NASA's Double Asteroid Redirection Test (DART) mission was designed to test a method of deflecting an asteroid for planetary defense, using the "kinetic impactor" technique. DART slammed into a small asteroid — Dimorphos — in a bid to change the moonlet's orbital speed by a fraction of a percent, according to NASA. Though Dimorphos poses no threat to Earth, the ambitious mission mimics what NASA scientists would do if an asteroid were headed toward Earth.
Though the threat from asteroid impacts is small, it is a threat nonetheless and is something to be prepared for. We only need to look at past impact events such as the massive “Chicxculub” asteroid impact that is credited with the extinction of the dinosaurs 65 million years ago, to see the catastrophic effects an impact can have on life on Earth. “The risk of a catastrophic impact on Earth is remote but real.” NASA scientists have said. NASA has found about 40% of the large asteroids as wide as 500 feet (140 meters) that could pose a threat to the Earth and regularly scan the sky for more. Potentially launching by 2026, NASA is also developing a new space telescope sentinel called the Near-Earth Object Surveyor specifically designed to seek out hazardous asteroids in the solar system.
Early detection of near-Earth asteroids is the first step in planetary defense. Approximately 30 new discoveries of near-Earth catastrophes are made each week and at the start of 2019, there were more than 19,000 discovered near-Earth asteroids according to NASA.
DART's target was the binary asteroid system Didymos, which means "twin" in Greek. The system consists of a near-Earth asteroid Didymos measuring 0.48 miles (780 meters) across and its moonlet Dimorphos measuring 525 feet (160 meters) across. DART deliberately impacted the moonlet Dimorphos at speeds of 4.1 miles per second (6.6 km/s). That's an eye-popping 14,760 mph (23,760 kph).
An impact at this speed should cause the moonlet's orbital speed to change by a fraction of a percent and this shift should be enough to change its orbital period by several minutes. According to NASA, the change in Dimorphos' orbit around Didymos will be observed and measured by telescopes on Earth, to see whether the mission has succeeded.
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References:
Dobrijevic, Daisy. “NASA’s DART Asteroid-smashing Mission: The Ultimate Guide.” Space.com, 27 Sept. 2022, www.space.com/dart-asteroid-mission.