Why does Mercury have such a big iron core? Magnetism!

A brand-new research study contests the dominating hypothesis on why Mercury has a big core relative to its mantle (the layer in between a world’s core and crust). For years, researchers argued that hit-and-run crashes with other bodies throughout the development of our planetary system blew away much of Mercury’s rocky mantle and left the big, thick, metal core within. But brand-new research study exposes that crashes are not to blame—the sun’s magnetism is.

William McDonough, a teacher of geology at the University of Maryland, and Takashi Yoshizaki from Tohoku University established a design revealing that the density, mass and iron material of a rocky world’s core are affected by its range from the sun’s electromagnetic field. The paper explaining the design was released on July 2, 2021, in the journal Progress in Earth and Planetary Science.

“The four inner planets of our solar system—Mercury, Venus, Earth and Mars—are made up of different proportions of metal and rock,” McDonough stated. “There is a gradient in which the metal content in the core drops off as the planets get farther from the sun. Our paper explains how this happened by showing that the distribution of raw materials in the early forming solar system was controlled by the sun’s magnetic field.”

McDonough formerly established a design for Earth’s structure that is typically utilized by planetary researchers to identify the structure of exoplanets. (His critical paper on this work has actually been pointed out more than 8,000 times.)

McDonough’s brand-new design reveals that throughout the early development of our planetary system, when the young sun was surrounded by a swirling cloud of dust and gas, grains of iron were drawn towards the center by the sun’s electromagnetic field. When the worlds started to form from clumps of that dust and gas, worlds closer to the sun integrated more iron into their cores than those further away.

The scientists discovered that the density and percentage of iron in a rocky world’s core associates with the strength of the electromagnetic field around the sun throughout planetary development. Their brand-new research study recommends that magnetism ought to be factored into future efforts to explain the structure of rocky worlds, consisting of those outdoors our planetary system.

The structure of a world’s core is very important for its possible to support life. On Earth, for example, a molten iron core produces a magnetosphere that safeguards the world from cancer-causing cosmic rays. The core likewise consists of most of the world’s phosphorus, which is a crucial nutrient for sustaining carbon-based life.

Using existing designs of planetary development, McDonough identified the speed at which gas and dust was pulled into the center of our planetary system throughout its development. He factored in the electromagnetic field that would have been produced by the sun as it break into being and computed how that electromagnetic field would draw iron through the dust and gas cloud.

As the early planetary system started to cool, dust and gas that were not drawn into the sun started to clump together. The clumps closer to the sun would have been exposed to a more powerful electromagnetic field and hence would include more iron than those further away from the sun. As the clumps coalesced and cooled into spinning worlds, gravitational forces drew the iron into their core.

When McDonough integrated this design into computations of planetary development, it exposed a gradient in metal material and density that corresponds completely with what researchers understand about the worlds in our planetary system. Mercury has a metal core that comprises about three-quarters of its mass. The cores of Earth and Venus are just about one-third of their mass, and Mars, the outermost of the rocky worlds, has a little core that is just about one-quarter of its mass.

This brand-new understanding of the function magnetism plays in planetary development produces a kink in the research study of exoplanets, due to the fact that there is presently no approach to identify the magnetic residential or commercial properties of a star from Earth-based observations. Scientists presume the structure of an exoplanet based upon the spectrum of light radiated from its sun. Different components in a star emit radiation in various wavelengths, so determining those wavelengths exposes what the star, and probably the worlds around it, are made from.

“You can no longer just say, ‘Oh, the composition of a star looks like this, so the planets around it must look like this,'” McDonough stated. “Now you have to say, ‘Each planet could have more or less iron based on the magnetic properties of the star in the early growth of the solar system.'”

The next actions in this work will be for researchers to discover another planetary system like ours—one with rocky worlds topped large ranges from their main sun. If the density of the worlds drops as they radiate out from the sun the method it does in our planetary system, scientists might verify this brand-new theory and presume that a electromagnetic field affected planetary development.


The term paper, “Terrestrial planet compositions controlled by accretion disk magnetic field,” McDonough, W. F. and Yoshizaki, T., was released on July 2, 2021, in the journal Progress in Earth and Planetary Science.

Media Relations Contact: Kimbra Cutlip, 301-405-9463, [email protected]

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