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Imagine if scientists discovered a giant asteroid with a 72 percent chance of hitting the Earth in about 14 years — a space rock so big that it could not only take out a city but devastate a whole region.

This is the hypothetical scenario that asteroid experts, NASA workers, federal emergency management officials, and their international partners recently discussed as part of a table-top simulation designed to improve the nation’s ability to respond to future asteroid threats, according to a 

“Right now we don't know of any asteroids of a substantial size that are going to hit the Earth for the next hundred years,” says 

, the planetary defense section supervisor at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.

“But we also know,” says Daly, “that we don't know where most of the asteroids are that are large enough to cause regional devastation.”

Astronomers estimate that there are roughly 25,000 of these “near-Earth objects” that are 140 meters across or larger, but only about 43 percent have been found to date, according to 

 prepared for the table-top exercise, held in April in Laurel, Md.

This event was just the latest in a series of drills that planetary defense experts have held every couple of years to 

 how they’d handle news of a potentially planet-menacing asteroid — and it’s the first since NASA’s DART 

, which showed that ramming a spacecraft into an asteroid could change its path through space.

This time around, just after the fictional asteroid’s discovery, scientists estimated its size to be anywhere from 60 meters to almost 800 meters across.

Even an asteroid on the smaller end of that range could have a big impact, depending on where it hit the Earth, says 

, NASA’s Planetary Defense Officer Emeritus.

While “a 60-meter asteroid impacting somewhere in the middle of the ocean” wouldn’t be a real problem, he says, the same asteroid hitting land near a metropolitan area would be “a serious situation.”

Because telescopes would see such an asteroid as just a point of light in space, says Daly, “we're going to have very large uncertainties in the asteroid's properties, and that leads to very large uncertainties in what the consequences would be if it were to hit the ground, as well as large uncertainties in what it would take to stop that asteroid from hitting the ground.”

What’s more, this particular scenario unnervingly stipulated that scientists wouldn’t be able to learn more about this threat for more than six months, when telescopes could spot the asteroid again and do another assessment of its trajectory.

Exercise participants discussed three options: simply waiting and doing nothing until those next telescope observations; starting a U.S.-led space mission to have a spacecraft fly by the asteroid to get more information; or creating an effort to build a more expensive spacecraft that would be capable of spending time around the asteroid and possibly even changing its path through space.

Unlike previous asteroid-threat simulations, this one did not play out to a dramatic ending. “We actually stayed stuck in one moment in time for the duration of the exercise. We didn't fast-forward,” says Daly.

As a result, attendees had plenty of time to discuss how to communicate both the uncertainties and the urgent need to act. They also discussed how funding and other practical considerations might play into the decision-making processes in federal agencies and Congress.

Daly says in previous discussions, technical experts tended to assume that access to funding wouldn’t be an issue in such an unprecedented situation, but “the reality is, absolutely, cost was a concern and a factor.”

NASA’s report on the exercise notes that “many stakeholders expressed that they would want as much information about the asteroid as soon as possible but expressed skepticism that funding would be forthcoming to obtain such information without more definitive knowledge of the risk.”

While representatives from space institutions had a clear preference for quickly taking action, “what would political leaders actually do?” says Daly. “That was really an open question that lingered throughout.”

Getting some kind of spacecraft ready, finding the right launch window for it, and having it travel through space to an asteroid “eats up a decade of time pretty fast,” says Johnson. “So that is certainly a concern, looking at it from the technological standpoint.”

But something like 14 years of advance notice will seem like tons of time to emergency managers and disaster responders, says 

, a Federal Emergency Management Agency employee assigned to work with NASA.

Lewis notes that emergency managers would have to think about devoting resources to this seemingly far-off threat while also responding to more immediate hazards like tornadoes and hurricanes. “It’s going to be a particular challenge,” he says.

In the meantime, NASA is on track to launch a new asteroid-finding 

“We’ve got to discover what’s out there, determine their orbits, and then determine whether they represent an impact hazard to the Earth over time,” he says. 

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NASA and other federal agencies recently did a tabletop simulation of an Earth-threatening asteroid to see how they'd handle it.

Asteroid headed toward Earth? NASA simulation explores how the nation might respond

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