Why Is A NASA Spacecraft Crashing Into An Asteroid?

CAPE CANAVERAL, Fla. (AP) – In the first experiment of its kind to save the world, NASA is about to attack a small, harmless asteroid millions of miles away.

A spacecraft called Dart will focus on the asteroid on Monday, intending to hit it head-on at 14,000 mph (22,500 kph). The impact should be enough to push the asteroid into a slightly tighter orbit around its companion space rock, proving that if a killer asteroid were headed our way, we’d have a fighting chance of deflecting it.

“This is science fiction books and really cheesy episodes of ‘StarTrek’ from when I was a kid, and now it’s real,” NASA program scientist Tom Statler said Thursday.

Cameras and telescopes will observe the crash, but it will take days or even weeks to figure out if it actually changed orbit.

The $325 million planetary defense test began with the launch of Dart last fall.


The bull’s-eye asteroid above it is Dimorphos, about 7 million miles (9.6 million kilometers) from Earth. It’s actually the little companion to a 2,500-foot (780-meter) asteroid called Didymos, Greek for twin. Discovered in 1996, Didymos spins so fast that scientists believe it threw up material that eventually formed a moon. Dimorphos, about 525 feet (160 meters) in diameter, orbits its parent body at a distance of less than a mile (1.2 kilometers).

“It’s really about asteroid deflection, not disruption,” said Nancy Chabot, a planetary scientist and mission team leader at Johns Hopkins University’s Applied Physics Laboratory, which is managing the effort. “That’s not going to blow up the asteroid. It’s not going to put it in a lot of pieces.” Rather, the impact will unearth a crater tens of meters (meters) in size and hurl about 2 million pounds (1 million kilograms) of rock and dirt into space.

NASA insists there is zero chance an asteroid will threaten Earth, now or in the future. That’s why the couple was chosen.

Asteroid Impact Explainer
Asteroid Impact Explainer


The Johns Hopkins lab took a minimalist approach in developing Dart, short for Double Asteroid Redirection Test, since it is essentially a battering ram and faces certain destruction. It has a single instrument: a camera that is used to navigate, orient and chronicle the final action. Thought to be essentially a pile of debris, Dimorphos will emerge as a point of light an hour before impact, growing larger in camera images beamed back to Earth. Managers are confident that Dart will not collide with the larger Didymos by mistake. The spacecraft’s navigation is designed to distinguish between the two asteroids and, in the last 50 minutes, target the smaller one.

About the size of a small vending machine at 1,260 pounds (570 kilograms), the spacecraft will crash into an approximately 11 billion pound (5 billion kilogram) asteroid. “Sometimes we describe it as driving a golf cart into a Great Pyramid,” Chabot said.

Unless Dart is lost, NASA estimates the odds of that happening at less than 10%, it will be the end of the road for Dart. If he screams past the two space rocks, he’ll find them again in a couple of years for Take 2.


Little Dimorphos completes one lap around Big Didymos every 11 hours and 55 minutes. Dart impact should shave about 10 minutes off that. While the strike itself should be immediately apparent, it could take a few weeks or more to verify the moon’s tight orbit. The Dart’s cameras and a tagalong mini-satellite will capture the collision up close. Telescopes on seven continents, along with the Hubble and Webb space telescopes and NASA’s asteroid-hunting Lucy spacecraft, can see a bright flash as Dart slams into Dimorphos, sending streams of rock and dirt cascading into space . The observatories will follow the pair of asteroids as they circle the sun, to see if Dart altered Dimorphos’ orbit. In 2024, a European spacecraft called Hera will retrace Dart’s journey to measure the results of the impact.

Although the predicted boost should only slightly change the moon’s position, it will make a big change over time, according to Chabot. “So if you were going to do this for planetary defense, you would do it five, 10, 15, 20 years in advance for this technique to work,” he said. Even if Dart fails, the experiment will still provide valuable insight, said NASA program executive Andrea Riley. “That’s why we do testing. We want to do it now and not when there’s a real need,” he said.


Planet Earth is chasing asteroids. NASA has about a pound (450 grams) of debris collected from the asteroid Bennu that was headed for Earth. The neckline should arrive next September. Japan was the first to recover asteroid samples, achieving the feat twice. China hopes to follow suit with a mission to launch in 2025. Meanwhile, NASA’s Lucy spacecraft is headed for asteroids near Jupiter, after launching last year. Another spacecraft, Near-Earth Asteroid Scout, is loaded onto NASA’s New Moon rocket awaiting liftoff; will use a solar sail to fly past a space rock that is within 60 feet (18 meters) next year. In the coming years, NASA also plans to launch a census telescope to identify hard-to-find asteroids that may pose risks. An asteroid mission is grounded as an independent review board weighs its future. NASA’s Psyche spacecraft was supposed to launch this year to a metal-rich asteroid between Mars and Jupiter, but the team was unable to test the flight software in time.


Hollywood has produced dozens of killer space rock movies over the decades, including 1998’s “Armageddon,” which brought Bruce Willis to Cape Canaveral for filming, and last year’s “Don’t Look Up” with Leonardo DiCaprio at the head of a star cast. NASA planetary defense officer Lindley Johnson figures he’s seen them all since 1979’s “Meteor,” his personal favorite “since Sean Connery played me.” While some sci-fi movies are more accurate than others, he noted, entertainment always wins. The good news is that the coast looks clear for the next century, with no known threats. Otherwise, “it would be like the movies, wouldn’t it?” said NASA’s science mission chief Thomas Zurbuchen. What is worrying, however, are the unknown threats. Less than half of the 460-foot (140-meter) objects have been confirmed, with millions of smaller but still dangerous objects zooming in. “These threats are real and what makes this time special is that we can do something about it,” Zurbuchen said. Not blowing up an asteroid like Willis’ character did, that would be a last-minute resort, or begging government leaders to act like DiCaprio’s character did in vain. Weather permitting, the best tactic might be to get the threatening asteroid, like Dart, out of our way.

The Associated Press Department of Health and Science is supported by the Department of Science Education at the Howard Hughes Medical Institute. The AP is solely responsible for all content.

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