Mercury's Bizarre Magnetic Field Reveals a Different Interior from Earth's

Mercury and Earth may both be rocky planets with iron cores, but their magnetic fields are drastically differently. Now, researchers have found that Mercury's interior may differ in a way that explains why it has such a bizarre magnetic field.

Planets in our solar system have different magnetic fields that help shield them from the sun's energy-charged particles. These fields can differ widely in strength; for example, while Earth's is powerful, Jupiter's is more than 12 times stronger. Mercury's magnetic field, in contrast, is overall rather weak, but is about three times stronger at its northern hemisphere than at its southern one.

This peculiar magnetic field reveals that Mercury's center may be different from Earth's. Within Earth's core, iron turns form a liquid to a solid at the inner boundary; this results in a solid inner part and a liquid outer part. In Mercury, in contrast, the iron probably turns from a liquid to a slide at the core's outer boundary.

In order to better understand Mercury's interior, the researchers conducted mathematical modeling of the processes that generate Mercury's magnetic field. They included factors such as how fast Mercury rotates, its chemistry and the motion of fluid inside the planet.

"It's like a snow storm in which the snow formed at the top of the cloud and middle of the cloud and bottom of the cloud too," said Christopher Russell, one of the researchers, in a news release. "Our study of Mercury's magnetic field indicates iron is snowing throughout this fluid that is powering Mercury's magnetic field."

The findings reveal that planets may have multiple ways of generating a magnetic field. In addition, it shows how Mercury's field differs so much from Earth's, despite the fact that the two are both rocky planets.

"Planets are different from one another," said Hao Cao, one of the researchers, "They all have their individual character."

The findings are published in the journal Geophysical Research Letters.