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Khairn
12-30-2008, 10:16 AM
For an upcoming campaign I'm creating a setting where the world has a planetary ring (think rings of Saturn). I have a core "in game" concept for the ring that I am happy with, but now I'm working on some of the physical impact that a planetary ring would cause. Here are a few of my thoughts so far.

-primary cause for the creation of the ring is a large meteor that struck near one of the poles of the planets moon disgorging large amounts of debris into space.
-rings are primarily composed of ice and cosmic particles, although a few larger pieces are present
-rings reflect sunlight to a degree, so that during the night a band of light will provide some additional illumination especially during the transitional periods of dawn and dusk
-along the equator the ring will be visible as a thin line in the sky while at the higher latitudes the width of the ring will be more visible

-given a standard axial tilt, the rings will cast a shadow across the higher & lower latitudes during the day resulting in a more dramatic swing in temperature which will create more unstable weather
-greater frequency of meteor showers (and larger impacts) as particles are slowly pulled down to planet

So am I on or off target with the above? Thoughts, suggestions or rambling comments are all welcome.

Steel General
12-30-2008, 10:41 AM
Well I can't answer any of your questions, but it sounds like an interesting idea nonetheless.!

EDG
12-30-2008, 11:24 AM
A polar impact won't be good - any impact big enough to blast stuff into orbit would be big enough to completely wipe out all life on the planet.

You'd be better off (if you're looking for scientific realism) having it as a normal ring system caused by material being broken off from tiny satellites within the planet's roche limit (the distance within which a solid satellite can't hold itself together because of tides).

Another thing to consider is that if your planet is habitable, the rings won't be icy like Saturn's - they'd be dusty like Jupiter's and so wouldn't be as bright (because the temperature in the habitable zone would evaporate the ice away). And also, in the habitable zone the solar tides would cause the ring system to be somewhat unstable - they probably wouldn't last more than a million years or so so they'd be somewhat ephemeral.

Khairn
12-30-2008, 12:47 PM
Thanks for the fast replies!

So something being in place for a million years is ephemeral 'eh? :D

Let me try another angle then. Scientifically speaking ... how would a habitable planet capture enough debris within its roche limit to create a ring(s)? Are we looking at multiple satellites breaking apart, debris gathered from passing comets, part of the moon breaking away when it travelled within the limit, or maybe the solar system passing through some kind of nebula? The amount of solid material in a ring would seem immense (at least to me that is). So with that much material I imagine that some significant event would be needed to give birth to the ring.

With "magic" its easy to come up with something justifiable, but its a little more difficult from a scientific angle.

jfrazierjr
12-30-2008, 01:18 PM
Thanks for the fast replies!

So something being in place for a million years is ephemeral 'eh? :D

Let me try another angle then. Scientifically speaking ... how would a habitable planet capture enough debris within its roche limit to create a ring(s)? Are we looking at multiple satellites breaking apart, debris gathered from passing comets, part of the moon breaking away when it travelled within the limit, or maybe the solar system passing through some kind of nebula? The amount of solid material in a ring would seem immense (at least to me that is). So with that much material I imagine that some significant event would be needed to give birth to the ring.

With "magic" its easy to come up with something justifiable, but its a little more difficult from a scientific angle.

I am no expert here... but I would expect that something hitting a/the moon with a large enough mass would create a huge cloud of debris which might just be enough to create rings, at least for a short time period (short in universe standards). Last I heard, our moon was thought to be the result of a huge body hitting the earth, spewing earth rock into space, and then gravity coalescing into the moon.

EDG
12-30-2008, 01:19 PM
A million years is a blink of an eye, geologically speaking :). Heck, in this case the rings might just last thousands of years - it really depends on whether they're being replenished by material.

Nobody's ever seen a ring system actually form, but we do know that the current rings of Jupiter are maintained by material being blasted off larger (km-scale) minor moons embedded in the rings. Which makes me wonder what came first - the rings or the moonlets - since to sandblast the moonlets you need the smaller debris to be there already, but to produce the debris you need to be blasting it off the moonlets! I'd guess that it starts with an initial impact that breaks up a moonlet, and that debris spreads out and starts the process. Saturn's rings are probably maintained in a similar way, though at least one (the E ring) is maintained by ice particles erupted from Enceladus' active plumes (as the moon orbits Saturn, the erupted material is spread around its orbit, and then can spiral in).

The "standard" way of making rings seems to be to break up some satellites inside the roche limit, and things eventually spread out to become a ring system there. It probably wouldn't form overnight though, probably talking about a few hundred years at least to get a coherent ring system.

You don't actually need that much material to make a ring though - if you put all of Saturn's ring material together you'd probably only get a moon that's a couple of hundred km in diameter.

Talroth
12-30-2008, 02:25 PM
It is possible to get a highly reflective ring formation around an earth like planet, all you really need is a crystallizing substance making up part of a few moons you can bombard with stuff to break it up and throw it off. Something to keep in mind that such an active system is likely to produce a far higher level of 'shooting stars' than earth usually gets. Basically you'll be in an asteroid belt nearly all the time, rather than just a few times a year.

But like EDG said, any ring formation around a planet the size of earth is likely to be rather unstable, and prone to collapse and gaps. Keeping a "Grand Ring" like we see around Saturn would be unlikely, but smaller thinner rings found on other gas giants. Interestingly enough I just came across a wikipedia entry on Rings of Rhea. Hopefully we'll see newer probes set up to study things like that in more detail before we all die.

EDG
12-31-2008, 05:03 AM
Bright or reflective rocky material (as opposed to icy, which you can get in the outer stellar system) is hard to come by... most rock is naturally dark and not very reflective (low albedo). Then again our own moon only reflects about 12% of the light that hits it, and look how bright that is - the reflectivity of icy rings like those of Saturn is way higher than that (30 to 60%), but the main dust ring of Jupiter and those of Uranus are only around 1%. (refs: http://nssdc.gsfc.nasa.gov/planetary/planetfact.html )

Also, you'd really only get more meteors streaking in at the equatorial plane of the planet, under the rings as the particles in them slowly spiral in. Nearer the poles, you won't get many more meteors than what you'd naturally expect from the planet passing through the usual cometary debris in its orbit.

Nerdling
12-31-2008, 05:40 PM
For an upcoming campaign I'm creating a setting where the world has a planetary ring (think rings of Saturn). I have a core "in game" concept for the ring that I am happy with, but now I'm working on some of the physical impact that a planetary ring would cause. Here are a few of my thoughts so far.

-primary cause for the creation of the ring is a large meteor that struck near one of the poles of the planets moon disgorging large amounts of debris into space.
-rings are primarily composed of ice and cosmic particles, although a few larger pieces are present
-rings reflect sunlight to a degree, so that during the night a band of light will provide some additional illumination especially during the transitional periods of dawn and dusk
-along the equator the ring will be visible as a thin line in the sky while at the higher latitudes the width of the ring will be more visible

-given a standard axial tilt, the rings will cast a shadow across the higher & lower latitudes during the day resulting in a more dramatic swing in temperature which will create more unstable weather
-greater frequency of meteor showers (and larger impacts) as particles are slowly pulled down to planet


I am taking the existence and stability of the rings for granted. You can figure out how it keeps together.

First, the presence of a ring system indicates that there is no moon, because a moon's gravitational pull would pull in any debris within it's orbit, which is where the rings would be.

Without a moon, and with a ring system, the amount of impacts from space crap would be staggering, causing a more or less permanent winter from all the dust in the air (that's an interesting idea for a campaign setting...). Civilization will most likely be concentrated underground, where it is safe from the constant bombardment of the falling space debris, with the surface world being a dangerous, frozen world where only the brave dare enter venture.

If the ring is perfectly in line with the plane of the planet's orbit around the sun (not the axis., as indicated in your second point, instead of a thin band in the sky, the area north/south from the equator for about 2-3 miles would be in a permanent state of total solar eclipse (sort of a desolate, barren darkness across the center of the planet, that's a cool campaign idea as well!).

On your point about the axial tilt causing the rings to cast a shadow. During each day, there would be two periods of night lasting about 1-3 minutes depending, on one's position on the planet, when the sun crosses behind the rings.

Here's a idea of the world as I see it. The rings were created during a time when civilizations were present on the surface, the planet would be covered in ruins buried in ice that were abandoned as civilization fled the surface, a great place for a party of adventurers. Surface flora and fauna will have adapted to the drastic environmental changes. Burrowing creatures will have survived because they can take shelter underground and will have taken a role in many ecological niches that were left empty. Everything will be adapted to survive in sub-freezing temperatures (Layers of insulating hair/fat, etc.)

I really want to go on, but I probably should quit while I'm ahead.

EDG
12-31-2008, 06:02 PM
First, the presence of a ring system indicates that there is no moon, because a moon's gravitational pull would pull in any debris within it's orbit, which is where the rings would be.

Not necessarily. Rings can only extend out to about 2.5 planetary radii, so if a moon is beyond that then it won't really pull anything out at all. Unless they're literally right next to the rings, the most other moons will do is create gaps and other structures due to orbital resonances.


Without a moon, and with a ring system, the amount of impacts from space crap would be staggering, causing a more or less permanent winter from all the dust in the air (that's an interesting idea for a campaign setting...). Civilization will most likely be concentrated underground, where it is safe from the constant bombardment of the falling space debris, with the surface world being a dangerous, frozen world where only the brave dare enter venture.

Having a ring system doesn't mean that you get a constant rain of rocks falling from the sky - you'd just have dust slowly spiralling in and all of it would burn up in the atmosphere because it's just not big enough to survive the fall to the ground.



If the ring is perfectly in line with the plane of the planet's orbit around the sun (not the axis., as indicated in your second point, instead of a thin band in the sky, the area north/south from the equator for about 2-3 miles would be in a permanent state of total solar eclipse (sort of a desolate, barren darkness across the center of the planet, that's a cool campaign idea as well!).

It won't be in line with the planet's orbital plane - the orbital dynamics just doesn't work like that. Tidal forces will very rapidly pull anything on an inclined orbit close to the planet into its equatorial plane. What you *can* have though is a tilted planet, so that the rings around it that are aligned with the equator change their orientation relative to the sun. This is what happens with Saturn over the course of its orbit aroudn the sun, which is why sometimes the rings are edge-on as seen from the sun, and other times they're inclined by about 26 degrees (the planet's axial tilt) and thus cast huge bands of shadow on the hemisphere underneath them.



On your point about the axial tilt causing the rings to cast a shadow. During each day, there would be two periods of night lasting about 1-3 minutes depending, on one's position on the planet, when the sun crosses behind the rings.

I suspect it'd last longer than that, but it depends on the planet's rotation period. Also it would depend on whether the rings were thick enough to actually block out all the light or just make the sun flicker or reduce its brightness somewhat as it passes behind them.



Here's a idea of the world as I see it. The rings were created during a time when civilizations were present on the surface, the planet would be covered in ruins buried in ice that were abandoned as civilization fled the surface, a great place for a party of adventurers. Surface flora and fauna will have adapted to the drastic environmental changes. Burrowing creatures will have survived because they can take shelter underground and will have taken a role in many ecological niches that were left empty. Everything will be adapted to survive in sub-freezing temperatures (Layers of insulating hair/fat, etc.)

You're basically just describing a post-large impact scenario there - another way to do the same thing woudl be to keep the rings but just not have them be the cause of the disaster - instead have a large (km-scale) asteroid smack into the planet and cause massive environmental disruption, but not wipe out all life. Your world would then be in the "nuclear winter" stage after the impact when the temperatures have dropped.

Nerdling
01-02-2009, 03:16 AM
I concede. Victory is yours...

EDG
01-02-2009, 04:38 AM
Nerdling - your concept can still work, it just means shifting your environmental influence from the rings to a single asteroid impact on the planet - otherwise everything else can stay pretty much the same.