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NASA’s Asteroid-Smashing DART Mission Deemed a Success


The first mission to test a technology that one day might protect Earth from a catastrophic asteroid impact achieved its goal on Sept. 26, when a fast-moving spacecraft smashed into and changed the trajectory of a distant space rock, the National Aeronautics and Space Administration said Tuesday.

NASA said the intentional collision between its uncrewed spacecraft and the 525-foot-wide asteroid, called Dimorphos, successfully shifted the asteroid’s orbit around a larger asteroid called Didymos.

“This is a watershed moment for planetary defense and a watershed moment for humanity,” NASA Administrator Bill Nelson said Tuesday at a press briefing, adding that the mission “shows NASA is trying to be ready for whatever the universe throws at us.”

The spacecraft was moving more than 14,000 miles an hour when it struck Dimorphos, which was about 7 million miles from Earth at the time of impact and doesn’t pose a threat to our planet.

“The impact was perfectly executed,” said Megan Bruck Syal, the planetary defense project lead at Lawrence Livermore National Laboratory in California and a co-investigator of the $325 million mission, known as the Double Asteroid Redirection Test, or DART. She called the mission a great success.

Double Asteroid Redirection Test

On Sept. 26, NASA intentionally smashed its DART spacecraft into Dimorphos, a small asteroid orbiting a larger one called Didymos.

Since the collision, DART team members have been working to quantify the shift in Dimorphos’ orbit. Before impact, it took Dimorphos 11 hours and 55 minutes to complete one orbit around Didymos. Now that time has been shortened to 11 hours and 23 minutes, Mr. Nelson said.

The magnitude of the change to Dimorphos’s orbit came as a pleasant surprise, said Harrison Agrusa, a University of Maryland astrophysicist and DART investigation team member. “We were envisioning maybe more of a 10-, 20-minute change,” Dr. Agrusa said.

The team members based their calculations on post-impact observations of the asteroid pair by the James Webb and Hubble space telescopes and ground-based observatories on every continent.

“The way people have converged to an answer so rapidly is really impressive,” Dr. Bruck Syal said.

While a 32-minute change might seem insignificant, it may be all that is needed to deflect the path of a dangerous asteroid—as long as the deflection happens far enough in advance of a potential strike on Earth.

An image of Dimorphos taken by a camera aboard NASA’s DART spacecraft before impact.



“That small amount adds up to a bigger change over time,” Dr. Nancy Chabot, DART coordination lead and a planetary scientist at Johns Hopkins University Applied Physics Laboratory in Laurel, Md., said before the collision. The research center built and operated the DART spacecraft and manages the mission for NASA’s Planetary Defense Coordination Office.

There are no asteroids larger than 140 meters in diameter known to be on a collision course with Earth within the next 100 years, according to NASA. But the agency has been able to find and track only an estimated 40% of all asteroids and comets that size whose orbits bring them close to Earth.

If an asteroid the size of Dimorphos were to strike a populated area, it could bring about a disaster “on the scale we’ve never seen before,” said NASA’s Planetary Defense Officer Lindley Johnson.

There have been devastating asteroid strikes in Earth’s history, including the impact from a 6-mile-wide space rock that played a role in the extinction of the dinosaurs more than 65 million years ago. In 2013, a roughly 60-foot-wide fireball exploded above the Russian city of Chelyabinsk, damaging thousands of buildings and injuring about 1,500 people.

An image captured a few minutes after the intentional collision of NASA’s DART mission with its target asteroid, Dimorphos.



Mr. Johnson said there are alternatives to the kinetic-impactor technique successfully demonstrated by the DART mission, including shooting asteroids with ion beams or changing their trajectories through the use of a so-called gravity tractor—a spacecraft that looms near an asteroid and exerts a gravitational pull on the space rock for an extended time.

“Every situation we may face is a little bit different—time to impact, the size of the object, the orbit—and may require different tools,” he added.

Alan Fitzsimmons, a DART investigation team member and astronomy professor at Queen’s University Belfast, said he would like the gravity tractor technique tested next, “because it’s actually very difficult to accurately guide and maneuver spacecraft in very close proximity to an asteroid.”

“That’s something I certainly think needs to be carefully thought about after DART,” Dr. Fitzsimmons said.

Write to Aylin Woodward at [email protected]

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