I was thinking of adding rings to my planet and I wanted to give them a proper origin, so I thought about getting rid of the moon closest to the planet since I would still have one and it could make for some really cool catastrophe or influence in old cultures (something like an ancestral phoenix God present as a moon, reborn as a "sky-belt").

I've documented myself on the topic. From what I've learnt the Moon, here on Earth, has a lot of influence beyond just the oceanic tides: It brightens the nights, keeps the planet from rotating too fast (what protects us from shorter days and very fast winds) and balancing it's rotation so our axial tilt doesn't go nuts (protecting us from a lack of seasons and the possibility of solar radiation coming in right through what would become sun-facing poles).

Once knowing how much of an impact the existence of these natural satellites has on a planet I'd like to ask: How much of an impact would losing a moon have on my system? I'd like to know if the ring replacing the moon will have much impact on the planet. For example, if it doesn't have much of a difference in going from two to a single moon.

Notice since most of the moon's mass would still be there in the ring (what (maybe?) would that mean there's less of an impact due to the even gravitational pull)

Some useful information:

  • Planet's mass is 1.3 that of Earth.
  • Planet's radius is 1.1 that of Earth.
  • The destroyed Moon's mass is about half of Earth's Moon.
  • The destroyed Moon orbited the closest it could to the Roche Limit.
  • The furthest (now only moon) is our Moon's mass approx.
  • The furthest moon radius is 1.2 that of our Moon.
  • The furthest moon orbits 400 000 km above its planet's surface with very little eccentricity.

I don't know about the utility this may have for an answer but for the moon's destruction the plan was to front crash a big enough asteroid so its velocity lowered enough to enter the Roche limit, letting gravity work its magic.

  • $\begingroup$ A moon breaking up into a ring system (whether first being impacted by another object or not) by entering a planet's Roche limit would rain meteors down in an unimaginable mass extinction level event. Complex life would not survive such an event, and it would take at least tens of millions -- probably billions -- of years for life to re-evolve beyond simple single-celled organisms again. To quote DMs of the past: "Rocks fall. Everyone dies." $\endgroup$
    – Ghedipunk
    Aug 1, 2018 at 22:14
  • $\begingroup$ For an example of what this would be like: en.wikipedia.org/wiki/Late_Heavy_Bombardment $\endgroup$
    – Ghedipunk
    Aug 1, 2018 at 22:16
  • $\begingroup$ I've been playing with orbital simulators and have been unable to get two significant moons in a stable configuration. Significant: min 1/2 degree apparent visual diameter. If the moons are big enough to not be points, they affect eachother and either one exits, or one strikes the primary. $\endgroup$ Aug 2, 2018 at 0:42
  • $\begingroup$ That planet's Roche Limit is going to be really close. Tides would be severe. $\endgroup$
    – RonJohn
    Aug 2, 2018 at 3:05

1 Answer 1


Assuming the moon falling on the planet didn't wipe out all life on it (it would, but let's assume it didn't), I'm no expert, but it seems to me that the loss of a moon would result in...

  • Changes to tides, resulting in the deaths of most ocean fish
  • Changes to wind patterns, causing massive storms immediately, but in the long term it would just mean different wind patterns and different storms
  • Changes in the magnetic component in the environment, confusing (and maybe causing extinction of) some birds and bugs
  • Changes to the orbit of the other moon which was farther away, which would mean more tidal changes, etc.
  • More meteors hitting the planet in general, because the moon acts as a natural barrier
  • Changes to the wobble of the planet in its orbit, perhaps changing the planet's orbit entirely, meaning a significant change to the climate and seasons, which could potentially have a very significant impact on the livability of the planet as a whole (or maybe not)
  • Widespread volcanic eruptions in the short term, due to the sudden change in gravity affecting the planet's crust

The resulting ring would mean:

  • Frequent meteor showers under the ring for a very long time
  • Meteor showers under the ring whenever anything passes through the ring and bumps into some rocks there
  • depending on your ring, probably a corresponding ring of craters on the planet's surface, which would be much wider than the ring itself because of the tilt of the planet's axis relative to the tilt of the ring.
  • depending on the chemical composition of the inside of your moon (which is now the ring), perhaps some really cool light shows in the sky when the ring is between the observer and the sun. If the ring is made of a translucent material, it could cause light to focus in some areas, making it very dangerous to be in those places or look at the ring when the sun is behind it (like at the bottom of a pool), but causing giant rainbows to randomly shine different colors of light onto the parts of the surface of the planet (like the Pink Floyd poster). If it's made of a magnetic material, you could get an aurora. If it's made of something else, then you might just get a shadow.

As I've been writing, I've been trying to think of a way you could blow up your moon into a ring without simultaneously killing all life on your planet. I'm thinking that a very big asteroid could pass by close to your planet without hitting it, and knock your moon away from your planet, disintegrating it in the process. The debris trail from this asteroid and the resulting moon-debris would cause significant damage to your planet, but it might not be enough to totally wipe it out, (especially if you find as a result of this that your moon was porous and mostly hollow). Alternatively, if the moon was hit towards your planet, it could pass temporarily within the roche limit and then slingshot much further away than it was before, disintegrating the moon over the course of several passes, and maybe mitigating the severity of the destruction on the planet slightly. In any case, the changes I listed would still happen, I think.


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