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Non-spherical worlds
Topic Started: Sep 9 2009, 09:34 AM (744 Views)
chakka
Zygote
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It's something that has long interested me, the idea of a world totally beyond the norm, a non-spherical world. In part the concept interests because of the common attribute of early man to believe in a "flat" earth and the since ridiculing of that idea; but how ridiculous is it? I realise a disc-shaped planet is out of the question, but are planets stuck within spheres or would, for example, a conal shape be possible, rounded and wide at one end, sharp and pointed at the other?

Basically I've been trying to fully understand how planets form; I've always been interested in speculative biology and long looked to lay ground work on my own ideas, but first need a planet on which to form them. The idea of a structurally unique planet is something I want to look into before simply settling for the standard form :D

From what I can gather planets form during the early stages of a solar system, when groups of dust and rock clump together around denser orbiting structures due to gravity. Over time the densest material percolates to the centre, creating the "core" and laying the groundwork for potential magnetic fields. The reason for a spherical structure is due to gravitational pull, as is its nature, working in all directions and so forming a sphere around the denser material. This all makes sense, although to be honest seems overly simplified, however my thoughts wander in what would happen later on in a planets life once most of the orbiting mass has condensed into satellites or other orbiting bodies. For example, scientists have suggested that the Moon was formed when a large object impacted with the earth, causing material to be thrown out of the gravitational pull and into orbit around the planet, eventually condensing into the moon. That's also fine, but why then did the earth itself become spherical once more? I would imagine its safe to presume that the object that impacted is of equal density to the moon hence it being able to displace such large quantities of material, and the displaced material that didn't escape the gravitational pull would simply fall back into the crate, but still the earth is highly spherical, there's no obvious point of such an impact. Is this purely due to erosion or does gravity actually pull masses together to spread them over an even surface?

In one scenario I can imagine, an event such as progression from a giant star to a dwarf would alter a long established gravitational orbit of a dense planet. Over time this "loops" within a spiralling orbit closer to an inner planet until the two collide; however the velocity of the incoming planet is great enough for it to continue heading along its orbital path, dragging much of the displaced material with it and then at a later stage condensing etc.
This leaves beyond a planet effectively with a chunk taken out of it. Assuming it had already been a dead planet so is solid throughout wouldnt the material prevent gravity from re-forming an actually spherical object? I don't know, perhaps I'm confusing myself...I just wondered if anyone else had any links or ideas on whether non-spherical planets could exist.
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CarrionTrooper
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Maybe non-natural orbital constructs like Ringworlds or Dyson spheres? And could a very dense asteroid belt become a natural ringworld?
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Empyreon
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Are you plausible?

Quote:
 
That's also fine, but why then did the earth itself become spherical once more?


Let's take another look at your example of the moon's formation. The Impact Theory you pointed out is one of the most widely accepted. I found some simulated images of the impact and lunar formation:

Posted Image

Notice that when the impact happens, there is matter thrown everywhere, so you don't just have an orb but a cloud of debris. Also notice that the central mass (shown mostly in green and yellow) doesn't stay in a nice neat circle. This may seem like evidence to support the idea that a planet doesn't have to be a sphere, but it doesn't answer the question of why the Earth reformed into a generally spherical shape.

At an astronomical scale, a planet's mass is fluid, even the substrates that we consider hard (read: rock and landmass) is, in relative terms, a bunch of microscopic specks. So even if it's a "dead planet" as you put it, by which I assume you are saying that it's geologically inert, that doesn't at all mean that it's solid all the way through. Sure, the core may be compressed into something more or less intact, but the outside just wouldn't have the density to maintain any form of shape. Imagine that, at the scales we're talking about, planets are not clumps of "solid' mass, but more like spinning balls of powder. Undisturbed, it coalesces into rotating spheres, but if you bounce another object off of it you're looking at a spray of debris flying away, and the remaining mass wobbling like a water balloon on a trampoline. The water inside represents the planet's remaining mass, the balloon (kind of, but effectively enough) simulates the gravity that holds the mass together, and the trampoline represents the celestial impact. So as the balloon launches into the air it deforms and stretches, taking not just one shape but several. If you were somehow able to suspend the balloon in the air and prevent it from coming back down on the trampoline you would see it continue spinning in the air until it settles down and returns to a stable shape. As far as gravity is concerned, that stable shape is a sphere.

So yeah, this planet may be anything but spherical after such an impact. It would probably even restart geologic activity on the planet, and eventually (if all other criteria are met) even have the potential for life. Unfortunately, by the time that happens the planet would have gone back to its spherical shape. Unless you can figure out a way to make life come about on/in a perpetually churning clump of dirt with a constant rain of meteors...

Another option for a non-spherical planet is in Hal Clement's Mission of Gravity and the accompanying article "Whirligig World."
Edited by Empyreon, Sep 9 2009, 10:46 AM.
Take a look at my exobiology subforum of the planet Nereus!

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food for thought
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chakka
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Wow, thanks for all the information Empyreon. That certainly answers a lot of my questions.

It seems that under gravitational influence alone "spheres" are the only real outcome so I've started wondering whether another force could be used to warp this shape; I know centrifugal force causes earth to "bulge" but could their be anything else that would give the desired effect? Or even could their be some kind of gravitational lock caused by a nearby entity that would allow an otherwise impossible shape?
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sam999
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Adult
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chakka
Sep 9 2009, 09:34 AM
It's something that has long interested me, the idea of a world totally beyond the norm, a non-spherical world. In part the concept interests because of the common attribute of early man to believe in a "flat" earth and the since ridiculing of that idea; but how ridiculous is it? I realise a disc-shaped planet is out of the question, but are planets stuck within spheres or would, for example, a conal shape be possible, rounded and wide at one end, sharp and pointed at the other?

Basically I've been trying to fully understand how planets form; I've always been interested in speculative biology and long looked to lay ground work on my own ideas, but first need a planet on which to form them. The idea of a structurally unique planet is something I want to look into before simply settling for the standard form :D

From what I can gather planets form during the early stages of a solar system, when groups of dust and rock clump together around denser orbiting structures due to gravity. Over time the densest material percolates to the centre, creating the "core" and laying the groundwork for potential magnetic fields. The reason for a spherical structure is due to gravitational pull, as is its nature, working in all directions and so forming a sphere around the denser material. This all makes sense, although to be honest seems overly simplified, however my thoughts wander in what would happen later on in a planets life once most of the orbiting mass has condensed into satellites or other orbiting bodies. For example, scientists have suggested that the Moon was formed when a large object impacted with the earth, causing material to be thrown out of the gravitational pull and into orbit around the planet, eventually condensing into the moon. That's also fine, but why then did the earth itself become spherical once more? I would imagine its safe to presume that the object that impacted is of equal density to the moon hence it being able to displace such large quantities of material, and the displaced material that didn't escape the gravitational pull would simply fall back into the crate, but still the earth is highly spherical, there's no obvious point of such an impact. Is this purely due to erosion or does gravity actually pull masses together to spread them over an even surface?

In one scenario I can imagine, an event such as progression from a giant star to a dwarf would alter a long established gravitational orbit of a dense planet. Over time this "loops" within a spiralling orbit closer to an inner planet until the two collide; however the velocity of the incoming planet is great enough for it to continue heading along its orbital path, dragging much of the displaced material with it and then at a later stage condensing etc.
This leaves beyond a planet effectively with a chunk taken out of it. Assuming it had already been a dead planet so is solid throughout wouldnt the material prevent gravity from re-forming an actually spherical object? I don't know, perhaps I'm confusing myself...I just wondered if anyone else had any links or ideas on whether non-spherical planets could exist.
O.K. have you been playing creatueres? Albia sounds quite like what you are posting of.
I am not suffering from insanaty. I truely enjoy being mad.
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Comeon, thy dragons need YOU! Visit them here please...
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Oceaniis
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Empyreon gave the best exemple! A planet will behave like a fluid, like a water droplet in micro-gravity!

Thinking in make a ring of water in microgravity would be a very dificult task, but I think that would be mush dificult mantain it. Any impact during its formation or gravitacional ressonances would perturbe the balance of forces and the ring would break...
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chakka
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I have not been playing creatures, but I'm also unsure of the comparison xD I guess this looks like a dead end for now, oh well I'll work on some other parts and come back to this in a while
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colddigger
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Joke's over! Love, Parasky
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spheres are the easiest shape to get, you could get something else, but it would take some odd events...
Oh Fine.

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