Why are planets all spherical?

Originally posted by stander

Originally posted by prevenge
not to be a prick or anything.. but why go through all the trouble to ask the question on ATS when you could have just typed it into google.. found out.. then maybe shared your findings on ATS in a thread ABOUT hydrostatic equilibrium?

this is the second time in one week i've seen this question asked..

That's because not all questions regarding the spherical shape of the planets are answered by surfing the net. Here is an example: In 2012, God decided to reshape planet Venus into a cube. How much time would be required for Venus to resume her spherical shape?

(Remember that terrestial planets assumed their spherical shape when they were made of hot, molten rock thereby lacking the hard crust.)

what whaaaaaa?

venus? 2012? god? cube? what are you talking about?

and no.. planets constantly are affected by the gravity of their own mass.. not just when they're soft and molten.
planets are changing shape constantly. through their own gravity and other nearby celestial body's gravity.

it's a constant battle for equilibrium. everything pulling on everything else.

though.. i wouldn't be surprised if centrifugal force played a part in hollowing out some celestial bodies.


but what's this about venus as a cube? what do you mean? are you jsut making that up or did you really read it on the interwebnettubes?

-

The sphere is first and strongest design in Nature

Somewhere out in the primordial soup of the Eagle Nebula.....

A few elemental atoms are drawn together by electromagnetism to form molecules.

Molecular attraction draws in a few more molecules and, given enough time, the molecules coalesce into vapors, clouds of gas and dust.

Dust gravitates to dust and, given enough time, a dusty little blob of matter condenses, its mass increasing because it is now warping space and other little blobs of matter are falling into it. If there's enough homogenous vapor, you know, this condensation could happen really quickly and the blob could get really big, really fast.

Relatively speaking.

Talking about millions or billions of years? HA, I think it only takes about 100 years to assemble a planet at the raw, basic level. Matter coalesces out of star stuff, gains mass, warps space, more stuff falls in due to the warp (we call it Gravity), and the stuff just keeps on falling in, right. But it's a cascade, as the mass increases, its gravity well draws more and more more until...Well, you've got sort of an event horizon.

But not in the sense of a black hole, not quite that energetic... In the sense of planet-building, here's a mass that's sucking up all adjacent dust and debris and comets and asteroids and pallasites (my favorite) and I am telling you this is happening very quickly, a cascade with tremendous kinetic energy.

Mass. Gravity. Pressure. Heat. Time.

Stuff zings in from every conceivable coordinate, converging on the gravity well. Nascent gases huddle thinly on the molten surface. The horizon is pearl black (except that Life is still an eon or two away, so the mod tells me that mentioning a pearl is grossly anachronistic. No pearls. No oysters. No horseradish. No beer).

With this cascade, this bombardment of matter from every coordinate converging on a single point in space, the mass and gravity and pressure and heat generates maybe a little fourth state of matter, a plasma core, hmm? Or perhaps a few mountains of Fe and Ni come slamming into the mix? Eh, we make 'em up as we go along.

That's one way to build a planet, and there are many other ways. In the above idealized description, the mass of cosmic dust & debris attains so much concentrated mass that it eventually attains a sort of dynamic fluid body, with denser elements sinking to the core, its mantle in a perpetual state of metamorphosis, its surface molten (cuz it's a very young planet), so that all its matter is liquified and evenly distributed. No sharp points would exist for long, no Everests — Gravity would equalize everything into a uniform porridge, yes?

That's probably how the Earth started out.... However, the Earth is not a sphere.

Hate to break it to some of ye, but Earth is presently sort of pear-shaped, according to the guys who have gone on-high and eyeballed it. Like a little fat pear, okay, not a tall skinny pear. Apparently, the damned thing also has four corners, but how did the ancients know that?


— Doc Velocity





[edit on 4/13/2009 by Doc Velocity]

Originally posted by prevenge

Originally posted by stander

Originally posted by prevenge
not to be a prick or anything.. but why go through all the trouble to ask the question on ATS when you could have just typed it into google.. found out.. then maybe shared your findings on ATS in a thread ABOUT hydrostatic equilibrium?

this is the second time in one week i've seen this question asked..

That's because not all questions regarding the spherical shape of the planets are answered by surfing the net. Here is an example: In 2012, God decided to reshape planet Venus into a cube. How much time would be required for Venus to resume her spherical shape?

(Remember that terrestial planets assumed their spherical shape when they were made of hot, molten rock thereby lacking the hard crust.)

what whaaaaaa?

venus? 2012? god? cube? what are you talking about?

and no.. planets constantly are affected by the gravity of their own mass.. not just when they're soft and molten.
planets are changing shape constantly. through their own gravity and other nearby celestial body's gravity.

it's a constant battle for equilibrium. everything pulling on everything else.

though.. i wouldn't be surprised if centrifugal force played a part in hollowing out some celestial bodies.


but what's this about venus as a cube? what do you mean? are you jsut making that up or did you really read it on the interwebnettubes?

-

I have not seen for a long time someone like you flanking the condition IF.

Let's try again with a different approach. IF planet Venus changes into a cube, how much time would it take for the planet to resume its spherical shape? Would it take longer than the original shaping or not?

If you are about to argue that planet Venus can't change into a cube, then don't bother to type it in -- you just don't understand the word IF.