The third, relatively loose, faction of The Expanse universe is called the Outer Planets Alliance. It's members are Belters, who live on asteroids like Ceres and Eros, as well as a number of space stations on both sides of the asteroid field.

However, are there any actual "planets" in the OPA? I know that the outer planets are uninhabitable (sans Pluto) due to being gas giants, but their moons are not.

Are there any moons where people live? Not just work, live, like on Ceres.

Please refrain from book spoilers - if there is are locations like that described in the books that haven't been shown in the TV show, please mention them without any context.

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    If you count Pluto as a planet (your wording suggests so) then Ceres counts. Its as much a planet as is Pluto. So, does Pluto count in your perspective as "planet"? Mar 13, 2017 at 10:44
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    @AngeloFuchs sorry, I've lived longer with Pluto as a planet than not. Old habits die hard. That aside, Ceres is less than 45% of Pluto's size, there's a difference. I want to think that Pluto is a planet! But, I am not the one to make the call, so... nope, Pluto is not a planet <single tear>
    – Petersaber
    Mar 13, 2017 at 13:53

3 Answers 3


Yes. Like you said yourself, the outer planets themselves are not habitable, but several of their moons have humans living on them.

Ganymede, Titan and Europa all have human settlements.

Io and Titania possibly also have humans living on it who don't primarily work there, but perhaps not (depends on what you're actually after with your question; Titania houses a research base housing 5000 people, which probably requires a larger infrastructure with non-scientists working there).

  • I've accepted the answer but I forgot an important thing. Ganymede is under Mars control, not OPA. So while these settlements exist, are any under OPA control, like Ceres?
    – Petersaber
    Apr 7, 2017 at 20:57
  • @Petersaber Sorry, but I can't answer that in detail while still adhering to the wish you stated in your last paragraph. The answer is yes.
    – tobiasvl
    Apr 7, 2017 at 21:24
  • Ok! I won't uncheck the answer in that case
    – Petersaber
    Apr 8, 2017 at 8:29

Well, they inhabit moons ORBITING Jupiter and Saturn, so they are as close to inhabiting those planets as humans are ever going to get. Plus there is Titania around Uranus (not sure if that science station is technically OPA though). They orbit the "outer planets", move with them, etc. So even though much of their structure is in the Asteroid Belt between Mars and Jupiter, conceptually they occupy the "outer planets" in every useful sense from the POV of an Earther or Martian.


I'm going to add an answer which I think is overlooked in the existing (good) answers.

Consider this - one aspect of the OPA which is continually touched on in the novels is that belters feel like they are marginalised by Mars and the UN, that they are treated like second class humans.

Mars and Earth control a lot of life for the belters - a few times the books mention that Mars lowers the price it will pay for ore that is supplied from belter mines, that Earth based companies continually raise prices of medical supplies that belters need, or force up the price of air, meaning belters have to run "lean" and risk their lives.

The whole attitude toward belters is a big sociopolitical issue in the novels.

The name "Outer Planets Alliance" doesn't actually include any planets - it includes a lot of rocks, some stations etc but no actual planets. So why the name?

Its a political manoeuvre - nothing more.

By including "Planets" in the name, its a deliberate political effort to reduce the marginalisation - its a "we are just as good as you are" ploy, one that costs nothing but might at least sway some people. Thats my take on it.

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