Let's say we are in the moderately distant future. For example, humans are technologically advanced enough so that interstellar travel is possible and Venus and Mars are terraformed. General artificial intelligences are common and implants and body upgrades too. I need a motivation for the advanced humanity to abandon the solar system (or just mars, explained below). But it must leave it in a mostly habitable state.

Here is the context: I want to make a game about humans that were released from cryoconservation for a few generations ago on a empty terraformed mars left by those most advanced humans. The player/protagonist is released in the present and must explore and learn about the current world, a bit like the fallout franchise. The important part is that the new martians could not have been helped by advanced humans; I want them to have adapted on their own and survived independently. The martians needs to be put in cryo waaaaay before the past so that they dont know how to operate/understand most of the machines and things left by the advanced.

  • Why mars? Because of its weaker gravity, it serve as an in-game justification to be able to jump higher and carry more stuff. Basically it makes this aspect of the game design a bit more realistic. Also, I feel like mars would probably be the first planet to be completely terraformed But I don't really have more reasons than that so it could change.

  • Why a few generation? I want the people to be isolated long enough that they could have their own beliefs and doubts about the reason that they are here. I want to make it a final story plot point to discover why the current martian are here. And after a few generation, people mostly would have found a way to survive and found a solution to pretty much every basic needs.

I have possible ideas but they all have something that doesn't really make sense:
  1. It is an experiment. Ancient humans left on purpose to see how life would work out to survive in a event where really few humans are left. But why would they experiment this? If they are advanced enough that they are a multi-planetary(or even multi-star system) civilization, what is the point of testing the loss of a fraction of the whole civilization. Also, in the case that it is only for simulation purposes, at what point does the experiment could be called a success or a failure?

  2. It could be for climate's sake Wall-e style. Humans left mars because after multiple terraformed centuries, they have replicated some kind of climate/ecological catastrophe. And the humans left on mars is only an accident. The problem with this is that it is not really a reason to not send help. After a few generations of surviving Martians, the more advanced humans, still in the solar system, would probably have figured out that they forgot some people there.

  3. It could be giant solar flare that could be a threat to the advanced human's technology. A flare is better than other threats because it doesn't affect the living things as much as other catastrophes, like asteroid impact for example. But I feel like at this point in the future, humans would have figured out how to deal with this.

  4. Maybe Mars was not left on purpose and an extinction event wiped all humans on it. (pandemic, war, rogue AI, a new invention that messed up, etc.) Mars was not worth the trouble to recover and repopulate according to rest of humanity. This has the same problem as the second idea; it is not really a reason to not send help if they realize that there are survivors.

  5. What if the current martian occupation is just descendants from a group that invaded mars at some point and did not come from cryconservation. The older people would have only told thier side of the story to their children and so on for a few generation. The problem is that if this group is smart enough to take over a planet, they are probably smart enough to prepare how to survive the diffculties of the "post-war" world because they caused it and decided to do it.

Also, I think idea 1, 4 and 5 are easier to justify an in-game reason for enemies.

Thank you for helping and sorry for bad english.

  • 1
    $\begingroup$ Welcome to worldbuilding. We don't make your story for you. And you are asking us to do it $\endgroup$
    – L.Dutch
    Aug 24, 2022 at 15:59
  • $\begingroup$ Questions about the motivations of a character, or organization aren't permitted on this site. That's less about establishing a fact of your world and more about how you write your story. We also aren't here to brainstorm or make decisions for you. You've suggested 5 potential reasons, soliciting our opinions about them isn't a good ask for this site. $\endgroup$
    – sphennings
    Aug 24, 2022 at 16:16
  • $\begingroup$ @sphennings Thanks for your inputs! I only checked other "motivation" questions that were asked here and wrote mine in a similar way but I understand how it's not really the point of this site. I was expecting answers like "idea 3 works a bit better if you change blablabla".. $\endgroup$
    – Lewis
    Aug 24, 2022 at 16:52
  • 1
    $\begingroup$ @Lewis If you read our help center it says "If on the other hand you aren’t sure what a character (be it an individual or organization) should do, that is out of scope for the site," If you see other questions that are in violation of this policy you can flag them for moderator attention. $\endgroup$
    – sphennings
    Aug 24, 2022 at 17:02
  • 1
    $\begingroup$ @Lewis Also, for future reference, the help center also says, "To prevent your question from being flagged and possibly removed, avoid asking subjective questions where every answer is equally valid [and] your answer is provided along with the question, and you expect more answers." Those rules exists to help worldbuilders focus on solving problems (one idea has a weakness? Let's fix that weakness!) rather than simply fishing for more ideas. $\endgroup$
    – JBH
    Aug 24, 2022 at 19:33

2 Answers 2


A technological singularity.

The former population didn't go anywhere - they are just no longer recognisable as human.

As brain implants accelerated and transformed human consciousness the difference between biological and machine intelligence first blurred and then disappeared altogether. Eventually the entire population, solar system wide, abandoned their bioshells and fully entered cyberspace.

They are still there, but freed of the biological necessity of living on a planet, the "human" civilisation is now distributed across millions of space craft throughout the entire solar system where most of the resources they now need are far more accessible.


No advanced humans left anywhere.

Your population is from a colony ship that left long ago when people were first colonizing places. Mars had a colony back then and they were working on Venus. The colony ship your people were on got where it was going and turned around because things were not as expected. Your people are not clear about why it turned around and they wound up back in our system.

Landing on Mars they find ruins. People are not there. I like the idea of an alien plague that came back from one of the colony worlds and that spread over the human worlds. As the game goes on your people might find refuges where the advanced humans went to escape the plague. Maybe the plague still exists. It might be different now.

End twist Pandorum style: the plague ship that came back from one of the colony worlds was your ship. Your people actually brought back the alien plague. Their colony ship returned centuries ago. The plague took off from it when it came down. No-one woke them up because alien plague was raging out from the ship. Your people kept sleeping. They only woke up now because of a computer malfunction.


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