Earth's magnetic field plays a crucial role in protecting life from radiation generated by the solar wind and cosmic rays. This invisible shield draws most of its power from a juggernaut "geodynamo," which is the mechanism that converts the kinetic energy of our planet's convective liquid outer core into magnetism. But Earth's lithosphere, meaning its crust and upper mantle, contains magnetic minerals that contribute a small boost to this defensive field. The lithosphere is, in turn, sculpted by the shifting polarity of Earth's magnetic activity over time.
Scientists have been trying to better understand magnetic properties in the lithosphere for decades, but it can be challenging to detect the impact of the lithosphere's minor contribution to the field over the overwhelming flux produced by the core.
To help solve this and other mysteries relating to the Earth's magentic field, the European Space Agency (ESA) launched the Swarm satellite mission in November 2013. Consisting of three satellites—Alpha, Bravo, and Charlie—the constellation is capable of picking up extremely subtle magnetic signals and anomalies from Earth's rigid outer layer.
On Tuesday, Swarm mission leads unveiled the highest resolution map of the lithospheric magnetic field ever produced from space. Presented at the fourth annual Swarm Science Meeting, which runs from March 20-24 in Banff, Canada, the new research and animated map reveal the hidden magnetic features of the ground we walk on everyday.
Swarm map of lithospheric magnetic field. Video: ESA/DTU Space/DLR/YouTube
The simulated globe is based on Swarm data and past observations by the German Challenging Minisatellite Payload (CHAMP) project, which operated in orbit from 2000 to 2010. The animation begins with a topographical view of the planet, then overlays those geographical contours with color-coded areas indicating magnetic strength across the globe.
The blue end of the spectrum indicates weak signals, while red regions, known as crustal anomalies, are unusually rich in magnetic minerals. Some of these anomalies may have been caused by ancient meteorite impacts that enriched regions like Bangui, the capital of the Central African Republic, with extraterrestrial magnetic materials.
In addition to the color code, the map shows underlying ripples that correspond to the lithosphere's "magnetic stripes." This striping pattern is caused by the occasional reversal in the polarity of Earth's magnetic field, which occurs about four or five times every one million years (these flips are irregular and unpredictable).
When the field points north, magnetic minerals in the newly formed volcanic crust orient themselves along northern magnetic lines. When the field shifts to point south, young minerals are aligned in the opposite direction. In this way, the magnetic history of Earth is etched within iron, nickel, magnetite, and other magnetic materials embedded into the lithosphere.
"These magnetic stripes are evidence of pole reversals," said Dhananjay Ravat, a University of Kentucky geophysicist who contributed to the map, at the Swarm meeting. "Analyzing the magnetic imprints of the ocean floor allows the reconstruction of past core field changes. They also help to investigate tectonic plate motions."
"The new map defines magnetic field features down to about 250 kilometers and will help investigate geology and temperatures in Earth's lithosphere."
Subscribe to pluspluspodcast, Motherboard's new show about the people and machines that are building our future.