<p><a href="https://astronomy.stackexchange.com/a/22964/9527">This answer</a> makes the assumption that the ratio between the radius of a planet and the radius of its core is roughly constant shortly after planetary formation. Why should this be the case? Do we know why, when a planet forms, it ends up with half of its radius being core?</p>

CC BY-SA 4.0
2020-03-24T09:52:04.957Z
Isn't this just based on assuming the same mix of heavy core-forming elements and lighter mantle/crust forming elements? Take any mass of the mix, turn it into a sphere and have a core form, and the ratio should be the same.
Anders Sandberg
CC BY-SA 4.0
2020-03-24T17:11:21.930Z
I don't think your linked question/answer makes that assumption for any other than the smaller , inner planets in our system.
Carl Witthoft
<planetary-formation><terrestrial-planets>
Why does half of a planet's radius end up being the radius of the core?
usernumber
# Why does half of a planet's radius end up being the radius of the core?

(Asked by: username_0 on 2020-03-24)

[This answer](https://astronomy.stackexchange.com/a/22964/9527) makes the assumption that the ratio between the radius of a planet and the radius of its core is roughly constant shortly after planetary formation. Why should this be the case? Do we know why, when a planet forms, it ends up with half of its radius being core?

**Tags:** planetary-formation, terrestrial-planets

> **Comments:**
> **username_1**: Isn't this just based on assuming the same mix of heavy core-forming elements and lighter mantle/crust forming elements? Take any mass of the mix, turn it into a sphere and have a core form, and the ratio should be the same.  
> **username_2**: I don't think your linked question/answer makes that assumption for any other than the smaller , inner planets in our system.  

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