Why would a NASA spacecraft crash into an asteroid?

Illustration of NASA’s DART spacecraft and Italian Space Agency’s (ASI) LICIACube before impact in the Didymos binary system (NASA/JOHNS HOPKINS, APL/STEVE GRIBBEN) (NASA/JOHNS HOPKINS, APL/STEVE GR/ )

In the first experiment of its kind to save the world, NASA is about to hit a harmless little asteroid millions of miles away.

A spacecraft called Dart will head to 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, showing that if a killer asteroid was headed our way, we’d have a chance of deflecting it.

“This is something that shows up in science fiction books and cheesy ‘StarTrek’ episodes 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 find out if it really changed the orbit.

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

NASA Dart Mission infographic


The asteroid with the target is Dimorphos, about 7 million miles (9.6 million km) from Earth. It is actually the traveling companion of a 780 meter asteroid called Didymos, which in Greek means twin. Discovered in 1996, Didymos spins so fast that scientists think it spewed out material that eventually formed a mole. Dimorphos, about 160 meters in diameter, orbits its parent body at a distance of less than 1.2 kilometers.

“This is an asteroid deflection, not a disturbance”explains Nancy Chabot, a planetary scientist and mission team leader at the Johns Hopkins University Applied Physics Laboratory, which is leading the project. “This is not going to blow up the asteroid. He’s not going to put it into many pieces.” Rather, the impact will carve out a crater tens of meters and hurl some 2 million pounds (1 million kilograms) of rock and soil into space.

NASA insists that there is no chance of either asteroid threatening Earth, now or in the future. That is why this pair was chosen.


The Johns Hopkins Laboratory took a minimalist approach to developing Dart (short for Double Asteroid Redirection Test), since he is essentially a battering ram and faces certain destruction. It has a single instrument: a camera that serves to navigate, aim and chronicle the final action. Dimorphos, believed to be essentially a pile of debris, will emerge as a point of light an hour before impact, appearing larger and larger in camera images transmitted to Earth. The managers are confident that Dart will not crash into the larger Didymos by mistake. The ship’s navigation is designed to distinguish between the two asteroids and, in the last 50 minutes, target the smaller one.

The size of a small 570-kilogram vending machine, the ship will crash into an asteroid weighing about 5 billion kilograms. “Sometimes we describe it Like crashing a golf cart into a Great PyramidChabot said.

Unless the Dart fails — NASA puts the odds of that happening at less than 10 percent — it will be the end of the road for the Dart. If you speed past both space rocks, you’ll meet them again in a couple of years for the second shot.

NASA Dart Mission infographic


Little Dimorphos completes one revolution around the great Didymos every 11 hours and 55 minutes. Dart’s impact should reduce that time by about 10 minutes. Although the impact itself should be immediately apparent, it could take a few weeks or more to verify the lunar’s modified orbit. Cameras on Dart and a companion minisatellite 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, will be able to see a bright flash as Dart hits Dimorphos and sends cascading jets of rock and debris. to space. The observatories will follow the asteroid pair as they orbit the Sun, to see if Dart altered Dimorphos’s orbit. In 2024, a European spacecraft called Hera will retrace Dart’s path to measure the results of the impact.

According to Chabot, although the intended push of the moon will only slightly change its position, a major change will occur over time. “So if you’re going to do this for planetary defense, you’d have to do it five, 10, 15, 20 years in advance for this technique to work,” he said. Even if Dart fails, the experiment will provide valuable information, said NASA program executive Andrea Riley. “This is why we do tests. We want to do it now and not when there is a real need,” she said.


Planet Earth is on an asteroid hunting spree. NASA has about half a kilo (450 grams) of debris collected from the asteroid Bennu bound for Earth. The stash should arrive next September. Japan was the first to recover asteroid samples, achieving the feat twice. China hopes to do the same with a mission due to launch in 2025. For its part, NASA’s Lucy spacecraft is headed for near-Jupiter asteroids, following its launch last year. Another spacecraft, the Near-Earth Asteroid Scout, is loaded onto NASA’s new moon rocket waiting to lift off; will use a solar sail to pass in front of a space rock less than 18 meters next year. In the coming years, NASA also plans to launch a census telescope to identify hard-to-find asteroids that could pose a risk. An asteroid mission is grounded as an independent review board weighs its future. NASA’s Psyche spacecraft should have been launched this year toward 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 space rock movies over the decades, such as Armageddonfrom 1998, which brought Bruce Willis to Cape Canaveral for filming, and Don’t Look Up, from last year, with Leonardo DiCaprio leading an all-star cast. NASA planetary defense officer Lindley Johnson reckons he’s seen them all since meteorfrom 1979, his favorite “since Sean Connery played me.” Although some sci-fi movies are more accurate than others, she 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 in the movies, wouldn’t it?” said NASA science mission chief Thomas Zurbuchen. However, what is worrying 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 buzzing around. “These threats are real, and what makes this moment special is that we can do something about it,” Zurbuchen said. Not by blowing up an asteroid, as Willis’s character did—that would be a last-ditch resort—nor by begging government leaders to take action, as DiCaprio’s character did to no avail. If time permits, the best tactic might be to push the threatening asteroid out of our way, like Dart.

By Marcia Dunn

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