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Kinetic impact or nukes? How to save the Earth from an asteroid

The US space agency’s (NASA) DART mission to try to divert the trajectory of an asteroid with the impact of a spacecraft is at the moment the only way to defend the Earth from an approaching object with current technology.

With this demonstration, “methods that could be called upon in the future will be added to our toolbox,” Lindley Johnson of NASA’s planetary defense office said recently.

Other proposed ideas include a “gravity tractor” or a mission to blow up the object with a nuclear weapon.

kinetic impact

This technique is the one that NASA experimented with a few weeks ago. It consists of crashing a ship against an asteroid, in order to “push” it slightly, and thus divert its trajectory.

This first test will allow us to understand how the asteroid reacts and, therefore, better calculate the necessary force in the future.

The size of the ship used will depend on the size of the asteroid that threatens to collide with Earth.

If the threat of an asteroid impact on Earth were real, a mission would have to be launched a year or two in advance to deal with a small asteroid, or decades before the projected impact for objects hundreds of kilometers across.

A larger object could require the impact of multiple spacecraft.

gravity tractor

If an object’s approach is detected years or decades before it hits Earth, a spacecraft could be sent to fly alongside it long enough to deflect its trajectory with a gravitational pull on the part of the spacecraft, creating a ” gravity tractor.

“The virtue” of this method is its “totally good understanding” because “we know how gravity works,” DART program scientist Tom Statler said at a November briefing.

However, the mass of the spacecraft would be a limiting factor, and gravity tractors would be less effective for asteroids larger than 500 meters in diameter, which are precisely the ones that pose the greatest threat.

In a 2017 paper, NASA engineers proposed a way around this drawback: have the spacecraft pull material from the asteroid to enhance its own mass, and thus gravity.

But none of these concepts have been proven and it would take decades to build, test and launch.

Nuclear explotion

Another option is to drop nuclear bombs to redirect or destroy the asteroid.

“This may be the only effective strategy for the largest and most dangerous ‘planet-killing’ asteroids (over a kilometer in diameter),” a NASA article on the subject says, adding that the explosion could serve as the “last resource” in case the other methods fail.

But atomic weapons are controversial and banned for use in outer space.

Lori Glaze, director of NASA’s planetary science division, said in 2021 that the agency believed the best way to deploy the weapons would be some distance from the asteroid to impart force to the object without blowing it up into smaller pieces that could then be destroyed. multiply the threat to Earth.

A 2018 article published in the “Journal of Experimental and Theoretical Physics” by Russian scientists discussed the direct detonation scenario.

They built miniature models of asteroids and fired lasers at them. They showed that blowing up a 200-meter asteroid would require a bomb 200 times more powerful than the one that exploded over Hiroshima in 1945.

They also said it would be more effective to drill into the asteroid, bury the bomb, and then detonate it.

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