Why is Mercury having a big iron core?


The strength of the magnetic field weakened as it got further away from the Sun. Mercury formed in the prime location - close to where the Sun's magnetic field was strongest, thus explaining its large iron core.

Scientists have pinpointed the strong magnetic field of the early sun as the reason behind the radial variation of rock and metal in rocky planets' cores. This magnetic field, which pulled small iron grains inward, explains Mercury's big iron core and why Mars has so little iron in its core.

The details of their research were published in the journal Progress in Earth and Planetary Science on July 5, 2021.

Planets have iron cores surrounded by a rocky shell, mostly made up of mantle and a thin skin of crust. The four inner planets of our Solar System, Mercury, Venus, Earth, and Mars have their own distinctive size and density. These differences have long since puzzled scientists.

Mercury has a metallic core making up about 3/4 of its mass, with the remaining 1/4 being a rocky silicate shell. The cores of Earth and Venus possess a metallic core of only 1/3 of their mass, with the rest being rock. Mars has a measly core comprising only 1/4 of its mass.

These radical changes in metal content offer clues about what controlled the distribution of raw materials in the early formation of the solar system.

During this period, swirling gas and dust cloud drew matter into the Solar System's center, thus forming the Sun. The rapid delivery to the center caused many collisions and heated the inner region of the Solar System. When the Sun was big enough to have its own internal gravity, it caused its proton-rich core to ignite its nuclear fuel, brightly turning on the Sun. Following this, the Sun's core began convecting, creating a dynamo generating a strong magnetic field.

The high temperatures of the inner Solar System turned elements into a vapor state. As the element cloud cooled down it rained out mineral compounds. Evidence from primitive meteorites reveals the compounds precipitated were either silicates or metals. The sun's magnetic field pulled the metal particles inwards.

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