We could protect Earth from dangerous asteroids using a giant magnet

We can gently separate potentially dangerous asteroids using a giant magnet. This idea avoids some of the disadvantages of the more traditional kinetic impactor method, which involves smashing something into the asteroid to move it, but it hasn’t been tested yet, so we can’t be sure it will work.

This idea is called non-contact orbital velocity adjustment, or NOVA. Gunther Klettska at the University of Alaska Fairbanks presented it March 17 at the Lunar and Planetary Science Conference in Texas.

In their calculations, they applied the NOVA concept to an asteroid called 2024 YR4, which briefly looked like it might be on a trajectory to collide with Earth or the Moon in 2032, although further observations showed it would pass safely by. The asteroid is small, less than 70 meters wide, so it would present a relatively simple target to move.

The spacecraft will include a large magnet made of a coil of superconducting wire approximately 20 meters in diameter, which will be powered by a nuclear fission reactor. Small boosters will control its orbit around the asteroid, keeping it about 10 to 15 meters away from the rock, so that magnets can act on the iron within the asteroid.

If the asteroid were a large piece of iron, a magnet could easily pull it off track, but most asteroids are not single giant rocks, but rather clusters of many smaller rocks barely held together by gravity alone, called debris piles.

“Because we have this debris pile-like structure with essentially zero tensile strength, we can’t efficiently push on the entire body because it’s like pushing a boat among many boats in the ocean,” Klettska said in her talk. A kinetic impactor would risk breaking up the asteroid, leaving us with lots of fragments raining down on Earth.

Instead, an orbiting Nova spacecraft will slowly pull rocks from the debris pile and capture them in a magnetic trap at the center of its coil. Each piece collected will increase both the spacecraft’s mass and magnetic field, making it easier to extract the next piece.

Essentially, this will slowly shrink the asteroid and move it, while turning the spacecraft into another asteroid that, crucially, we can control. To completely deflect 2024 YR4, Klettska calculated that it would require at least 170 days of continuous operations.

“This electromagnetic deflection is plausible, but we have serious uncertainties,” he said. For one, we don’t know exactly how much iron is in 2024 YR4, although an educated guess based on comparisons with other asteroids suggests it would be substantial. For another, operating a spacecraft so close to an asteroid for so long has never been done before and will be difficult.

However, Klettska said, adding a tool to our planetary defense toolbelt might not be a bad thing, especially because it would have essentially zero risk of worsening the problem.