Ancient meteorites reveal that young asteroids may have generated powerful magnetic fields for hundreds of millions of years longer than previously thought. The discovery could explain the long-lasting magnetism elsewhere in the early solar system, such as on the young moon (SN online: 12/04/14).
University of Cambridge planetologist James Bryson and his colleagues examined two South American meteorites left behind by asteroids about 400 kilometers wide (about a ninth of the moon’s diameter). Tiny pockets of iron and nickel encrusted in space rocks aligned with the magnetic field of their parent asteroid when they formed billions of years ago, providing a datable snapshot of asteroid magnetism. By inspecting iron and nickel using X-rays, the team found that each asteroid produced a strong magnetic field for over 100 million years.
This is much longer than can be explained by the heat mixing the molten interior of an asteroid and generating a magnetic field, which would last at most 10 to 50 million years until the rock collapsed. cools.
Researchers to propose in January 22 Nature that as the core of an asteroid solidifies, lighter elements such as sulfur push outward and form swirling patterns. The vortex maintains the magnetic field for up to 350 million years after the asteroid cools too much for thermal convection, the researchers say.
Editor’s Note: This article was updated on January 22, 2015 to correct the metals used to study the asteroid’s magnetic field history. It was iron and nickel, not lead.