Researchers from the University of Maryland and Tohoku University have identified that Mercury has a large and solid-iron inner core than its mantle, measuring some 2,000 kilometres almost as large as that of Earth.
The study reveals that Sun’s magnetism is the reason for changes in the layer between Mercury’s core and its crust. The researchers made this observation using radio observations from MESSENGER (a NASA robotic space probe that orbited the planet Mercury between 2011 and 2015, studying its chemical composition, geology, and magnetic field) to determine the precise position of the planet’s rotational pole. Incorporating the ground-based radar data, collected in 2007, they observed small shifts in the planet’s 58-day spin, known as ‘librations’ that indicated the presence of at least a partially molten metal core.
However, this study disputes the prevailing hypothesis on why Mercury has a big-sized core relative to its mantle. Earlier, scientists were of the view that hit-and-run collisions with other celestial bodies during the formation of our solar system resulted in much of Mercury’s rocky mantle being removed. Thus, what left behind was the big and dense metal core inside.
Findings of the Study
Some key findings of the study are as follows:
- Developing a model, the researchers have shown that the density, mass, and iron content of a rocky planet’s core are influenced by its distance from the Sun’s magnetic field.
- There is a slope in which the metal content in the core drops off as the four inner planets of our solar system get further from the Sun. The distribution of raw materials in the early forming solar system was controlled by Sun’s magnetic field.
- 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 towards the centre by the Sun’s magnetic field. When the planets began to form from clumps of that dust and gas, planets closer to the Sun incorporated more iron into their cores than those which were far away.
- Mercury’s metallic core fills nearly 85 per cent of the planet’s volume, which is huge as compared to the cores of the solar system’s other terrestrial planets.
- Mercury’s interior is still active due to the molten core that powers the planet’s weak magnetic field, relative to Earth’s.
- Mercury’s interior cooled more rapidly than the Earth’s.
- Mercury may help us predict how Earth’s magnetic field will change as the core cools.
- Among the terrestrial planets, Mercury is an exception because its core accounts for three-fourths of its total mass. Its density, given the generally higher iron content, exceeds all other planets.
- Mercury has a large and solid inner core. As per an estimate, the iron core of Mercury is about 2,000 km wide and makes up about half of it’s entire core about 4,000 km. In contrast, Earth’s solid core is about 2,400 km across, taking up a little more than a third of this planet’s entire core.
Magnetic Field of the Young Sun
The developed model by researchers, at the University of Maryland and Tohoku University, represents the chemical composition of the planets as a function of heliocentric position. Based on the model, they postulated that the planet’s density, mass, and iron content vary with the distance between it and the solar magnetic field. The Sun is made of plasma, which is highly conductive, capable of supporting and amplifying the magnetic field. However, macroscopic motions like convection or rotation amplify them further. As a result, young stars, rotating very quickly on themselves, have strong magnetic fields, which attract the iron particles towards the centre of the solar system, producing a gradient visible on both planets and meteorites. Thereafter, the accumulated iron sinks into the core, under the influence of gravity, and pushes out the lighter oxygen.
However, the addition of a celestial collision cannot be ruled out as Mercury still contains a lot of iron!
The study was published in the American Geophysical Union journal Geophysical Research Letters.
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