Our planet's trusty magnetic field—an invisible barrier created by the churning of molten-hot matter in Earth's core—protects us from the lethal space radiation that engulfs most of the known universe. Without this field, Earth today would look as barren as Mars. Scientists have a hard time imagining how life anywhere could exist without one.

According to a new study out today, magnetic fields like Earth's may have been far more common in our early universe than scientists ever suspected. As a team of planetary scientists led by James Bryson of the University of Cambridge reports in the journal Nature, space rubble such as asteroids and meteoroids once created their own powerful magnetic fields that lasted for millions to tens of millions of years. This new discovery not only radically alters our understanding of asteroid evolution, but also bolsters the possibility that life—or the delicate chemical precursors to life—could survive by hitchhiking on space rubble.

"The fact that you can get this very efficient, very long-lived magnetic activity on asteroids is really going to change the perspective on how we think these things evolved," Bryson says. "And from an even wider perspective, I think it's also becoming incredibly apparent that asteroids in many ways are just small, sped-up versions of our own planet."

Molten Matter

Bryson and his team made this discovery after painstakingly studying the magnetic cores of meteorites that crashed into Earth. They used x-ray and magnetic imaging to map the magnetic fingerprints. After collecting these fingerprints, the scientists plugged them into a computer model that not only extrapolated what the former meteoroid's magnetic field had looked like, but also how that had changed over its lifespan.

Scientists had long believed that asteroids and meteoroids could have emanated only brief magnetic fields that lasted just a few thousand years after their creation—when the asteroid's molten core is still sloshing around. But Bryson found that the space rocks had magnetic fields that lasted much, much longer. These longer-lasting magnetic fields had to have been created by an entirely different force, the team decided.

Bryson thinks it works like this: "When the temperature of the core lowers enough, it starts to solidify. Most of the stuff that makes up this core is metal (mostly iron and nickel,) but there are also a couple of really light elements mixed in. As the metal slowly solidifies around these light elements, the light elements transform into liquid, and push outwards from the core. And it's the convection that results from that liquid moving upward that creates the magnetic field."

Life Hitches a Ride

This new understanding of asteroids has tantalizing implications for the panspermia hypothesis—the idea that life, or its precursor chemicals, could have found its way to Earth from elsewhere in the universe by hitchhiking on asteroids, meteors, or comets. Bryson is careful to point out that this is still a very open question, and his new finding is not concrete evidence that meteors and asteroids did or could support life. However, he says, it certainly strengthens the case.

"Obviously Earth's magnetic field has been linked to life on the Earth. And if magnetic fields are crucial for life, the increased magnetic activity in the solar system helps come up with a cohesive or coherent story of life in the solar system."

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