Question about planetary gravity

[sethoflagos]

21 minutes ago, Saber said:

you  know   i meant   much  larger displacements  on the  surface of the planet..........22 km's   on  mars  with  6750 km  of  diameter  is  not  even  half a  percent.........i meant  larger   unevennesses .........@  least 10 %  of  the  planets   Diameter.......

Okay, so what would happen to say a waterworld planet tidally-locked to a red dwarf star. Could it be possible for a permanent iceberg to form on the dark side so large that it occupied a substantial proportion of the planets volume? If so, then gravity via buoyancy forces would seek to maintain a substantial elevation difference between the two hemispheres.

As it happens, other issues might come into play such as ice changing phase to a higher density structure at depth could well be a limiting factor.

But going back to Mars, the southern hemisphere is 2-3 km higher in elevation on average than the northern hemisphere for reasons no one seems entirely sure of. This would be consistent with the two hemispheres somehow having different average densities, though there are other possibilities.  

[Genady]

4 hours ago, MigL said:

static, non-charged, Black Holes are perfectly spherical

Aren't static, charged BH perfectly spherical, too?

[MigL]

1 hour ago, Genady said:

Aren't static, charged BH perfectly spherical, too?

I only mentioned 'non-charged' because it is easier to understand.
A charged static BH would similarly have sperical event horizons, but it would have two; an inner and an outer

[Saber]

2 hours ago, sethoflagos said:

Okay, so what would happen to say a waterworld planet tidally-locked to a red dwarf star. Could it be possible for a permanent iceberg to form on the dark side so large that it occupied a substantial proportion of the planets volume? If so, then gravity via buoyancy forces would seek to maintain a substantial elevation difference between the two hemispheres.

As it happens, other issues might come into play such as ice changing phase to a higher density structure at depth could well be a limiting factor.

But going back to Mars, the southern hemisphere is 2-3 km higher in elevation on average than the northern hemisphere for reasons no one seems entirely sure of. This would be consistent with the two hemispheres somehow having different average densities, though there are other possibilities.  

What if a massive  body   say  like a planet  with 1000 Km radius   hit  a rocky  planet  like earth..........the impact would deform it very very drastically.................but after  some time it must  get back to a sphere right ?

[studiot]

12 minutes ago, Saber said:

the impact would deform it very very drastically...

Why ?

A small ball bearing will do more damage to a large billiard ball than another large billiard ball if one hits the other at speed.

If the striking object is large enough it may simply knock the planet to a new orbit, more than damage it.

Before someone jumps in, this is not to say there will not be any damage.

 

 

[sethoflagos]

3 minutes ago, Saber said:

What if a massive  body   say  like a planet  with 1000 Km radius   hit  a rocky  planet  like earth..........the impact would deform it very very drastically.................but after  some time it must  get back to a sphere right ?

That's the most popular theory for what happened to Mars ~4 billion years ago. 

[Saber]

49 minutes ago, studiot said:

Why ?

A small ball bearing will do more damage to a large billiard ball than another large billiard ball if one hits the other at speed.

If the striking object is large enough it may simply knock the planet to a new orbit, more than damage it.

Before someone jumps in, this is not to say there will not be any damage.

 

 

Exactly right......the speed  of an object has  Squared influence on the kinetic energy it carries......but its mass  has  a direct influence....

[Saber]

On 2/5/2023 at 7:18 PM, Genady said:

@Saber, can you think of any other physical effect that could affect the process you've described? (Even if it is purely theoretical and does not occur in practice.)

@ last i  have  some time and  mind  left  to think  about this..........

 

The rotational speed of the planet .........its material  viscosity........also   if  it  has  different  viscositys in  different  depth's &  layers..............its over all gravity force ....

[Genady]

5 minutes ago, Saber said:

@ last i  have  some time and  mind  left  to think  about this..........

 

The rotational speed of the planet .........its material  viscosity........also   if  it  has  different  viscositys in  different  depth's &  layers..............its over all gravity force ....

A hint: 

 

[Saber]

3 minutes ago, Genady said:

A hint: 

 

Its   electro magnetic  field ?    
*   i  dont  know what a  static charged black  hole  is  

[Genady]

5 minutes ago, Saber said:

Its   electro magnetic  field ?    
*   i  dont  know what a  static charged black  hole  is  

Just electric charge. (ignore the BH part)

[joigus]

 

https://www.nature.com/articles/s43247-021-00313-5

Quote

Increased biomass and carbon burial 2 billion years ago triggered mountain building

The geological record following the c. 2.3 billion years old Great Oxidation Event includes evidence for anomalously high burial of organic carbon and the emergence of widespread mountain building. Both carbon burial and orogeny occurred globally over the period 2.1 to 1.8 billion years ago. Prolific cyanobacteria were preserved as peak black shale sedimentation and abundant graphite. In numerous orogens, the exceptionally carbonaceous sediments were strongly deformed by thrusting, folding, and shearing.

[...]

This implies that the high carbon burial played a critical role in reducing frictional strength and lubricating compressive deformation, which allowed crustal thickening to build Palaeoproterozoic mountain belts.

(My emphasis.)

This is what I meant. Graphite is one of the best lubricants, therefore reducing dissipation.

[zapatos]

Quote

 

The  gravity  of the planet  would pull in the  bulged  out part  and  fill in the  concavity and  add the volume of the bulgness to  the   radius of the  planet  equally   and also  the volume of the concavity  would  be equally  reduced  from the radius  .....

I believe the answer is "yes" by definition. If an object cannot assume a nearly round shape then it is not a planet.

Quote

In modern astronomy, there are two primary conceptions of a 'planet'. Disregarding the often inconsistent technical details, they are whether an astronomical body dynamically dominates its region (that is, whether it controls the fate of other smaller bodies in its vicinity) or whether it is in hydrostatic equilibrium (that is, whether it looks round).

https://en.wikipedia.org/wiki/Definition_of_planet

[Saber]

1 hour ago, Genady said:

Just electric charge. (ignore the BH part)

Was  this  the answer  or  a   hint  its self  for the  answer ?

[Genady]

3 hours ago, Saber said:

any other physical effect that could affect the process you've described? (Even if it is purely theoretical and does not occur in practice.)

It is an answer to this ^^^ question. If a planet is electrically charged, all parts will push away from each other, and the planet will tend to be spherical. 

[studiot]

7 minutes ago, Genady said:

It is an answer to this ^^^ question. If a planet is electrically charged, all parts will push away from each other, and the planet will tend to be spherical. 

Why ?

 

Other charged structures are possible as with the girl's hair in the picture or  these large 'molecules'

https://en.wikipedia.org/wiki/Micelle

[joigus]

3 minutes ago, studiot said:

Why ?

 

Other charged structures are possible as with the girl's hair in the picture or  these large 'molecules'

https://en.wikipedia.org/wiki/Micelle

?

Not the case for the Earth, though. It's more of a conductor than a dielectric. And it's one of those cases in which the electrostatic force is orders of magnitude weaker than gravitational force.

[Genady]

6 minutes ago, studiot said:

Other charged structures are possible as with the girl's hair in the picture or  these large 'molecules'

https://en.wikipedia.org/wiki/Micelle

Yes, the resulting shape is not necessarily spherical, because of effects of other factors. The electric charge is a factor that make

16 minutes ago, Genady said:

the planet ... tend to be spherical.

The gravity of the planet is also a factor that tends to make it spherical.

In a situation that the planet is made, say, of a fluid or a thin dust, and it does not rotate, does not experience tides, etc., it will become spherical if electrically charged. Or it will fall apart, if the charge is too strong.

However, material and shape of the parts, tectonic movement, etc., mentioned in the posts above, can make it take other shapes. Thus, "tend."

The same with micelles, whose actual shape depends on other factors as well (my emphasis):

Quote

Micelles are approximately spherical in shape. Other phases, including shapes such as ellipsoids, cylinders, and bilayers, are also possible. The shape and size of a micelle are a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH, and ionic strength.

I've asked about another physical effect that could affect the process described in OP.

Electric charge would affect this process.

Other effects, already mentioned, would too.

[studiot]

That didn't answer my question.

It's a lot more complicated than that

[Genady]

2 minutes ago, studiot said:

That didn't answer my question.

Perhaps, I did not understand the question, then.

 

3 minutes ago, studiot said:

It's a lot more complicated than that

Agree with this. 

It answered mine.

[studiot]

I'm sorry @Genady I was called away in the middle of responding to joigus, to whom my question "why" was addressed.

You seem to have slipped in with a post between posts in our earlier conversation.

 

Anyway I have the time now to explain more so here we go

Firstly let us note that gravitational forces (the original question) always draw matter particles together and that sometimes they are aided by other processes (not necessarily forces) as already discussed.

Set against this,  electric charge can either act to draw particles together or spread them apart, depending upon polarity.
Also if a particle is charged it has an excess of one charge over the other.
So this excess charge will alway be repulsive with charges of the same polarity.

This means that, unlike gravity,  charges of the same polarity will never form an accretion process, drawing more and more such particles together.

So the question arises "What happens when a neutral body of many particles becomes charged "

Well that depends on the shape of that body before it became charged.

The girl's hair forms a perfect example of this.

The hair does not form a sphere with the charge spread over its surface but forms that spiky shape with repulsive forces on each hair balancing out in some respect.

 

Micelles and other accretion bodies such as chelates in solution work like this.

Yet another possibility are the balanced zwitterions.

 

hope this helps

[Genady]

27 minutes ago, studiot said:

I'm sorry @Genady I was called away in the middle of responding to joigus, to whom my question "why" was addressed.

You seem to have slipped in with a post between posts in our earlier conversation.

 

Anyway I have the time now to explain more so here we go

Firstly let us note that gravitational forces (the original question) always draw matter particles together and that sometimes they are aided by other processes (not necessarily forces) as already discussed.

Set against this,  electric charge can either act to draw particles together or spread them apart, depending upon polarity.
Also if a particle is charged it has an excess of one charge over the other.
So this excess charge will alway be repulsive with charges of the same polarity.

This means that, unlike gravity,  charges of the same polarity will never form an accretion process, drawing more and more such particles together.

So the question arises "What happens when a neutral body of many particles becomes charged "

Well that depends on the shape of that body before it became charged.

The girl's hair forms a perfect example of this.

The hair does not form a sphere with the charge spread over its surface but forms that spiky shape with repulsive forces on each hair balancing out in some respect.

 

Micelles and other accretion bodies such as chelates in solution work like this.

Yet another possibility are the balanced zwitterions.

 

hope this helps

Thank you. Yes, this is clear.

I want to point out that I did not ask, which other effect would make the planet spherical.

My question was,

Quote

Without rotation and other affecting bodies, the outcome depends on 3 factors: material of the planet, mass of the planet, and time. Any other?

and then,

Quote

Saber, can you think of any other physical effect that could affect the process you've described? (Even if it is purely theoretical and does not occur in practice.)