On September 26, 2022, NASA successfully completed its Double Asteroid Redirection Test (DART) mission by intentionally crashing an unmanned spacecraft into the asteroid(小行星) Dimorphos. The goal was not to destroy the asteroid but to change its orbit. With the successful mission, NASA proved the concept that this technique could keep a potentially dangerous asteroid from crashing into Earth in the future.
Dimorphos is a small asteroid orbiting the larger asteroid Didymos. NASA noted that Dimorphos is not a threat to Earth, but because it passes relatively close to Earth, it was chosen as the target for the test mission.
Although the intended crash should change the asteroid's position slightly, it will add to a major shift over time. "If you were going to do this for planetary defense, you would do it 5, 10, 15, or 20 years in advance for this technique to work," said NASA program executive Andrea Riley. "This is why we test. We want to do it now rather than when there's an actual need."
Asteroids can pose a significant threat to planet Earth. For example, around 66 million years ago, an asteroid around 6 to 9 miles across struck the Earth in what is now the Yucatan Peninsula. The resulting impact was so catastrophic(灾难性的) that it caused one of the largest extinction events in Earth's history. Therefore, DART's success is an important step forward in protecting the planet from potential damage from an asteroid. This shows humans are no longer powerless to prevent this type of natural disaster.
The DART spacecraft was launched by NASA on November 24, 2021. It was accompanied by another craft called LICIACube, supplied by the Italian Space Agency, and separated from DART just 15 days before the crash. LICIACube remained in orbit around the asteroid and took photographs of the crash and material ejected(弹出) from the asteroid's surface.
