Why do Mercury have such a big Core (Magnetism)?
Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and its distance from the Sun as viewed from Earth never exceeds 28 degrees. Mercury rotatates in a way that is unique in the Solar System. It is tidally locked with the Sun in a 3:2 spin-orbit resonance, meaning that relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun.
https://www.sciencedaily.com/releases/2021/07/210702154314.htm