We could protect Earth from dangerous asteroids using a huge magnet

We could redirect potentially dangerous asteroids using a massive magnet to gradually dismantle them. This approach avoids some challenges faced by the traditional kinetic impactor method, which involves colliding an object with an asteroid to alter its path. However, this new method remains untested, so its effectiveness is uncertain.

The concept, known as non-contact orbital velocity adjustment (NOVA), was presented by Gunther Kletetschka from the University of Alaska Fairbanks at the Lunar and Planetary Science Conference in Texas on 17 March. He applied the NOVA idea to the asteroid 2024 YR4, which once appeared to be on a collision course with Earth or the moon in 2032. Further observations confirmed it would pass safely. The asteroid is less than 70 meters in diameter, making it a relatively easy target to alter.

The spacecraft would feature a large magnet made from a 20-meter coil of superconducting wire, powered by a nuclear fission reactor. Small boosters would maintain its orbit around the asteroid, positioning it 10 to 15 meters from the rock, so the magnet could influence the asteroid’s iron content.

If the asteroid were a single iron chunk, the magnet could simply redirect it. However, most asteroids are not solid rocks but clusters of smaller rocks, known as rubble piles, loosely held together by gravity.

“Because we have this rubble pile-like structure with essentially zero tensile strength, we cannot efficiently push on the whole body because it’s like pushing on one boat among many boats on the ocean,” said Kletetschka in his talk. A kinetic impactor risks shattering the asteroid, resulting in multiple fragments falling to Earth.

Instead, a NOVA spacecraft in orbit would gradually pull rocks from the rubble pile and trap them magnetically at the coil’s center. Each piece collected would increase the spacecraft’s mass and magnetic field, facilitating the extraction of subsequent fragments.

This process would gradually reduce the asteroid’s size and move it while transforming the spacecraft into a controllable second asteroid. Kletetschka estimated that fully deflecting 2024 YR4 would require at least 170 days of continuous operation.

“This electromagnetic deflection is plausible, but we have critical uncertainties,” he said. One concern is the unknown iron content in 2024 YR4, although comparisons with other asteroids suggest it might suffice. Additionally, maneuvering a spacecraft so close to an asteroid for extended periods is untested and would be challenging.

Nevertheless, Kletetschka emphasized that adding this method to our planetary defense arsenal would pose virtually no risk of exacerbating the problem.