Don't panic it was just a test.
A make-believe asteroid 200 feet wide just plowed into a simulated New York City, sent there by NASA as part of an exercise to study what might happen if astronomers found a giant space rock heading toward Earth.
If the collision had been real, the city would have been hit with a force 1,000 times more powerful than the nuclear bomb dropped on Hiroshima, leveling buildings from Central Park to lower Manhattan and causing up to 1.3 million deaths.
The fictional cataclysm was the culmination of a weeklong "tabletop exercise" conducted at the biennial Planetary Defense Conference, which was held in Washington last week. The conference attracted dozens of astronomers, academics and disaster experts who were eager to understand how the authorities might react to news that a killer asteroid was headed our way and to what extent space missions and evacuation plans might mitigate the damage.
Scientists said the city might have been spared had there been more than eight fictional years to plan space missions to knock the asteroid off course from Earth.
"I think the exercise illustrated how time is the most valuable asset when it comes to asteroid hazards," said Richard Binzel, a professor of planetary science at the Massachusetts Institute of Technology and a participant in the simulation. "In reality, having many decades of warning gives us multiple options and multiple tries to prevent catastrophe."
Just how likely is it that an asteroid big enough to cause serious damage will hit Earth in real life? Scientists say we can expect one about once every 60 years. While asteroid hunters are confident they've found nearly all the asteroids as big as the one that wiped out the dinosaurs 65 million years ago, there are an estimated 25,000 near-Earth asteroids as big as the asteroid used in the simulation and we don't know where roughly two-thirds of those are.
Of course, the odds that a killer asteroid will smash into one of the world's biggest metropolises, rather than the ocean or a less-populated region, are much smaller but the scientists who created the scenario just couldn't help themselves.
"We could have made it land in Youngstown, Ohio, or Lincoln, Nebraska, or Fairfield, Iowa," said Mark Boslough, a University of New Mexico physics professor who helped organize the simulation. "But that's not as interesting as New York."
The five-day asteroid simulation took as its starting point the make-believe discovery on March 26 of an oblong asteroid as wide as a city block, with a 1-in-10 chance of striking Earth in 2027. Each day of the conference, NASA advanced the clock by months or years, and updated the simulation based on the decisions made by smaller groups of scientists and other experts.
After a make-believe reconnaissance spacecraft launched in 2021 determined that the asteroid was on a direct course for Denver, NASA and the space agencies of Europe, Russia, China and Japan built and launched six equally fictitious spacecraft to slam into the asteroid in 2024 and knock it off course.
This so-called kinetic impactor technique, which NASA will test for real in 2022 with a mission called the Double Asteroid Redirection Test (DART), is just one potential method of deflecting a dangerous asteroid. Other possibilities include tugging on an asteroid using the gravity of a nearby spacecraft, blasting it with nuclear weapons or sending a spacecraft to paint it white to change the amount of solar radiation it absorbs and thereby cause a shift in its trajectory.
The fictional fleet of kinetic impactors hit their mark and pushed the asteroid off course. But the effort knocked off a 200-foot-wide fragment that continued toward Earth. NASA's calculations showed that the object would hit somewhere along a band of land stretching from Nebraska to the Atlantic Ocean. Ten days before impact and on the last day of the conference astronomers announced that the asteroid fragment would make a direct hit on Central Park, in the heart of Manhattan.
As the conference experts considered the logistics of evacuating 10 million people from the New York City metropolitan area a densely populated metropolis bottlenecked by bridges and tunnels they were quickly overwhelmed.
"This is a disaster of unprecedented proportion," said Clark Chapman, a senior scientist at the Southwest Research Institute in Boulder, Colorado. "There are evacuation plans that exist for New York City right now but not to perhaps this scale."
If a dangerous asteroid were actually headed toward the U.S., and efforts to deflect or destroy it were unsuccessful, NASA would work with FEMA to help it understand what kind of damage to expect.
"Whether it's 30 years away, or seven years away, or 30 minutes away, our information sharing with NASA is pretty seamless," said Josh Dozor, FEMA deputy assistant administrator for response.
FEMA, in turn, would keep citizens up to date through the Integrated Public Alert & Warning System (IPAWS), which allows local and federal authorities to send alerts through smartphones and TV broadcasts. Evacuations, if necessary, would be ordered by local governments, and FEMA would help by supplying fuel, clearing evacuation routes and sheltering evacuees, Dozor said.
Of course, the best asteroid defense is finding and deflecting dangerous space rocks before they ever reach Earth, said Mika McKinnon, a disaster expert who has consulted for both NASA and FEMA.
"By the time you're in response and recovery, you've kind of already missed the boat," she said. "It's one of the very few natural disasters that is completely preventable if we're just willing to spend the resources on it."
In a "lessons learned" session at the end of the conference, attendees agreed that more space missions are needed to help scientists discover and study potentially dangerous asteroids. They formally endorsed a proposed asteroid-hunting space telescope called NEOCam, and urged the world's space agencies to send a spacecraft to visit asteroid Apophis, which in 2029 will narrowly miss Earth by 19,000 miles, closer than some satellites.