Magnetism, not cataclysm, may be the cause of Mercury’s giant iron core

Mercury’s disproportionately massive core could be the result of the Sun’s powerful magnetic influence rather than the consequence of a cataclysmic collision with another body in the ancient past, according to the results of a new study.

Since the advent of spaceflight, humanity has sent only three spaceships to unravel the secrets held by Mercury, the innermost planet in our solar system. In the 1970s, NASA’s Mariner 10 spacecraft made three separate overflights of the planet, capturing high-resolution images and capturing data about Mercury’s magnetic field.

Decades later, on March 17, 2011, the agency’s MESSENGER spacecraft became the first probe to orbit Mercury. He then spent four years characterizing the alien world in unprecedented detail. Meanwhile, the joint European / Japanese mission BepiColombo is still on its way to the planet and is expected to arrive at the end of 2025.

As a result of these efforts, astronomers have learned a lot about Mercury, but it still holds a plethora of mysteries that the scientific community has yet to solve.

One of these mysteries is related to the internal structure of the planet. Analysis of data collected by orbiting spacecraft taking detailed readings of Mercury’s gravitational signature had in the past revealed that the planet had an iron core of disproportionate mass to the size of its mantle.

To be more precise, it is estimated that the core is about three-quarters of the mass of Mercury and has a radius of about 1,289 miles (2,074 km), while the outer rocky shell of the planet is only 250 miles (400 km). in depth. This makes it the second densest planet in the solar system.

Until now, the main theory as to why Mercury has such an unusually large nucleus for such a small planet has centered on the idea that it was in fact a much larger planet that had fallen victim to a planetary collision in the distant past. According to this theory, the cataclysmic force of the interaction was sufficient to remove much of Mercury’s outer shell, leaving behind a shallow mantle to cover the core of the once larger planet.

However, according to the new study, Mercury’s unusual structure may actually be the result of the natural influence of the Sun’s magnetic field.

The authors created a new computer model of the primordial cloud of dust and gas from which planets in the solar system would eventually form, and simulated the effect of a young Sun’s magnetic field on the swirling mass. It was discovered that the magnetic influence of our mother star brought the iron grains embedded in the cloud closer together. This resulted in the planets that formed closest to the Sun to have a much larger iron core than those that would one day orbit in the most distant regions of the solar system.

The researchers combined their model with previous research on planetary formation, in order to calculate the speed at which the material would be attracted to the Sun. They found that the planetary compositions predicted by their model correlated well with the actual planets that make up our solar system today.

As well as shedding light on how our home solar system came to merge and subsequently mature, the new research could also have important implications for astronomers hoping to better understand distant exoplanets spread across the galaxy.

“You can’t just say, ‘Oh, a star’s makeup looks like this anymore, so the planets around it have to look like this,” said William McDonough, professor of geology at the University of Maryland and one of the authors. of the new study. “Now you have to say, ‘Each planet might have more or less iron depending on the star’s magnetic properties when the solar system starts growing.'”

The team is now looking for an alien star system in which rocky planets are known to orbit, with which they can further test their theory.

The article was published in the journal Advances in Earth and Planetary Sciences.

Source: University of Maryland


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