# Thread: How big can a solid object be?

1. ## How big can a solid object be?

Just a physics/astronomy question from a simpleton. But a curious simpleton nonetheless.

The general rule of thumb seems to be that larger objects, on an astronomical scale, will have less and less mass/density. AFAIK it is our own puny little planet which is the largest rock solid object we know of. The big planets in our solar system are all gas giants, and the even larger ones we've found in other solar systems always have less mass than Jupiter.
Is there some kind of threshold where rocky/solid objects just can't get bigger? I am excluding black holes since at that point they just don't give a shit and live by their own rules.

2. Isn't most of our planet liquid?

(in the form of molten, not the oceans)

3. Originally Posted by Rixis
Isn't most of our planet liquid?

(in the form of molten, not the oceans)
Think so, the mantle is huge. We go solid-semisolid-liquid-solid from inside to out if I remember.

No idea. I'm pretty sure there are bigger rocky planets out there than earth. Your problem comes with gravity from the nearby star, so positioning is everything in terms of how much coagulates in certain locations.

Edit: You'd have to think about densities as well. Certain rocks weigh more than others and so on so forth.

http://en.wikipedia.org/wiki/Terrestrial_planet <- might find this interesting reading.

4. Biggest possible solid object i know of is Mercury, until we find out of Mars`s core is solid or not.
Though i bet its bigger rock planets out there, just need to find em.

5. Originally Posted by MerinPally
Think so, the mantle is huge. We go solid-semisolid-liquid-solid from inside to out if I remember.

No idea. I'm pretty sure there are bigger rocky planets out there than earth. Your problem comes with gravity from the nearby star, so positioning is everything in terms of how much coagulates in certain locations.

Edit: You'd have to think about densities as well. Certain rocks weigh more than others and so on so forth.

http://en.wikipedia.org/wiki/Terrestrial_planet <- might find this interesting reading.
That's something that has always confused me, How did they decide what our earth is like inside? I've seen so many cut-away pictures and I just don't see how it's even remotely possible they could have any inclination what the earth is actually like on the inside, considering if relation the lowest/deepest points anyone has reached really isn't that far.

6. I bet there is going to be at least one 'check in my pants'-joke so i'm calling it out in this post to ruin somebodys' fun.

On topic though; mercury is probably the biggest fully solid rock we know of. Don't quote me on this though, i'm not an astrologist.

Chances are there are many more planets fully solid but it's hard to tell becuase of the distance between the next solar system and ours.

7. Originally Posted by Gobra
That's something that has always confused me, How did they decide what our earth is like inside? I've seen so many cut-away pictures and I just don't see how it's even remotely possible they could have any inclination what the earth is actually like on the inside, considering if relation the lowest/deepest points anyone has reached really isn't that far.
Well, the distance from the very bottom of the Mariana Trench to the mantle is really not all that far. We've not drilled down but there have been plans to for a longgggg time. It's feasible, just extremely expensive and dangerous so it's not been done.

Don't quote me on this, I'm not certain how they found out, but if I had to take a guess it'd be usage of sound waves and then general understanding of physics. Once you know the size of your sphere and then various densities of what's on the outside, you can use maths to calculate phase changes (Solids liquids and gases) and how pressure will equate to temperature increases and so on. Sound travels with varying speeds through different states so using something like the Clausius Clapeyron equation and numbers obtained through other calculations, you should be able to work out what you're looking at.

I'm only a chemist though, no geologist or physicist so that's all wild speculation. Will google it later after I watch this WCS World Championship match

Edit: Was thinking things like this following graph. I've studied them at university to understand Thermodynamics and that sorta stuff. If you know how your sample would react and then rough quantities of it, pressure etc, you can get a graph such as this.

8. Originally Posted by Gobra
That's something that has always confused me, How did they decide what our earth is like inside? I've seen so many cut-away pictures and I just don't see how it's even remotely possible they could have any inclination what the earth is actually like on the inside, considering if relation the lowest/deepest points anyone has reached really isn't that far.
If you squeeze a tube of toothpaste, toothpaste comes out, you see what's inside without digging.

Volcanoes up chuck a load of lava, gives you hints.

As well as various sciences regarding pressures, melting points, history/evolution of land mass (mountains, earthquakes and stuff).

9. Originally Posted by Itira
Don't quote me on this though, i'm not an astrologist.
Sorry, you have given me little choice

That's a quality quote, priceless

10. Originally Posted by Rixis
Isn't most of our planet liquid?

(in the form of molten, not the oceans)
Most of hte planets SURFACE is liquid.

- - - Updated - - -

Originally Posted by Lazy Gecko
Just a physics/astronomy question from a simpleton. But a curious simpleton nonetheless.

The general rule of thumb seems to be that larger objects, on an astronomical scale, will have less and less mass/density. AFAIK it is our own puny little planet which is the largest rock solid object we know of. The big planets in our solar system are all gas giants, and the even larger ones we've found in other solar systems always have less mass than Jupiter.
Is there some kind of threshold where rocky/solid objects just can't get bigger? I am excluding black holes since at that point they just don't give a shit and live by their own rules.

I sincerely recommend this book to you, if you are interested in this subject. It might be one of the best books ever written.

11. I know, but the surface constitutes very little of the planet as a whole. The reference to the oceans was my pointing out I wasn't being a derp and referring only to the oceans.

12. Originally Posted by Noomz
Most of hte planets SURFACE is liquid.g
LOL. And you just told someone else to read a book.

13. Originally Posted by Noomz
Most of hte planets SURFACE is liquid.
He already said he didn't mean the oceans.

14. The outer core and mantle are thought to be liquid. The inner core solid, 80% iron.

15. http://en.wikipedia.org/wiki/Chandrasekar_limit

Anything more massive than this, will collapse into a black hole. I believe there is an equation that can tell you the dimensions of the object as well.

Right now the largest "solid" structure in the universe would be Neutron stars, as normal stars are gas and plasma, a neutron star is just pure neutrons, and is essentially just one solid ball of neutrons (a teaspoon = Everest in mass).

16. Originally Posted by Itira
I bet there is going to be at least one 'check in my pants'-joke so i'm calling it out in this post to ruin somebodys' fun.

On topic though; mercury is probably the biggest fully solid rock we know of. Don't quote me on this though, i'm not an astrologist.

Chances are there are many more planets fully solid but it's hard to tell becuase of the distance between the next solar system and ours.
Beat me to the punch line.

But yes, Mercury is probably the current largest fully solid rock we know of, and like others say we still have other solar systems then ours and mars ect to still check to really find out that answer.

17. I don't understand your question.

Solid is a term used to describe a state of matter.

The crust of the earth is solid but it's mantle and core are liquids. The gravity of the earth is large enough to cause a force of pressure which is enough to liquefy the rock and iron below the crust. And this isn't even considering the fact that we have an atmosphere and water which can't be classed as solids.

So do mean how large can an object be before it's gravity causes a change in the state of matter from a solid to a liquid?
No fucking idea because it's too vague of a question. Known elements have different masses with a wide array of properties which react very differently to pressure.

So if we narrowed it to a single element and asked how big can a ball of iron be before it's core states to liquify under the force of it's own gravity?
No idea. I wouldn't know where to begin with the maths and I'm not even sure it's possible to calculate as we don't fully understand the force of gravity.

18. I'm gonna say a Neutron Star. But that depends on what we count as solid. Mercury got a molten core, do we count that as solid? Otherwise a Neutron Star is the biggest

Quote from Wikipedia: "A typical neutron star has a mass between about 1.4 and 3.2 solar masses (see Chandrasekhar Limit), with a corresponding radius of about 12 km. In contrast, the Sun's radius is about 60,000 times that."

19. Originally Posted by Lazy Gecko
I am excluding black holes since at that point they just don't give a shit and live by their own rules.
pfahahaaa great sentence

on your question, no idea, probably huge ass big

20. People are ignoring my neutron stars

Thats literally about as solid as you can get before it collapses, the thing is, an atom it mostly empty space, if a hydrogen atom was to scale, and the proton at the nucleus was about the size of your monitor, the electron, would be 22 miles away about. Thats a lot of empty space :P

Neutron stars dont have that space its all just crammed into an area about the size of new york city.

edit: I made this before amirila posted, thank you for seeing my post <3

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