Today I read a story in the WP relating to the rotation of earths “solid” inner iron core. I looked it up from a different source that confirmed it is solid as opposed to liquid. How can it be so hot and not be molten? Thank you!
Well the core is molten. But not solid. We wouldn’t have volcanic activity if it was solid.
Because despite being really really hot, it’s also really really compressed.
The phase (solid, liquid, or gas) of something is determined by 3 things:
1. The physical properties of the substance
2. The temperature
3. The pressure.
If the pressure is high enough, most things can stay solid, up to pretty ridiculous temperatures.
And it might not be surprising to learn that the core of a planet is under some pretty high pressures.
This also explains why we have 2 cores. The solid inner core, and a liquid outer core. Even though they’re made of the same stuff, because the outer core is under less pressure, it can become a liquid.
It is because the pressure keeps it from actually melting. The materia estate of a substance depends, mainly, of its temperature and its pressure (as inverse of volume). It would depend of other things like density but we could keep this aside for metals and for simplicity.
The high temperature would force molecules or atoms to vibrate more and push neighbours aside, that would break the bonds between neighbours making it easy to flow, thus becoming liquid.
The thing is that the metal core is surrounded by the other layers of molten metal, crust, water and atmosphere. All this mass surrounding the core leads to a pressure in all directions that overcomes the natural tendency of a hot metal under a lower pressure (1 atmosphere, like at sea level). This means that the molecules and atoms will keep acting as a solid metal cause they have not room to expand and flow.
If you were able to instantly drill a hole down to rhe core it would flow upwards and spill around like… a volcano.
I hope this helps.
Thank you all. It seems obvious the way you all explain it.
The pressure and force exerted on an object can change its melting point. The gravitational force and weight on top is immense, thus its a solid.