So, I'm creating a jungle world that orbits a K class star (aka orange dwarf star), and is the second planet in the system. Now, I have the planet having two moons: one that is similar to our moon (although a bit smaller) and a second moon that is a good bit smaller than that moon. Also, the planet has rings similar to the rings of Saturn/Jupiter.

Now, while countless sources have stated that a two moon system would play havoc on a planet's tidal system, this is taking into account of the amount of ocean that a planet has: it being the same amount as Earth's. (sources that say a two moon system would play havoc on a planet's tidal system and they're the ones that also say that the two moons would eventually collide:


According to this source, http://planetstar.wikia.com/wiki/Forest_planet , jungle and forest planets would hardly have any hurricanes due to their oceans beings not so deep or vast. So, that helps my world a good bit in preventing tidal systems from being extremely dangerous. Plus, the world is only approximately 40% ocean. It still is tectonically active, which helps in creating volcanic eruptions in putting carbon dioxide back into the atmosphere (what with all of the plants on the planet).

Now, while there is a good bit of light coming down to the planet due to the two moons and planetary rings, there would be areas of the planet where hardly any light reaches the forest floor. This is similar to certain rain forests here on Earth (i.e. the Amazon rain forest).

One thing that I looked at was how the planet's gravity would be affected by a two moon system. I figure that it would have a lighter gravity than Earth's, but this would be alright as the two moon's pulling on the planet would probably make it closer to ours, although I'm still researching this, so I could be wrong.

Another factor that I'm looking at is if the planet is a super-Earth. I figure this would also help stabilize tides and make things easier for the dominant species of fox-like caninoids to evolve on the planet.

The thing that I'm worried about is that all of my sources say that the two moons would collide. I've searched and searched but I can't seem to find anything that says how to keep them from colliding with one another.

So basically I'm asking: have I done my homework? Have I forgotten anything? Do I need to look at other sources? What things have I not taken into account when designing this world?

This basically boils down to one question: is this planet even possible?

  • $\begingroup$ See also worldbuilding.stackexchange.com/questions/78263/… $\endgroup$
    – JDługosz
    Commented May 2, 2017 at 0:54
  • $\begingroup$ «countless sources have stated that a two moon system would play havoc» that's not what's posted here in WB! You may want to post a new answer to that question if you have information otherwise (and the link your statement above to that post). $\endgroup$
    – JDługosz
    Commented May 2, 2017 at 0:58
  • $\begingroup$ See Can you add a mini moon to Earth?. A larger planet makes things easier, though. $\endgroup$
    – JDługosz
    Commented May 2, 2017 at 1:02
  • 1
    $\begingroup$ Oh, Welcome to Worldbuilding! $\endgroup$
    – JDługosz
    Commented May 2, 2017 at 1:05
  • 1
    $\begingroup$ Just my opinion here, First you have apparently done a lot of Technical Background Work. So that is ok, did it need to be that complete? Who knows. BUT your question is not what this Q/A tends to want to deal with. This Q/A would prefer to answer more concrete questions like what would be the length of day. What would be the highest a tree could grow etc. Your question seems to be asking the Community to do a Review of your work. My opinion is that you should ask a question(s) that you think you may need help on vs asking for your work to be reviewed. You can enter into a more interactive ... $\endgroup$ Commented May 2, 2017 at 1:33

1 Answer 1


Gravity of moon as felt on earth: $$ a_{moon->earth} = \gamma \frac{ m_{moon} 1s^2}{c^2} = 0.0005 \frac{m}{s^2} $$

I don't think that will seriously affect your gravity.

Mars has two moons and they don't seem to have collided. Jupiter has at least four (+ lots of big moon-like junk). Of course you might need to add certain additional constraints to your satellite systems such as tidal locking, small integer harmonics as satellite periods and discrete possible orbits, but there should be no reason for your satellites to collide.

I'd check the mechanics of Galilean moons for details on how to design such system.

Adding rings might actually be problematic. That implies either one more moon which was blown apart or some gravitational disturbances. I am not sure what is minimal planet size/mass which allows for rings to form without them being cleared (ie. sucked) into the planet's atmosphere.

  • $\begingroup$ Interesting. Basically, it would be possible that a third moon was destroyed and created the rings. But if I'm not mistaken, the two moons' gravity would help keep the rings in place. In terms of the tidal locking, that's actually a good call. I'm unsure of satellite periods as well as the discrete possible orbits. Could you elaborate on those please? $\endgroup$
    – SCPilot
    Commented May 3, 2017 at 0:27
  • $\begingroup$ I have no idea how would a cloud of junk be affected by moon rotating in it, and my math is definitely not good enough to solve such problems. Maybe a simple computer simulation could be written to see what happens in different cases. $\endgroup$
    – vguberinic
    Commented May 3, 2017 at 1:18
  • $\begingroup$ I don't quite understand your notation, which seems nonstandard. What are $\gamma$ and $c$? $\endgroup$
    – HDE 226868
    Commented May 3, 2017 at 19:37
  • $\begingroup$ $\gamma$ is Newton's gravitational constant and $c$ is speed of light. I have assumed that distance Earth to Moon is one light second. $\endgroup$
    – vguberinic
    Commented May 3, 2017 at 20:54

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