Our Strategies for Defending Against a Potential ‘City-Killer’ Asteroid Impact

While the chances are slim, an asteroid large enough to destroy an entire city could strike Earth in less than eight years. However, even if this space rock is on a collision course, experts assure us that humanity now has ways to defend itself.

NASA recently reported that the probability of asteroid 2024 YR4 impacting Earth on December 22, 2032, has risen to 3.1%—the highest forecasted risk for a large asteroid in modern history. But planetary defense experts remain confident.

“Don’t panic,” says Richard Moissl, head of the European Space Agency’s (ESA) planetary defense office. As astronomers gather more data, the odds of a direct impact are expected to increase slightly before ultimately dropping to zero. Even in the highly unlikely scenario that the probability reaches 100%, Moissl emphasizes, “we are not defenseless.”

The only planetary defense strategy successfully tested so far involves a direct collision. In 2022, NASA’s Double Asteroid Redirection Test (DART) mission deliberately smashed a spacecraft into the 160-meter-wide Dimorphos asteroid, altering its orbit. A similar approach could be used to nudge 2024 YR4 off course.

Non-Impact Deflection Methods

If there is enough time, subtler techniques could divert the asteroid without making direct contact:

• Gravity Tractor: A large spacecraft could fly alongside the asteroid, using its gravitational pull to gradually change the asteroid’s trajectory.
• Ion Beam: A spacecraft equipped with thrusters could direct a steady stream of charged particles at the asteroid, slowly pushing it off course.
• Reflective Coating: Scientists have even proposed spray-painting one side of the asteroid white. This would increase its reflectivity, altering how it absorbs and radiates heat, subtly shifting its path over time.

As a last resort, a nuclear explosion could deflect the asteroid. Unlike in Hollywood’s Armageddon, this would not involve drilling a bomb into the asteroid but rather detonating a nuclear device nearby. The resulting radiation and heat would vaporize part of the asteroid’s surface, generating enough force to change its trajectory.

While this method is considered for large, extinction-level asteroids, it poses risks. A nuclear explosion could shatter the asteroid, sending unpredictable fragments toward Earth. Additionally, the use of nuclear weapons in space comes with ethical, political, and legal challenges.

A less destructive alternative is using laser beams to vaporize part of the asteroid’s surface, creating thrust that nudges it away from Earth. Although lab experiments suggest this could work, experts do not consider it a top-tier strategy.

Preparing for Impact If Needed

If deflection efforts fail, scientists will still be able to predict the asteroid’s impact zone well in advance. Because 2024 YR4 is not a “planet killer,” its damage would be localized, at worst affecting a city. This means evacuation and impact mitigation could serve as the final line of defense.

“Seven and a half years is a long time to prepare,” Moissl reassures, emphasizing that the asteroid still has a 97% chance of missing Earth entirely.

Read Original Article: Science Alert

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