NASA launches mission to redirect an asteroid—by striking it with a spacecraft
As the first-ever “full-scale planetary defense test” to deflect a space rock, the DART mission aims to show that protecting Earth from a hazardous asteroid is possible.
An illustration of the DART spacecraft approaching the binary asteroids Didymos and Dimorphos. Image Credit: NASA/Johns Hopkins APL
Today at 1:21 a.m. EST, NASA launched its Double Asteroid Redirection Test (DART) spacecraft in the first-ever “full-scale planetary defense test” to deflect an asteroid, the Agency reports. The craft, built and operated by Johns Hopkins Applied Physics Lab in Laurel, Maryland, is designed to autonomously target and intentionally crash into—at 14,400 miles per hour—an asteroid.
The hope is that by hitting an asteroid destined to collide with Earth, a successor to DART could redirect it away from our planet, preventing impact.
“Planetary defense is about making sure that a rock from space doesn’t send us back to the Stone Age,” DART Program Scientist Tom Statler said in a NASA interview. “And the key parts of planetary defense are, first of all, finding the asteroids that are potentially hazardous to the Earth. And we understand where about 40% of those asteroids are.”
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One of those space rocks is Bennu. In October 2020, more than 200 million miles from Earth, a NASA spacecraft named OSIRIS-REx reached out and grabbed a sample from the spinning-top-shaped asteroid, as scientists believe it may contain essential ingredients to our solar system’s planetary formation. Bennu, which is slightly wider than the Empire State Building is tall, is slowly—and steadily—getting closer to Earth.
At a NASA news conference in August, scientists said that there’s a 1-in-1,750 chance that Bennu will collide with Earth between now and the year 2300, a slight increase from scientists’ previous estimate of 1-in-2,700. (Despite the “now” in this prediction, you and your children, and most likely your grandchildren, will be gone before there’s any possibility of this collision happening, Kenneth Chang reports for the New York Times.)
Bennu isn’t alone. Though the chances of Earth getting hit by an asteroid like the one that ended the era of dinosaurs 66 million years ago are slim, fragments of asteroids, “from pebble-sized to person-sized,” hit Earth every day, NASA writes in a press release. An asteroid larger than about 10 feet in diameter hits Earth about once every year, and there’s about a 1-in-50,000 chance of an asteroid larger than 3,200 feet across hitting Earth every 100 years, Bruce Betts reports for Planetary.org. “This isn’t the sort of thing that we want to address at the last minute,” NASA program scientist Kelly Fast told NOVA in June.
Riding atop a SpaceX Falcon 9 rocket, DART took off Wednesday, November 24 from Space Launch Complex 4 East at Vandenberg Space Force Base in California. Image Credit: NASA/Bill Ingalls
DART is headed to a binary asteroid system that will be within 6.8 million miles from Earth in September 2022. Its target is a 525-foot space rock named Dimorphos, meaning “two forms” in Greek, which orbits the half-mile-wide asteroid Didymos (meaning “twin”), NASA reports.
Because Didymos and its moon come “pretty close to Earth,” Johns Hopkins Applied Physics Lab Systems Engineer Elena Adams told NOVA in June, it’s technically “considered a potentially hazardous” system. But, like Bennu, its chances of striking our planet are incredibly slim. “There’s nothing that we could do to it that will make it a danger to the Earth,” Statler said. Hitting Didymos’ moon Dimorphos, for example, won’t change the trajectory of Didymos, Adams told NOVA.
DART will try to push Dimorphos using a technique called kinetic impact deflection: intentionally crashing into the space rock in a bid to move it. Approximately four hours before impact, DART will become fully autonomous, directing itself toward the tiny moon 60,000 miles away. The goal isn’t to simply move Dimorphos. “The important thing isn’t how far we move the asteroid,” Statler said. “It’s how much we change its speed by.” To determine whether the strike was successful at altering Dimorphos’ velocity, scientists will analyze any changes to its orbit with telescopes back on Earth.
Kinetic impact deflection is one potential method—and the “most technologically mature”—of a few proposed techniques to redirect an object hurtling in space, NASA reports. As NASA scientists continue to investigate asteroid deflection strategies, research teams across the globe aim to discover asteroids that could be potentially hazardous to our planet. Ideally, they’ll identify any space rock “on a collision course with Earth” years in advance, Statler said in a NASA interview, buying time for scientists to redirect its path. The goal is never to destroy an asteroid, Statler said: “We probably wouldn’t be able to do that anyway.”
The chances of an asteroid large enough to cause damage to Earth, but small enough to avoid detection well in advance of its approach, are slim. But that doesn’t discredit DART’s mission, Statler suggested. “We take precautions about low-probability events all the time,” he said. If researchers do happen to spot a dangerous asteroid years in advance, “then a change to its velocity,” Statler said, “can make the difference between an impact on Earth and a safe miss.”
