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Controversy over the origin of the nucleus of Mercury

For decades, it has been believed that collisions with other bodies during the formation of our solar system caused the loss of much of Mercury’s rock mantle (the layer between the core and the crust) and thus the dense metallic core passed to constitute a larger portion of the planet than before. However, now new research indicates that this was not the cause of Mercury having such a large iron-rich core.

The study was carried out by William McDonough, from the University of Maryland in the United States, and Takashi Yoshizaki, from the University of Tohoku in Japan.

McDonough and Yoshizaki developed a model that shows that the density, mass, and iron content of a rocky planet’s core are influenced by its distance from the magnetic field of its star.

McDonough previously developed a model for the composition of the Earth that planetary scientists often use to determine the composition of exoplanets (planets outside our solar system). His scholarly article on this work has been cited more than 8,000 times.

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

This colorful image of Mercury was produced using images captured by the MESSENGER space probe. These colors do not show what Mercury would look like when viewed up close to the human eye, but the false colors serve to enhance the chemical, mineralogical and physical differences between the rocks that make up the surface of that planet. (Image: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington)

The authors of the new study have found, in summary, that the density and proportion of iron in the core of a rocky planet correlate with the strength of the magnetic field around the star during planetary formation.

“The four inner planets of our solar system (Mercury, Venus, Earth and Mars) are made up of different proportions of metal and rock,” McDonough argues. “There is a gradient in which the metal content in the core decreases as the distance from each planet to the sun is greater.”

The new study suggests that magnetism should be taken into account in future attempts to describe the composition of rocky planets, including those outside our solar system.

The composition of a planet’s core is important to its potential to host life. On Earth, for example, its cast iron core creates a magnetosphere that protects the planet from cosmic rays, which are carcinogenic.

The study is titled “Terrestrial planet compositions controlled by accretion disk magnetic field”. And it has been published in the academic journal Progress in Earth and Planetary Science. (Source: NCYT from Amazings)

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