Why a NASA spacecraft will crash into an asteroid

Why a NASA spacecraft will crash into an asteroid

Why a NASA spacecraft will crash into an asteroid

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

A spacecraft named Dart will zero in on the asteroid on Monday, intending to hit it head-on at 14,000 mph (22,500 km/h). The impact should be just enough to nudge the asteroid into a slightly tighter orbit around the companion space rock – showing that if a killer asteroid ever heads our way, we’ll have a hell of a chance to deflect it.

Cameras and telescopes will see the crash, but it will take months to determine if it actually changed its trajectory.

The $325 million planetary defense test began with Dart’s launch last fall.


The asteroid with the bull on it is Dimorphos, about 7 million miles (9.6 million kilometers) from Earth. It’s actually the puny sidekick to a 2,500-foot (780-meter) asteroid named Didymos, Greek for twin. Didymos was discovered in 1996 and spins so fast that scientists believe it threw off material that eventually formed a moon. Dimorphos – about 525 feet (160 meters) across – orbits the parent body at a distance of less than 1.2 kilometers.

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

NASA insists there is zero chance either asteroid will threaten Earth – now or in the future. That is why the couple was chosen.


Johns Hopkins took a minimalist approach in developing Dart – short for Double Asteroid Redirection Test – given that it is essentially a battering ram and faces certain destruction. It has a single instrument: a camera used to navigate, aim and chronicle the final action. Thought to be a pile of rocks, Dimorphos will appear as a point of light an hour before impact, looming larger and larger in the camera images beamed back to Earth. Managers are confident that the Dart will not accidentally bump into the larger Didymos. The spacecraft’s navigation is designed to distinguish between the two asteroids and, during the last 50 minutes, target the smaller one.

The size of a small vending machine at 1,260 pounds (570 kilograms), the spacecraft will slam into about 11 billion pounds (5 billion kilograms) of asteroid. “Sometimes we describe it as driving a golf cart into a great pyramid,” Chabot said.

Unless Dart misses — NASA puts the odds of that happening at less than 10% — it will be the end of the road for Dart. If it screeches past both space rocks, it will meet them again in a couple of years for Take 2.


Little Dimorphos completes a lap around big Didymos every 11 hours and 55 minutes. The impact of Dart should shave approx. 10 minutes of it. Although the strike itself should be immediately visible, it will take months to verify the moonlight’s shifted orbit. Cameras on Dart and a mini tagalong satellite will capture the collision up close. Telescopes on all seven continents, along with the Hubble and Webb space telescopes and NASA’s asteroid-hunting Lucy spacecraft, can see a bright flash as Dart strikes Dimorphos, sending streams of rock and dirt hurtling into space. The observatories will track the asteroid pair as they circle the sun, to see if Dart changed Dimorphos’ orbit. In 2024, a European spacecraft named Hera will follow Dart’s journey to measure the impact results.

Even if the proposed nudge will only change the moon’s position slightly, it will add up to a big shift 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,” she said. Even if Dart misses, the experiment will still provide valuable insights, said NASA program manager Andrea Riley. “This is why we are testing. We want to do it now rather than when there is a real need,” she said.


Planet Earth is on an asteroid-chasing roll. NASA has nearly a pound (450 grams) of debris collected from asteroid Bennu on its way to Earth. The storage will arrive next September. Japan was the first to retrieve asteroid samples, achieving the feat twice. China hopes to follow suit with a mission to launch in 2025. NASA’s Lucy spacecraft, meanwhile, is on its way to asteroids near Jupiter, after launching last year. Another spacecraft, the Near-Earth Asteroid Scout, is loaded into NASA’s new lunar rocket awaiting liftoff; it will use a solar sail to fly past a space rock smaller than 18 feet next year. In 2026, NASA will launch a census telescope to identify hard-to-find asteroids that may pose a risk. One asteroid mission is on the ground while an independent review commission considers its future. NASA’s Psyche spacecraft was supposed to launch this year to a metal-rich asteroid between Mars and Jupiter, but the team couldn’t test the flight software in time.


Hollywood has churned out 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 leading an all – 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 of the sci-fi films are more accurate than others, he noted that entertainment always wins. The good news is that the coast seems ready for the next century, with no known threats. Otherwise, “it would be like the movies, wouldn’t it?” said NASA’s science mission manager Thomas Zurbuchen. What is worrying, however, are the unknown threats. Fewer than half of the 460-foot (140-meter) objects have been confirmed, with millions of smaller but still dangerous objects zooming around. “These threats are real, and what makes this time special is that we can do something about it,” Zurbuchen said. Not by blowing up an asteroid like Willis’ character did — that would be a last-minute resort — or by begging government leaders to act like DiCaprio’s character did to no avail. If time permits, the best tactic may be to push the threatening asteroid out of the way, like Dart.


The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. AP is solely responsible for all content.

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