We could protect Earth from dangerous asteroids with a giant magnet

We could deflect potentially dangerous asteroids by using a giant magnet to gently pull them away. The idea avoids some of the pitfalls of the more traditional kinetic impactor method, which involves smashing something into an asteroid to move it, but it has yet to be tested, so we can’t be sure it would work.

The idea is called Non-Contact Orbital Velocity Adjustment, or NOVA Gunther Kletetschka at the University of Alaska Fairbanks introduced it at the Lunar and Planetary Science Conference in Texas on March 17.

In his calculations, he applied the NOVA concept to an asteroid called 2024 YR4, which briefly appeared to be on track to hit the Earth or the Moon in 2032, although further observations showed it would pass safely by. The asteroid is small, less than 70 meters in diameter, so it would make a relatively easy target for displacement.

The spacecraft itself would consist of a large magnet made of a coil of superconducting wire about 20 meters in diameter, powered by a nuclear fission reactor. Small boosters would steer its orbit around the asteroid, keeping it about 10 to 15 meters away from the rock, so the magnet could act on the iron in the asteroid.

If the asteroid were one big piece of iron, a magnet could simply pull it out of orbit, but most asteroids are not single huge rocks, but agglomerations of many smaller rocks held together by gravity, called debris piles.

“Because we have a rubble-pile-like structure with essentially zero tensile strength, we can’t effectively push on the whole body, because it’s like pushing on one ship among many ships on the ocean,” Kletetschka said in his presentation. A kinetic impactor would risk breaking the asteroid into pieces, so we’d have to deal with a lot of debris raining down on Earth.

Instead, the NOVA spacecraft would slowly pull rocks out of the debris pile in orbit and trap them in a magnetic trap at the center of its coil. Each fragment collected would increase both the mass and the magnetic field of the spacecraft, making it easier to extract the next fragment.

Basically, it would slowly shrink the asteroid and move it around while the spaceship turns into a second asteroid for us to control. Kletetschka calculated that it would take at least 170 days of continuous operation to fully deflect 2024 YR4.

“This electromagnetic deviation is likely, but we have critical uncertainties,” he said. First, we don’t know exactly how much iron there is in 2024 YR4, although an educated guess based on comparisons with other asteroids suggests that it would be enough. Second, maneuvering a spacecraft so close to an asteroid for such a long time has never been done before and would be difficult.

However, Kletetschka said that adding a tool to our planetary defense tool belt can’t be a bad thing, especially since it would have essentially zero risk of making the problem worse.

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