DART, NASA's test to stop an asteroid from hitting Earth

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Highlights

DART is the first planetary defense mission to test a method of deflecting an asteroid on course to hit Earth.

The threat from asteroid impacts is small, but real—and preventable. Missions like DART are essential to help us understand how to stop dangerous asteroids.

The Planetary Society works to improve asteroid detection and reconnaissance, mature deflection technologies, and develop global response strategies.

What is DART?

What should we do if we find a dangerous asteroid on course to hit Earth? There are a number of possible deflection techniques, ranging from extreme (a nuclear blast) to benign (a heavy spacecraft uses gravity to nudge the asteroid off-course).

Somewhere in between is the kinetic impactor technique. The concept is simple: Slam one or more spacecraft into the asteroid at high speed to change its orbit and move Earth out of the crosshairs. This technique works particularly well if used far in advance, since small nudges can add up to big changes later on.

DART, NASA's Double Asteroid Redirection Test, is the first space mission to test this or any other asteroid deflection technique. DART launches between November 2021 and February 2022 and will arrive at near-Earth asteroid Didymos in September 2022. The spacecraft won't slow down, intentionally crashing into the asteroid's small moon Dimorphos. The crash should change the time it takes Dimorphos to orbit Didymos, proving the kinetic impactor technique works.

Didymos and Dimorphos are particularly well-suited targets for DART. Although they are relatively small—Didymos measures just 780 meters (a half-mile) across and Dimorphos measures only 160 meters (525 feet) across—they pass in front of each other as seen from Earth. Optical ground-based telescopes see them as a single point of light that fluctuates in brightness as Dimorphos circles Didymos; the interval of those fluctuations will change after DART's impact. Additionally, Didymos and Dimorphos do not come close enough to Earth for DART to inadvertently send them hurtling towards our planet.

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