Here's why:

* Nickel-iron core: Mercury has a massive iron-nickel core that makes up a large percentage of its overall mass.

* Thick crust: Mercury has a relatively thin crust, estimated to be around 35-600 km thick. While your number is on the higher end of estimates, it's within the range considered possible.

Other planets also have iron cores, but their crusts are quite different:

* Earth: Earth has a much thicker crust and mantle than Mercury.

* Mars: Mars has a thinner crust than Earth, but it's still significantly thicker than Mercury's.

* Venus: Venus has a crust similar in thickness to Earth.

Let me know if you have any other questions about the planets!