So I found this site through this other question asking generally about what Earth would be like with two moons. However, these responses, like pretty much everything else I've been able to find insofar on the internet, deal with if the second moon was the same or bigger size, existed in a separate plane from our Moon, was in a differently shaped orbit, heavily affected the tides, etc. What I'm looking for is: how small would a second moon have to be in order to only minimally affect the gravitational pulls on both the Moon and Earth, and then also the tides?

I really want to be able to put something like Saturn's occasional moon transiting/crossing into my fantasy story. An example of that are these pictures I found of Saturn's much smaller moon, Enceladus, passing in front of a larger moon, Rhea.

enter image description here

So, like Enceladus here, because of the Moon's already larger than usual size in comparison to Earth, how small would a second moon have to be in order to exist with a similar smaller scale orbit between the Moon and Earth, without affecting anything too drastically? Alternatively, is it possible to have a smaller moon that can be seen without changing things too much, or not?

If it wouldn't be able to be seen, then theoretically how much smaller would the original Moon need to be in order to make this work? I'm incorporating this in a fantasy world with completely original continents/land-forms so as long as I could realistically keep the Earth's environment types intact on it, I'm not so attached to keeping the Moon as large it is. I just really want two moons, lol.

EDIT: I thought it was clear, but what all of my questions are for is I'm asking if there is a way/multiple ways that an Earth-like planet could have two moons in orbit without it becoming unstable. And I'm asking for details - what would the general sizes look like, what the differences would have to result in (such as the tides), etc. Yes I want two moons, but if it wouldn't be realistic, I won't throw them in.

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    $\begingroup$ Your Title, by itself, would be Too Broad. But the body doesn't narrow this; instead it just rambles on about having moons. Your actual thesis seems to be stated by the concluding sentence, «. I just really want two moons, lol.» that's not even a question, and that seems to reflect the post as a whole. $\endgroup$
    – JDługosz
    Commented Apr 19, 2017 at 23:23
  • $\begingroup$ Well I didn't intend to have a thesis in this, I'm asking a question. I literally asked my main question in the first paragraph. The question is: how could I have an Earth-like planet while also having two moons? I'm asking for details on how this could work. You act like I don't have any questions in this post, when my entire post is questions. I thought that by adding that little "lol" at the end would be a nice light-hearted way to end a very question heavy post, but I'm almost regretting it now. If it is possible to have two moons, I want to know how, and if it isn't, then I won't do it. $\endgroup$
    – lilywin
    Commented Apr 19, 2017 at 23:47
  • $\begingroup$ I disagree. His question clearly is quote " What I'm looking for is: how small would a second moon have to be in order to only minimally affect the gravitational pulls on both the Moon and Earth, and then also the tides?" $\endgroup$ Commented Apr 19, 2017 at 23:48
  • $\begingroup$ People just brush through the content... $\endgroup$ Commented Apr 19, 2017 at 23:49
  • $\begingroup$ It was clear even before the edit. $\endgroup$ Commented Apr 19, 2017 at 23:50

1 Answer 1


Our moon has moved farther away, over the span of 4 billion years, due to tides. So any smaller moon closer than the Moon would have since been run down and is no longer present.

A second moon farther away would have to be substantially farther so the movment of the moon doesn’t disupt it.

So look at Earth’s Hill Sphere and see how large it is. That is 1.5 million km. A body twice as far as the moon would be about 800,000. So, I suppose that a small body could orbit the Earth at a distance comfortqbly inside the limit (say, 1.0 million km) and not have been thrown off by the moon either.


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