Why would a NASA spacecraft crash into an asteroid?

Why would a NASA spacecraft crash into an asteroid?

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

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

A spacecraft called Dart will head for the asteroid on Monday, intending to hit it full force at 14,000 mph (22,500 km/h). 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 were heading our way, we would have a chance of deflecting it.

“It’s 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 know if it really changed the orbit.

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


The asteroid with the target is Dimorphos, about 7 million miles (9.6 million km) from Earth. It is actually the travel companion of a 780 meter asteroid called Didymos, which in Greek means twin. Discovered in 1996, Didymos spins so fast that scientists believe 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.

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

NASA insists that there is no chance that either asteroid will threaten Earth, now or in the future. That’s why this pair was chosen.


Johns Hopkins Laboratory has taken a minimalist approach to developing Dart (short for Double Asteroid Redirection Test), for he is essentially a ram and faces certain destruction. He has a single instrument: a camera that is used to navigate, aim and chronicle the final action. Dimorphos, believed to be essentially a pile of debris, will emerge as a bright spot an hour before impact, appearing larger and larger in camera images transmitted to Earth. The managers are confident that Dart won’t crash into the bigger Didymos by mistake. The ship’s navigation is designed to distinguish between the two asteroids and, within 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 around 5 billion kilograms. “Sometimes we describe it Like crashing a golf cart into a big pyramidChabot said.

Unless the Dart fails – NASA rates the chance of that happening at less than 10% – that will be the end of the road for the Dart. If you go past the two space rocks, you will encounter them again in a few years for the second hit.


The small Dimorphos completes a revolution around the large Didymos every 11 hours and 55 minutes. Dart impact should reduce this time by about 10 minutes. While the impact itself should be immediately apparent, verifying the moon’s altered orbit could take a few weeks or longer. Cameras on Dart and a companion minisatellite will capture the collision up close. Telescopes on all seven continents, plus 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 into space. Observatories will track the pair of asteroids orbiting the Sun, to see if Dart has altered Dimorphos’ orbit. In 2024, a European spacecraft called Hera will retrace Dart’s trajectory to measure the results of the impact.

According to Chabot, although the predicted thrust of the moon will only slightly change its position, a major change will occur over time. “So if you want to do this for planetary defense, you’ll 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 manager Andrea Riley. “That’s why we do tests. We want to do it now and not when there is a real need,” he said.


Planet Earth is on the hunt for asteroids. NASA has about half a kilo (450 grams) of debris collected from asteroid Bennu bound for Earth. The stash should arrive next September. Japan was the first to collect asteroid samples, achieving the feat twice. China hopes to do the same with a mission slated for launch in 2025. NASA’s Lucy spacecraft, meanwhile, is heading for asteroids near Jupiter, after launching last year. Another spacecraft, the Near-Earth Asteroid Scout, is loaded onto NASA’s new moon rocket awaiting liftoff; will use a solar sail to sail past a space rock under 18 meters next year. In the coming years, NASA also plans to launch a survey telescope to identify hard-to-find asteroids that may pose a risk. An asteroid mission is scrapped as an independent review board assesses 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 space rock movies over the decades, such as Armageddonof 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 films 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 in the movies, wouldn’t it?” said NASA science mission chief Thomas Zurbuchen. However, what is worrying 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 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’ character did – that would be a last resort – or by begging government leaders to act, as DiCaprio’s character did to no avail. Weather permitting, the best tactic might be to push the menacing asteroid out of our way, like Dart.

By Marcia Dunn

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