An unmanned spacecraft built for NASA’s Double Asteroid Redirection Test (DART) successfully slammed into the Dimorphos asteroid Monday evening, aiming to test a technique that scientists hope could stop dangerous asteroids from threatening Earth.
Dimorphos never posed any risk to our planet, but Johns Hopkins says it was “the ideal candidate for humankind’s first planetary defence experiment”. It orbits around a larger Sun-orbiting asteroid called Didymos, and its trajectory is easy to observe from Earth, allowing scientists to measure how the DART crash changes Dimorphos’ orbit.
If US$330 million seems like a lot to burn on a spacecraft that’s designed to crash into a space rock, NASA and Johns Hopkins say the mission is designed to help prevent potentially catastrophic asteroids from careening toward Earth. DART tested a technique known as “kinetic impact deflection,” in which the course of an asteroid is altered through a fast collision with a human-produced object, redirecting it away from the planet. NASA is currently tracking some 1,419 near-earth asteroids that have a nonzero chance of hitting Earth, though in some cases, these asteroids are decades or even a century away from the planet. The agency says no known asteroids that are larger than 140 metres—which is large enough to cause mass casualties—poses a significant threat to the planet over the next century, though even a smaller asteroid could cause injuries and destruction.
Johns Hopkins says kinetic impact deflection is the most well-developed known method for diverting asteroids from Earth, but scientists have offered up a few other strategies that could save us from going the way of the dinosaurs. In particular, a spacecraft could fly alongside an asteroid and use its gravity to gently nudge the rock onto a different trajectory. Using a nuclear weapon to destroy an asteroid may have worked for Bruce Willis, but some experts fear explosives could break an asteroid into fragments that are still large enough to hit Earth, and NASA says asteroids move far too quickly to destroy minutes or hours before crashing into the planet.