EXPLAINER: Why a NASA spacecraft will crash into an asteroid

EXPLAINER: Why a NASA spacecraft will crash into an asteroid

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

A spacecraft named Dart will zero in on the asteroid Monday, intent on slamming it head-on at 14,000 mph (22,500 kph). The impact should be just enough to nudge the asteroid into a slightly tighter orbit around its companion space rock — demonstrating that if a killer asteroid ever heads our way, we’d stand a fighting chance of diverting it.

Cameras and telescopes will watch the crash, but it will take months to find out if it actually changed the orbit.

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

ASTEROID TARGET

The asteroid with the bull’s-eye on it is Dimorphos, about 7 million miles (9. 6 million kilometers) from Earth. It is actually the puny sidekick of a 2,500-foot (780-meter) asteroid named Didymos, Greek for twin. Discovered in 1996, Didymos is spinning so fast that scientists believe it flung off material that eventually formed a moonlet. Dimorphos — roughly 525 feet (160 meters) across — orbits its parent body at a distance of less than a mile (1. 2 kilometers). This really is about the asteroid destruction, not disruption,” stated Nancy Chabot (a Johns Hopkins University planetary scientist who is leading this effort). “This isn’t going to blow up the asteroid. It isn’t going to put it into lots of pieces.” Rather, the impact will dig out a crater tens of yards (meters) in size and hurl some 2 million pounds (1 million kilograms) of rocks and dirt into space.

NASA insists there’s a zero chance either asteroid will threaten Earth — now or in the future. This is why they chose the pair.

DART, THE IMPACTOR

Johns Hopkins took a minimalist approach in developing Dart — short for Double Asteroid Redirection Test — given that it’s essentially a battering ram and faces sure destruction. It has a single instrument: a camera used for navigating, targeting and chronicling the final action. Believed to be essentially a rubble pile, Dimorphos will emerge as a point of light an hour before impact, looming larger and larger in the camera images beamed back to Earth. Managers are confident Dart won’t smash into the larger Didymos by mistake. The spacecraft’s navigation is designed to distinguish between the two asteroids and, in the final 50 minutes, target the smaller one.

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

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 goes screaming past both space rocks, it will encounter them again in a couple years for Take 2.

SAVING EARTH

Little Dimorphos completes a lap around big Didymos every 11 hours and 55 minutes. The impact by Dart should shave about 10 minutes off that. Although the strike itself should be immediately apparent, it will take months to verify the moonlet’s tweaked orbit. The collision will be captured up-close by Dart’s cameras and the mini tagalong satellite. Telescopes on all seven continents, along with the Hubble and Webb space telescopes and NASA’s asteroid-hunting Lucy spacecraft, may see a bright flash as Dart smacks Dimorphos and sends streams of rock and dirt cascading into space. The observatories will track the pair of asteroids as they circle the sun, to see if Dart altered Dimorphos’ orbit. In 2024, a European spacecraft named Hera will retrace Dart’s journey to measure the impact results.

Although the intended nudge should change the moonlet’s position only slightly, that will add up to a major 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 in order for this technique to work,” she said. Andrea Riley, a NASA program executive, stated that even if Dart fails, the experiment will still provide valuable insights. This is why we test. She said that they prefer to test now, rather than waiting for an actual need.

ASTEROID MISSIONS GALORE

Planet Earth is on an asteroid-chasing roll. NASA has close to a pound (450 grams) of rubble collected from asteroid Bennu headed to Earth. The stash should arrive next September. Japan is the country that was first to recover asteroid samples. It has done this twice. China hopes to follow suit with a mission launching in 2025. NASA’s Lucy spacecraft, meanwhile, is headed to asteroids near Jupiter, after launching last year. Another spacecraft, Near-Earth Asteroid Scout, is loaded into NASA’s new moon rocket awaiting liftoff; it will use a solar sail to fly past a space rock that’s less than 60 feet (18 meters) next year. In 2026, NASA will launch a census-taking telescope to identify hard-to-find asteroids that could pose risks. One asteroid mission is grounded while an independent review board weighs its future. NASA’s Psyche spacecraft should have launched this year to a metal-rich asteroid between Mars and Jupiter, but the team couldn’t test the flight software in time.

HOLLYWOOD’S TAKE

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’s 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, entertainment always wins out. The good news? There are no threats to the coast for the next century. Otherwise, “it would be like the movies, right?” said NASA’s science mission chief Thomas Zurbuchen. What’s worrisome, though, 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. Zurbuchen stated that “these threats are real” and that there is something we can do about them. Willis did not blow up an asteroid, that would have been a last resort. DiCaprio did it in vain. If time allows, the best tactic could be to nudge the menacing asteroid out of our way, like Dart.

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

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