An illustration of the DART spacecraft heading toward the Didymos binary asteroid system (Credit: NASA/Johns Hopkins Applied Physics Lab, Public domain/ Wikimedia Commons)

On September 26, 2022, NASA's golf cart-sized DART (Double Asteroid Redirection Test) spacecraft intentionally crashed into a distant asteroid. The spectacular collision, observed by telescopes worldwide, was NASA's first practical attempt to alter the path of an asteroid. The $325 million mission was part of the space agency's overall planetary defense strategy to protect Earth from the impact of an errant space rock.

"We're embarking on a new era of humankind, an era in which we potentially have the capability to protect ourselves from something like a dangerous hazardous asteroid impact. What an amazing thing. We've never had that capability before," said Lori Glaze, Director of NASA's Planetary Science Division.

DART's target was a small asteroid called Dimorphos. The space rock measures 530 feet (160 meters) in diameter, or about the size of the Great Pyramid of Giza. It is currently about seven million miles away from Earth. Dimorphos orbits a larger, 2,560-foot (780-meter) asteroid called Didymos.

Asteroid Didymos (top left) and its moonlet, Dimorphos, about 2.5 minutes before the impact of NASA's DART spacecraft (Credit: NASA/Johns Hopkins APL)

Neither asteroid is a threat to Earth. The binary asteroid system was selected because observing a change in the orbits of two space rocks is much easier than that of a single asteroid. Additionally, Didymos has the physical properties of objects classified by NASA as Potentially Hazardous Asteroids (PHA).

NASA's team will now use ground-based telescopes to determine if DART's impact altered Dimorphos's orbit around Didymos. The researchers expect the collision to shorten Dimorphos's orbit time by roughly ten minutes.

In October 2024, the European Space Agency (ESA) will launch the Hera Mission to conduct detailed surveys of the two asteroids. The researchers are particularly interested in knowing more about the crater caused by DART's collision. They also want to obtain precise measurements of Dimorphos's mass. If successful, Hera will be the first spacecraft to explore a binary asteroid system. It will also be the first to visit a space rock as small as Dimorphos.

Resources: NASA.gov, The Verge.com