If you’re like every other earthling, you may want to keep your head down on Dec. 22, 2032. That’s the day an asteroid dubbed 2024 YR4 may strike our planet. Cosmic bookmakers don’t make an impact terribly likely. According to NASA, the odds of a collision are just 2.3%. But that nearly doubles the 1.2% risk the U.S. space agency and the European Space Agency (ESA) calculated in late January. Those numbers push the asteroid past the 1% threshold that requires reporting the danger to multiple planetary defense authorities, including the U.S. Office of Science and Technology Policy, the United Nations’ Space Mission Planning Advisory Group, and the U.N.’s Office for Outer Space Affairs.
The space rock does not remotely pose an existential threat to life on Earth. It measures 130 to 300 feet across, a pebble compared to the asteroid that killed the dinosaurs, which is estimated to have been six to nine miles in length. On the other hand, on Feb. 15, 2013, an object that measured just 65 feet across exploded in the skies over Chelyabinsk, Russia, damaging 7,200 buildings and injuring 1,500 people. Astronomers rank the danger an asteroid poses on something known as the Torino Scale, a zero to 10 hazard index that starts with rocks that pose no risk to us at all and runs to those that are “capable of causing global climatic catastrophe that may threaten the future of civilization as we know it.” The asteroid making so much news today ranks as a three, representing “a chance of collision capable of localized destruction.”
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So should you worry? Almost certainly not. For all of the talk about fraying global alliances and the challenge governments have handling crises competently and well, protecting the Earth from incoming ordnance is one area in which political leaders, scientific minds, and public policy makers have their act together. A global web of space agencies, private observatories, and both Earth- and space-based telescopes are keeping a constant watch on the skies, tracking thousands of asteroids that pose even a minimal risk to Earth. What’s more, in the event a space rock does represent a threat, a NASA spacecraft proved in 2022 that the basic technology exists to intercept and deflect it before it comes anywhere near us.
It’s only recently that we became aware of 2024 YR4 at all. The rock was discovered on Dec. 27, 2024, by the NASA-funded Asteroid Terrestrial-Impact Last Alert System (ATLAS) telescope in Chile. The size, trajectory, and speed of the asteroid immediately made it a cause of concern. Not only is it bigger than the Chelyabinsk object and potentially headed for Earth, it is also moving fast—about 38,000 mph, according to NASA’s calculations, or more than twice the velocity of an Earth-orbiting satellite. It’s that screaming speed that causes even a relatively small asteroid to pack such a destructive wallop, since the faster an object moves the more energy it carries—energy that is dissipated when it collides with something like a planet.
The location of 2024 YR4 qualifies it not just as any asteroid, but a near-Earth object (NEO). NEOs are defined as asteroids that hug the inner solar system, where we live, coming within 1.3 astronomical units of the sun. A single astronomical unit is the distance from the sun to the Earth, or 93 million miles.
Once 2024 YR4’s NEO status was established, ATLAS astronomers acted fast, alerting not only the U.S. Office of Science and Technology Policy and the U.N., but the ESA, the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory, and perhaps most important, the International Asteroid Warning Network (IAWN), a consortium of no fewer than 59 governments, national space programs, and observatories that keep their eyes on the skies, cataloguing and tracking the flight paths of hundreds of thousands of asteroids, with special attention paid to the NEOs.
Currently NASA, the IAWN, and other sky-watchers are monitoring about 38,000 NEOs, continually tracking their trajectories to determine if any changes in their flight paths warrant moving them either up or down the Torino Scale. At the moment, 2024 YR4 is close enough to Earth to be easily visible to telescopes. That will change, however, in April, when its flight path carries it around the sun, making it impossible to see until June of 2028. NASA is taking advantage of the time it has left before 2024 YR4 vanishes, reserving observation time on the James Webb Space Telescope—the most powerful off-Earth observatory ever built—to further investigate the rock’s size, mass, and flight path.
Not only can all of these observations help predict when and if an asteroid will strike Earth, it can also provide at least a general range of what the impact point on the planet would be. With roughly 70% of Earth’s surface covered by ocean, that by itself means only a 30% chance a population center will be struck. For now, NASA astronomers have sketched out a very general 2024 YR4 impact zone running from the eastern Pacific Ocean to northern South America, the Atlantic coast of Africa, the Arabian Sea, and South Asia. That’s an awful lot of earthly real estate, but when the asteroid becomes visible again and draws closer to us, a much more precise ground-zero could be determined.
The question, of course, is what do we do if calculations determine that we are in the cosmic cross hairs? With months—even years—to prepare, evacuation of endangered population centers is always possible. In January of 2021, the then-outgoing Trump Administration published a study of NEO emergency protocols, which reached a conclusion, shared by astronomers, that “mitigation measures that can be taken on Earth to protect lives and property include evacuation of the impact area and movement of critical infrastructure.”
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Sheltering in place is also an option, depending on the size of the asteroid and its anticipated destructiveness. A 2024 study in Acta Astronautica concluded that, at least outside of the bullseye of the impact zone, “seeking shelter in the basement of a reinforced concrete building or storm shelter, or in a home-built shelter in the basement of a house would suffice as alternatives to evacuation.” The authors of the paper saw hurricane preparedness measures as a good model for asteroid preparedness.
But humanity does not have to be a passive target. In 2022, NASA launched the Double Asteroid Redirection Test (DART) spacecraft, whose sole goal was to fly 7 million miles to the 525-foot asteroid Dimorphos, and crash into it at 14,000 miles per hour. Dimorphos is a moonlet of the larger 2,560-ft asteroid Didymos, making one revolution around its parent rock every 11 hours and 55 minutes. The purpose of the mission was to see if the impact could change the speed and direction of Dimorphos—a proof-of-principle exercise to determine if the same kind of planned collision could deflect an incoming asteroid. The mission succeeded wildly, accelerating Dimorphos’s orbit by 32 minutes, tripling NASA’s most optimistic projections.
“This mission shows that NASA is trying to be ready for whatever the universe throws at us,” said then-NASA Administrator Bill Nelson when the results were released. “NASA has proven we are serious as a defender of the planet.”
Building a fleet of asteroid-deflecting spacecraft takes time and money, of course, and one mission to one harmless moonlet is a long way from deploying a global, Iron Dome-style anti-asteroid system. Until that hardware is in place, humanity is doing the next best thing, joining hands to scan the skies and sound a timely alert should our collective welfare ever be threatened.
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