In a first-of-its-kind world-saving experiment, NASA is about to destroy a small, harmless asteroid millions of miles away. The Dart spacecraft will target 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 put the asteroid into a slightly tighter orbit around its companion space rock—showing that if a killer asteroid is ever headed our way, we have a chance to deflect it.
This is the stuff of science fiction books and really corny episodes of Star Trek from when I was a kid, and now it’s real,” NASA program scientist Tom Statler said Thursday. Cameras and telescopes will track the crash, but it will take days or even weeks to determine whether it actually changed its orbit. The $325 million planetary defense test began with the launch of Dart last fall.
ASTEROID TARGET
The target asteroid is Dimorphos, about 7 million miles (9.6 million kilometers) from Earth. It’s actually a tiny sidekick to a 2,500-foot (780-meter) asteroid named Didymos, Greek for twin. Didymos, discovered in 1996, is spinning so fast that scientists believe it threw off the material that eventually formed the marigold. Dimorphos — roughly 525 feet (160 meters) across — orbits its parent body at a distance of less than 1.2 kilometers.
This is really a deflection of the asteroid, not a disruption,” said Nancy Chabot, a planetary scientist and mission team leader at the Johns Hopkins University Applied Physics Laboratory who is leading the effort. “This isn’t going to blow up an asteroid. It’s not going to break into lots of pieces.” Rather, the impact will gouge a crater tens of yards (meters) in size and hurl about 2 million pounds (1 million kilograms) of rock and debris into space. NASA insists there is zero chance the asteroid would threaten Earth – now or in the future.That’s why the pair was chosen.
ARROW, BUMPER
The Johns Hopkins lab took a minimalist approach in developing the Dart — short for Double Asteroid Redirection Test — given that it’s essentially a battering ram and faces certain destruction. It has a single tool: a camera used for navigation, aiming and recording the final action. Dimorphos, which is believed to be essentially a pile of debris, will appear as a point of light an hour before impact and will loom larger and larger in camera images beamed back to Earth. Managers are confident that the Dart will not hit the larger Didymos by accident. The spacecraft’s navigation is designed to distinguish between the two asteroids and target the smaller one in the last 50 minutes.
The probe, about the size of a small vending machine and weighing 1,260 pounds (570 kilograms), will hit an asteroid weighing roughly 11 billion pounds (5 billion kilograms). “We sometimes describe it as driving a golf cart into the Great Pyramid,” Chabot said. If Dart doesn’t miss—NASA estimates that less than a 10% chance it will—it will be the end of the road for Dart. If it flies past both space rocks, it will encounter them again in a few years for Take 2.
SAVING THE EARTH
Little Dimorphos completes a lap around Big Didymos every 11 hours and 55 minutes. It should reduce the impact of the Dart by about 10 minutes. Although the impact itself should be immediately apparent, it may take several weeks or more for the modified moon’s orbit to be verified. Cameras on Dart and the tagalong mini-satellite capture the collision up close.
Telescopes on all seven continents, along with the Hubble and Webb Space Telescopes and NASA’s asteroid-hunting spacecraft Lucy, can see a bright flash as Dart hits Dimorphos, sending streams of rock and dirt cascading into space. Observers will follow the pair of asteroids as they circle the Sun to see if Dart has changed Dimorphos’ orbit. In 2024, Europe’s Hera spacecraft will follow Dart’s path to measure the results of the impact.
Although the intended nudge should change the moon’s position only slightly, Chabot says it will lead to a large shift over time. “So if you wanted to do it for planetary defense, you would do it five, 10, 15, 20 years in advance to make the technique work,” she said.
Even if Dart misses, the experiment will still provide valuable information, NASA program director Andrea Riley said. “That’s why we’re testing.” We want to do it now rather than when it’s actually needed,” she said.
Planet Earth is on its way to asteroids. NASA has nearly 450 grams of debris collected from the Earth-bound asteroid Bennu. The stash should arrive next September. Japan was the first to obtain asteroid samples, which it did twice. China hopes to follow up with a mission launched in 2025. Meanwhile, NASA’s Lucy spacecraft is headed for asteroids near Jupiter after launching last year. Another spacecraft, the Near-Earth Asteroid Scout, is loaded onto a NASA rocket awaiting launch; next year it will use a solar sail to fly past a space rock that is less than 18 meters.
In the next few years, NASA also plans to launch a census telescope that would identify hard-to-find asteroids that could pose a risk. . One asteroid mission is grounded while an independent review board considers its future. NASA’s Psyche spacecraft was supposed to launch to a metal-rich asteroid between Mars and Jupiter this year, but the team couldn’t test the flight software in time.
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