Roughly five months after intentionally crashing a rocket into a distant asteroid, NASA has some good news: The mission was a smashing success, and similar methods could prevent Earth from being obliterated by planet-killing space rocks in the future, according to four new studies published in the journal Nature.
"I cheered when DART slammed head on into the asteroid for the world's first planetary defense technology demonstration, and that was just the start," Nicola Fox, associate administrator for the Science Mission Directorate at NASA Headquarters, said in a statement. "These findings add to our fundamental understanding of asteroids and build a foundation for how humanity can defend Earth from a potentially hazardous asteroid by altering its course."
NASA launched the Double Asteroid Redirection Test (DART) mission in late November 2021, after five years of planning. The goal was to test a theory of planetary defense called the "kinetic impactor" technique — basically, altering an asteroid's trajectory by crashing a rocket into it at high speed.
In September 2022, NASA's DART spacecraft successfully collided with the asteroid Dimorphos, a 525-foot-wide (160 meters) "moonlet" that orbits a larger asteroid called Didymos, roughly 7 million miles (11 million kilometers) from Earth. The force of the impact altered Dimorphos' orbit around Didymos by about 33 minutes, successfully redirecting the smaller space rock's trajectory, NASA initially reported. (Neither asteroid ever posed a risk to Earth, but the asteroids' size and shared orbit made them ideal targets for the mission.)
Now, four new studies published March 1 confirm that the mission was even more successful than NASA engineers initially predicted — and that the kinetic impactor technique is indeed a viable method for protecting Earth from potentially deadly asteroids in the future.
The first of the new studies reports DART's successful impact with the asteroid in detail, recreating the timeline leading up to the impact, the location and nature of the impact itself, and the size and shape of Dimorphos. The successful impact with the asteroid and the resulting change in Dimorphos' orbit demonstrate that "kinetic impactor technology is a viable technique to potentially defend Earth if necessary," the paper concludes.
The study also notes that intercepting an asteroid roughly the size of Dimorphos is possible without an advance reconnaissance mission, as long as scientists have several years — or preferably several decades — to prepare for the asteroid's approach.
The second study uses two different methods to independently confirm the 33-minute slowdown of Dimorphos' orbit, while the third paper calculates the momentum transferred from the DART spacecraft to the asteroid. The impact instantly slowed the asteroid's orbital speed by at least 0.1 inch per second (2.7 millimeters per second), thanks to both the momentum of the crashing spacecraft and the enormous plume of dust ejected from the asteroid's surface after the crash.
This trail of dusty debris has since been seen stretching into space for thousands of miles, transforming Dimorphos into a little-understood type of asteroid called an "active asteroid" — essentially, a space rock that orbits like an asteroid but sports a tail like a comet, the final paper says. While scientists have previously predicted that active asteroids result from collisions, until now the transformation has never been seen in real time.
Taken together, these results pave the way for "a bright future for planetary defense," Jason Kalirai, the mission area executive for civil space at the Johns Hopkins Applied Physics Laboratory, which co-manages the DART mission with NASA, said in the statement.
In-depth research into the DART collision will continue, as the European Space Agency plans to launch its Hera spacecraft in 2024 to study the scarred face of Dimorphos up close.
