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  • Saloni Khanduri

Why Does Mercury Have Such a Big Iron Core?

The core of a planet is its innermost layer. A planetary core can be solid, liquid or a mix of both like Earth’s core. Mercury has the largest core relative to its size with 85% of its radius being its core. This has been a topic of discussion for decades now. Many said that collisions with other bodies during the formation of our solar system caused its rocky mantle to get chipped away and left the big, dense, metal core inside. However, new research reveals that collisions are not to blame, the sun’s magnetism is.

Researchers have found that the density and proportion of iron in a rocky planet’s core correlate with the strength of the magnetic field around the sun during planetary formation. This suggests that magnetism should be factored into future attempts to study the composition of rocky planets, even to those outside our solar system. The composition of a planet’s core is important for its potential to support life. Earth has a molten iron core which forms 15 percent of its volume and creates a magnetosphere that protects the planet from cancer-causing cosmic rays. The core also contains the majority of Earth’s phosphorus which is an important nutrient for sustaining carbon-based life. There is currently no method to determine the magnetic properties of a star from Earth-based observations. Therefore, this new study has caused a slight kink in the study of exoplanets. Scientists infer the composition of an exoplanet based on the spectrum of light radiated from its sun. Different elements in a star emit radiation in different wavelengths, so measuring those wavelengths reveals what the star, and presumably the planets around it, are made of.

The next steps in this work will be for scientists to find another planetary system like ours – one with rocky planets spread over wide distances from their central sun. The theory will be proved if the density of the planets drops as they radiate out from the sun the way it does in our solar system and scientists can infer that a magnetic field influences planetary formation.

View of Mercury from space

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