I am making a near-future setting that takes place in an alternate solar system that's similar to ours (one planet with life, a moon, and other planets without life and their associated moons).

And it's my understanding, even though I'm not a science expert, that the conditions of our solar system, how the earth is situated in relation to the sun and other cosmic bodies, is a "fixed requirement" for life. Making drastic changes to the makeup of our solar system might create a situation that wouldn't have allowed for the hospitable conditions for life that exist on earth.

Now, as I said, this is just what I've caught and I'm not a science person so please correct me if I'm wrong :).

So my question is, how much of the solar system can I change without making life on earth implausible? For example: Does Jupiter have to be a gas giant due to the events that are also related to the conditions we have on earth? Can the earth have three moons without affecting this prospect?

These are not exactly the things that I had in mind for my setting specifically, but I'm just throwing out the kinds of thoughts I'm having.

So in general, what can change and what can't change in order to maintain an earthlike planet in a solar system?

Thanks beforehand!

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    $\begingroup$ There is a very very long list of specific attributes of our Solar System, both large and small, which can be modified without having any effect on Earth. Mercury and Venus can be deleted altogether. Jupiter is quite important, but the outer planets may very well go, or be modified at will. The two tiny satellites of Mars are utterly irrelevant -- could be three, could be none. The exact number of satellites of Jupiter does not really matter. The rings of Saturn have zero effect on Earth. And so on, and so on. This question asks for an unbounded list of allowable changes. $\endgroup$
    – AlexP
    Commented Aug 2, 2019 at 10:47
  • $\begingroup$ @AlexP Thanks for your insight. I understand the question is very broad. Not exactly sure how to narrow it down, but broad general answers like this is what I'm looking for. $\endgroup$ Commented Aug 2, 2019 at 11:53
  • $\begingroup$ Unfortunately, broad general answers are not what the site is for. $\endgroup$
    – Frostfyre
    Commented Aug 2, 2019 at 12:08
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    $\begingroup$ This question is as broad as the solar system itself. $\endgroup$
    – Trevor
    Commented Aug 2, 2019 at 12:54
  • $\begingroup$ Perhaps you could make this less broad by asking "which astral bodies in our solar system have a significant impact on life on Earth and why". Also, not all life is made equally fit. Are you asking about what Humans need to survive, a significant number of species need to survive, or stuff that would kill everything down to the microbes at the bottom of the ocean floor? $\endgroup$
    – Nosajimiki
    Commented Aug 2, 2019 at 20:37

1 Answer 1


So, let's look at the basic reason life exists on Earth: the Goldilocks Zone. This zone is determined specifically by the distance of a planet to its star, given some characteristics of the star (size, brightness, type, etc.). What this means is basically that unless there's a planet(s) that exists specifically to prevent us from having access to sunlight (or gives us too much light at all times), you can do whatever you want to the solar system as long as you make sure that the Earth and Sun's conditions are as they are. If you're going to make the Sun brighter/releasing more light/energy, the maybe put the Earth further away as well, and vice versa. But unless the change is something more direct, no effects will be that noticeable on Earth.

Now, if we made these changes early on in the formation of the system, that would modify the 'domino effect' that led to Earth being formed at all, let alone having life. I'd rather not answer the question for those conditions though, because I don't know enough about the formation of planets to be able to predict that. I hope this helps!

Edit: Atmosphere and in-planet conditions have not been referred to as the asker only asked about the positioning of other planets. The baseline I'm looking at here is the existence of liquid water.

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    $\begingroup$ A caveat is that a large Jovian planet in an orbit close to the earthlike planet could disrupt its orbit or even prevent it from forming (the way that Jupiter is thought to have prevented a planet forming between Mars and Jupiter). $\endgroup$ Commented Aug 2, 2019 at 10:39
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    $\begingroup$ OP is asking for a hard science answer. That aside, I have the feeling you are answering to "What can I change in the solar system without affecting life on Earth?" with "you can change as much as you like, as long as you don't affect life on Earth". Which sounds like a tautology. $\endgroup$
    – L.Dutch
    Commented Aug 2, 2019 at 11:04
  • $\begingroup$ @KlausÆ.Mogensen So if I place planets with entirely different characteristics, but with the same mass and distance to the earthlike planet. This shouldn't be a problem? $\endgroup$ Commented Aug 2, 2019 at 12:01
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    $\begingroup$ Yep. And you can have outer planets as different as you like, up to having a red dwarf star orbiting at (say) 100 AU. $\endgroup$ Commented Aug 2, 2019 at 13:22

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