Size/Mass of a planet needed in order to have a molten core or a magnetic field?

[jarroe]

How big does a planet have to be in order for it to have a molten core or a magnetic field? Assuming no other large objects were close enough to affect the planet with their own pull or magnetic field. I would imagine the composition/density of the planet would play a factor as well, but do we have any formulas out there that would descibe this. Perhaps we don't have enough samples/data to make an informed decision on this yet?

 

[jarroe]

Age of the planet would factor in as well I am sure?

 

[jedishrfu]

I'm not sure there such a limit but rather how it was formed and what it's made of

See Wikipedia article:

http://en.wikipedia.org/wiki/Planetary_core

 

[SpiffyKavu]

Also take notice of Neptune and Uranus.

http://en.wikipedia.org/wiki/Uranus#Magnetic_field

It is thought that the magnetic field is generated in a liquid layer; not the core.

 

[pmacias]

The size and mass of a planet are important factors in determining whether it will have a molten core or a magnetic field. Generally, a planet needs to be at least the size of Mars (about half the size of Earth) to have a molten core. This is because smaller planets tend to cool faster and solidify, preventing the formation of a molten core.

However, the composition and density of a planet also play a significant role. A planet with a higher density, such as Earth, is more likely to have a molten core than a planet with a lower density, such as Saturn. This is because the higher density allows for more heat and pressure to build up, leading to the melting of the core.

As for magnetic fields, they are primarily generated by the flow of liquid iron in a planet's outer core. Therefore, a planet must have a molten core in order to have a magnetic field. However, the size and composition of a planet can also impact the strength and stability of its magnetic field.

Currently, there is no specific formula that can accurately predict the size and mass needed for a planet to have a molten core or a magnetic field. This is because there are many variables and factors at play, and our understanding of planetary formation and evolution is still evolving. As scientists continue to study and gather data on different planets, we may be able to develop more accurate models and formulas in the future.