Deep beneath our feet, thousands of kilometers deep, lies molten iron and nickel moving in the Earth's outer core. This movement creates our planet's magnetic field, a shield that protects life from the worst cosmic radiation for billions of years.
Understanding that the geomagnetic field is still a work in progress, new research from the European Space Agency ESA reveals an interesting fact about magnetic waves that exist on the surface of Earth's outer core, which borders the Earth's mantle.
Researchers report in the Proceedings of the National Academy of Sciences, magnetic waves are slowly sweeping the Earth's outer core at a speed of 1,500 kilometers per year. This happens once every seven years.
"Geophysicists have long theorized about the existence of such waves, but they are thought to occur on a much longer timescale than our study shows," said lead author Dr Nicolas Gillett of the Université Grenoble Alpes.
"Measurements of the magnetic field from instruments based on the Earth's surface suggest that there is some sort of wave action, but we need the global coverage that measurements from space offer to reveal what's really going on."
The space data comes from the Swarm mission as well as some old data from the German Champ and the first Danish mission. Swarm is made up of three identical satellites that can measure the magnetic field at Earth's core, as well as signals from other regions of the planet, from across space.
The data show that the waves are strongest at the equator and they align in a single column along the planet's axis of rotation. Just as the Coriolis force affects the motion of water in the planets north and south of the equator, these waves exhibit a magneto-Coriolis form of motion.
"Magnetic waves are likely to be triggered by disturbances deep within Earth's fluid core, possibly associated with buoyancy blobs. Each wave is defined by its typical period and length scale, and the period depends on the characteristics of the force at play. For magneto-Coriolis waves, the period indicates the intensity of the magnetic field in the Earth's core," explained Dr Gillett.
"Our research suggests that other such waves may exist, perhaps with a longer period, but this finding is subject to more research."
This research provides new insights into the behavior of the Earth's core and perhaps even more new knowledge will be revealed. Given the location of the waves, right at the bottom of the mantle, studying the behavior of the Earth's core may lead to new understanding of the lower mantle, including its electrical conductivity.