Questions Corner | Why does Mercury have such a large iron core?

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A study by researchers at the University of Maryland challenges the dominant hypothesis as to why Mercury has a large nucleus in relation to its mantle (the layer between its core and its crust). Scientists had argued that collisions with other bodies during the formation of our solar system caused much of Mercury’s rocky mantle to shrink, leaving behind the large dense metal core inside. But new research shows that the Sun’s magnetism is the cause, not the collisions.

Researchers have developed a model showing that the density, mass and iron content of a rocky planet’s core are influenced by its distance from the Sun’s magnetic field. (Advances in Earth and Planetary Sciences).

There is a gradient in which the metal content of the core decreases as the four inner planets of our solar system move away from the Sun. Current work explains this by showing that the distribution of raw materials in the early-forming solar system was controlled by the Sun’s magnetic field.

The new model shows that at the start of our solar system’s formation, when the young Sun was surrounded by a swirling cloud of dust and gas, grains of iron were drawn to the center by the Sun’s magnetic field. When planets began to form from clusters of this dust and gas, planets closer to the sun incorporated more iron into their cores than those farther away.


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