Magnetic fields are great for many things – directing explorers, levitating trains, and containing nuclear fusion reactions are just one example of what these invisible forces can do. Now we can ascribe another property to magnetic fields – they can give planets a rocky core.
This is the result of research by Dr. William McDonough of the University of Maryland and Dr. Takashi Yoshizaki from Tohoku University. The couple developed a model published in Progress in Earth and Planetary Sciences that shows how the sun’s magnetic field controlled the gradient of the raw materials from which the planets were formed.
We’re still studying the Sun’s magnetic field – and the Solar Orbiter spacecraft is an important part of the effort.
One of the results of their research was a correlation between the “density and the proportion of iron” of a newly formed planet and the strength of the star’s magnetic field during the formation of this planet. Although research cannot prove causality without experimental controls, it makes sense that iron, which is magnetic, is affected by the massive magnetic fields emitted by a young star.
Our own solar system is a reasonable example of this – Mercury, although the smallest planet, has an iron core that is ¾ of its mass. As the planets move away, their metallic cores make up less and less of their total weight, with Venus and Earth at about? of their weight in their cores while Mars clocks in at ¼.
UT video about the formation process of the planets.
However, the cores themselves are not generated by magnetic fields. The effect of magnetism is more subtle and pulls chunks of iron together into newly formed protoplanetary spheres. The gravitational forces then take over driving the dense iron into the core of the planet, where it is either melted or cooled, depending on a variety of other planetary formation factors. U
These planet formation factors apply not only in our own solar system, but also around the myriad stars that host extrasolar planets. Unfortunately, there is currently no way to detect the magnetic field of distant stars, so it would be impossible to include this data in an attempt to understand exoplanet formation in existing systems. But it is possible to infer what planets are made of from their emitted spectra and their estimated density.
Even Mars had a stronger magnetic field at one point, caused by its iron core, which itself could have been caused by the sun’s magnetic field. Photo credit: NASA / JPL / GSFC
Density estimates will play a key factor in future research on this topic. Dr. McDonough and his colleagues are looking for extrasolar planetary systems to confirm their theory. They are interested in whether the density of the planets decreases and they move further away from the sun. If so, it is a strong indication that magnetic forces could cause heavier elements (e.g. iron) to move towards the star.
The greatest impact of this work will initially be on the modeling and future models of planet formation. With a little luck, they can confirm their theory in other solar systems and consolidate the importance of magnetic fields in the formation of planets.
Learn more –
UMD – Why does Mercury have such a large iron core? Magnetism!
Advances in Earth and Planetary Science – Composition of terrestrial planets controlled by the magnetic field of the accretion disk
SciTechDaily – Are Scientists Wrong About Mercury? Its large iron core can be due to magnetism!
SlashGear – Mercury’s large iron core is due to the sun’s magnetic field
Mission statement –
Cutaway view of Mercury showing the size of its core.
Credit – NASA Goddard Space Flight Center