In their scenario, city had 4-year warning

A 330-800 foot asteroid on a collision course with downtown Los Angeles. Four years to try to stop it—or carry out mass evacuations ahead of certain devastation. That’s not the plot of an unoriginal new movie, but the scenario behind a recent NASA-FEMA exercise, the New York Times reports. Reps from NASA’s Jet Propulsion Laboratory, the Energy Department’s National Laboratories, the Air Force, and the California Governor’s Office of Emergency Services were among those that gathered for the Oct. 25 exercise, which simulated the discovery of an asteroid and the gradual realization that it would hit in 2020. In the simulation, it took from now until November 2017 to determine that there was a 100% probability of the asteroid striking, and that the impact would occur across Southern California or just off it.

Experts presented estimates for population displacement and infrastructure damage, as well as ways to present accurate information to the public, according to NASA’s Jet Propulsion Laboratory. “The high degree of initial uncertainty coupled with the relatively long impact warning time made this scenario unique and especially challenging for emergency managers,” says FEMA National Response Coordination Branch Chief Leviticus A. Lewis. “It’s quite different from preparing for an event with a much shorter timeline, such as a hurricane.” But four years wasn’t long enough to prepare a “deflection mission,” the Timesnotes, meaning that the exercise focused on evacuation scenarios. (NASA has a new detection system searching for threats to Earth.)