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Nuclear bombs. That’s the go to answer for incoming space objects like asteroids (小行星)and comets as far as Hollywood is concerned. Movies like Deep Impact and Armageddon rely on nuclear weapons, delivered by stars like Bruce Willis, to save the world and deliver the drama.

But planetary defense experts say in reality, if astronomers spotted a dangerous in- coming space rock, the safest and best answer might be something more subtle, like simply pushing it off course by crashing it with a small spacecraft.

That’s just what NASA did on Monday evening, when a spacecraft headed straight in- to an asteroid called Dimorphos, which is around 7 million miles away and poses no threat to Earth. It’s about 525 feet across and orbits another larger asteroid.

In images streamed (传输)as the crash neared, the egg-shaped asteroid grew in size from a little spot on screen to have its full rocky surface come quickly into focus before the signal went dead as the craft hit right on target.

Events happened exactly as engineers had planned, they said, with nothing going wrong. “As far as we can tell, our first planetary defense test was a success, ” said Elena Adams, the mission systems engineer, who added that scientists looked on with “both terror and joy” as the spacecraft neared its final destination.

The crash was the peak of NASA’s Double Asteroid Redirection Test ( DART ), a 7-year and more than $300 million effort which launched a space vehicle in November of 2021 to per- form humanity’s first ever test of planetary defense technology. It will be about two months, scientists said, before they will be able to determine if the crash was enough to drive the asteroid slightly off course, probably shortening its original orbit.

NASA plans to launch an asteroid-hunting space telescope named NEO Surveyor in 2026. “We’ve tracked lots of space rocks, especially the larger ones that could cause ex- tinction-level events. Thankfully, none currently threaten Earth. But many asteroids the size of Dimorphos haven’t yet been discovered, and those could potentially take out a city if they came crashing down. ” explains Lindley Johnson, NASA’s Planetary Defense Officer.