable.

He describes journeys to a few of them in a ship called Spacemaster, powered by cosmic rays. The only use of Cosmosuits is on a test trip to the moon.

Although better known for his Biggles books, Capt. W.E.Johns wrote a few science fiction books in a similar style. Kings of Space is the first.

  • There were nine books in the series. By the third book, NOW TO THE STARS, Professor Brane and his pals were visiting habitable planetoids. There are thousands of them in our solar system. The Spacemaster wasn't used in later books. Usually they were given a ride in an alien spaceship the Tavona, crewed by humanoid aliens, the Minoans, who were descendants of Martians. They were enjoyable space adventure books. – a4android Sep 22 '16 at 8:31

Kim Stanley Robinson's Mars Trilogy (plus the bonus anthology The Martians) which featured over the next few centuries colonization and varying degrees of terraforming:

  • Mercury (Whoa! Not quite terraforming, but the establishment of a roaming domed city that is constantly keeping on the dark side of the planet)
  • Venus
  • The Earth, remaining habitable (although altered by a few centuries of sea-level rise)
  • Mars (Duh! :), and it's moon Phobos (for a time).
  • Many asteroids (hollowed out, rotated for pseudo gravity, and internal artificial "suns" created)
  • Jovian moons
  • Saturnian moons
  • Neptune's moon Triton
  • Pluto
  • Do they colonize the Rings of Saturn too? That must get you up into the millions of worlds. – user14111 Jul 4 '15 at 21:50
  • @user14111 Read it, it's worth it. :) – Lexible Jul 4 '15 at 21:51
  • See my revised question asking for NATURALLY habitable planets, and my own answer which gives the number of habitable worlds to exceed.revised – M. A. Golding Jul 5 '15 at 2:47

You might feel that this doesn't count, but I'm going to mention The Long Earth series by Terry Pratchett and Stephen Baxter.

The basis for the series is that mankind discovers a simple device, buildable by anyone and powered by a potato, that permits someone to "step" into a parallel world. The parallel world is a copy of Earth with minor geographic differences, but with all natural resources intact and unspoiled, because mankind never evolved there. From that world one can step back to the original Earth, or step again into another parallel world, and another, and so on.

During the course of the first book, the protagonists travel over two billion steps in one "direction", until they step into vacuum because the planet is missing in that particular universe. In the second book, another expedition travels billions of steps in the other direction before finding another "gap" where the Earth is missing.

Between the first and second books in the series--I haven't read the rest yet--there are around five billion copies of the Earth, all readily accessible without special equipment.

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