View Full Version : world building & astronomy

10-06-2004, 12:18 PM
I was playing around with world building ideas for a WIP lately and started imagining what the earth would be like if our moon were a ring instead. Two immediate thoughts came to me:

If the moon had always been a ring, then I wondered what the effect would be on earth's climate, tides, etc.

On the other hand, if the moon were suddenly and violently shattered into pieces that eventually formed into a ring, what kind of impact would such a catastrophe have on life on earth?

Any astronomy buffs out there have some ideas?

10-06-2004, 05:58 PM
Here's a good place to ask this question:

sff.net.worldbuilding (http://webnews.sff.net/read?cmd=xover&group=sff.writing.world-building&from=-10)

What I do know is that the moon was created by a catastrophe. A huge object struck the Earth. The ejected material fell together to make the moon.

I don't know what different conditions would have been needed to create a ring instead of a solid body.

Writing Again
10-06-2004, 08:41 PM
There are at least six theories to account for the moon.

The idea the earth and moon formed at the same time from the same materials.

The idea that the moon just spun off from the face of the earth one day and hung around to watch the look on its face.

The idea that the moon just sort of evolved from a bunch of dust floating around that had nothing better to do than form a big ball.

The idea that it was a passing planet the earth's gravity captured.

The idea that a mars sized planet slapped the earth upside its head and knocked the moon off its left cheek.

The idea that God decided the moon would be a good thing to have and hung it out like a Christmas ornament.

The problem is that every one of these ideas has a flaw in it somewhere. The proponant of each happily points out the flaws of everyone else's theory and blithely skips over the flaws in their own.

But I guess anything is better than admitting there is something that we just do not know.

I personally think it is a big moth egg waiting to hatch.

10-06-2004, 11:09 PM
On the other hand, if the moon were suddenly and violently shattered into pieces that eventually formed into a ring, what kind of impact would such a catastrophe have on life on earth?
For story possibilities, I like this one. I assume you are creating a world rather than an alternate history for Earth.

So, when does this event occur? In the present or past? If in the past, were the ancestors of your current peoples sufficiently evolved to record the event in some way -- and would they have survived at all?

I would create an 'idea tree' with these kinds of thoughts branching off from the various ideas, see where they lead you.

Lots of possibilities. Have fun!

10-07-2004, 04:18 AM
If the moon had always been a ring, then I wondered what the effect would be on earth's climate, tides, etc. If the moon was always a ring, there'd be no tides. And, without tides ... LOTS of things change.

10-07-2004, 05:39 AM
Absolutely. Life forms on Earth would be drastically different as well.

10-07-2004, 07:42 AM
Thanks for the comments, guys.

To put this in a little more context:
I had hoped to use this idea in a fantasy story I am working on. I prefer, however, to try and develope a scientifically plausible explanation to all the elements (magic, monsters, etc.) of my fantasy stories. That way, I can present the scientific explanation alongside the mythic explanation and let the reader decide which one they prefer. This idea of having a ring rather than a moon would be just such an element.

In response to some of the questions that were raised:

If the ring had always been a ring, then I agree that life probably could have evolved quite differently. But I wonder if having a ring instead of a moon would necessarily preclude the possibility of humanoids evolving. My guess would be no.

If, on the other hand, the ring had been created from the remnants of a destroyed moon, I assume the destruction on the planet's surface would be so catastrophic that it would take eons for life to recover fully. Thus, I am leaning towards setting the story with the ring in place and, as far as humans are concerened, it has always been that way.

One last thought:
I wonder what it would look like from the planet's surface. We always see pictures of rings from a distance. Can you imagine looking up and seeing one stretch up off the horizon, day or night?

10-07-2004, 09:35 PM
I wonder what it would look like from the planet's surface
That would be pretty neat, all right. I'd try to work into your story how it would look from different latitudes. At the equator, it would be edge-on, but the further north or south you go, the more of the ring structure you'd see. This could add to the story, such as a northern dweller travelling to equatorial regions and missing the splendour in the sky he/she took for granted, or an equatorial person who has never travelled, taking a first trip south and suddenly seeing the true nature of the rings, stuff like that.

Good luck with it, it sure sounds like it'll be a fun read.

10-08-2004, 02:46 AM
This site (http://www.the-planet-saturn.com/saturns-rings-pictures.html) claims that the earth is not large enough to have rings. Does anyone have any idea if that's true? :shrug

10-08-2004, 03:25 AM
Interesting. I think that it might well be difficult for rings to form around the Earth for the reasons stated (gravity). Particles would have to be in a pretty exact orbit to be captured by a gravitational field the strength of Earth's this close to the Sun. However, the Sun could not so easily pull matter out of Earth orbit, otherwise the moon would have been 'sucked away' long ago. Therefore, a ring system could form and be stable if the moon were to disintegrate.

Perhaps in Mukaden's story idea, this could have happened long before sentience arose on his world and therefore as far as the intelligent inhabitants are concerned, the ring has always been there.

10-08-2004, 04:01 AM
The smaller planets do not have strong enough gravity to keep a ring system. The planets like Mercury, Venus, Earth and Mars will also lose such a ring system because the MUCH stronger gravitational forces of the Sun will pull the ring particles away from these planets. (These planets are much closer to the Sun than Saturn)[this quote is from the site recommended above; emphasis is mine]

However, the Sun could not so easily pull matter out of Earth orbit, otherwise the moon would have been 'sucked away' long ago. Therefore, a ring system could form and be stable if the moon were to disintegrate.Chunky, I believe the situation with Earth and its moon Luna is this: Luna is, as far as moons go in our solar system, a giant, in proportion to the planet it orbits. Check out the size of the moons of Mars in relation to Mars itself, and there's no question that the moons of Jupiter and Saturn are tiny compared to their host planets. Earth and Luna are nearly a binary pair; the gravitational attraction of two such large bodies is unique in our solar system. That is why the Sun can't pull Luna away from its orbit about Earth.

However, in the case of a ring, should such a thing form by whatever reason, the individual particles in it are tiny, and there is no longer the mutual gravitational attraction between them and Earth. And then, the Sun's gravitational pull comes into play. This is probably why there are no significant bodies in the Earth-Sun L4 and L5 Lagrangian points (sometimes called Trojan points because of the collections of asteroids named for Trojan heros that do exist at the Jupiter-Sun L4 and L5 Lagrangian points).

I suppose it might be possible for rings to exist about an Earth-sized planet in an orbit out by say, Neptune or Uranus, but of course, there, life as we know it couldn't exist...too danged cold.

All that said, I think it'd be fun to tell a story about the destruction of Luna and the formation of rings, followed by the slow dissolution of them.

10-08-2004, 04:21 AM
Good info, Pthom.

So, then you could consider giving your Earth size planet a great enough density to hold a ring, and subsequently higher surface gravity, and the attendant differences that would make in your ecosphere. Your animals would have to have hearts like jackhammers and blood vessels that could withstand incredible pressures. I wonder just how far you'd have to jack up the planet's gravitational pull to make a permanent ring system possible, and how big such a rocky Earth-like world would have to be, and just how much further out from the star it would orbit.

I have a feeling if you could find that balance between all these things and come up with a viable planet, it would be at the very extreme of being able to support life, if at all. Your suggestion of a world where the ring used to be a moon and is slowly being 'eaten away' by gravitational forces would probably be the best option. The time scale involved for the ring to disappear should allow for the rise of a pretty complex society while the ring is still a distinct structure.

10-08-2004, 05:04 AM
That's why hard sci-fi is so fascinating.

10-08-2004, 08:05 AM
Yep :grin

Kempo Kid
10-09-2004, 07:14 AM
This is a good book on this topic (although I can't remember if they cover rings or not). What if the Moon didn't Exist? by Neil F Comins. Covers all sorts of hypothetical situations like that.

10-10-2004, 06:26 AM
The only other contender in the Solar System for a binary pair is Pluto-Charon, and they're both so small they hardly count.

On a related topic, SF often has Earth-type planets with two or more moons. It's always seemed to me that, if the moons were big enough to be significant, the competing tidal forces would have such a devastating effect that the development of life would be unlikely. But maybe that would depend on their orbits.

As far as the rings are concerned, the points given seem quite convincing. It can hardly be a coincidence that most of the gas-giants have rings and none of the rocky planets do.

10-10-2004, 07:29 PM
Just as an aside to Writing Again: My astronomy professor had us grade all those theories (except the God-Christmas tree ornament theory oddly enough, because I was at a church sponsered school) against the facts we knew about the moon, ie. the mineral components of the moon, size, closesness to the earth, etc. He was very careful to stress that they were all theories, but I think we came to the conclusion that the most likely theory consisted of a large object striking the earth somewhat early on in both objects formative process.

General aside: I was just thinking of Asimov's Foundation and the latter books which include a search for Earth. The characters are discussing unique traits about Earth, and one is the relative size of the moon, and the lack of other moons.