The impact of a large asteroid with our planet is very unlikely, but that doesn’t mean we shouldn’t be prepared.

NASA and the Federal Emergency Management Agency (FEMA) had their third exercise to simulate how the two agencies should approach and lead the US response in such an event.

“It’s not a matter of if – but when – we will deal with such a situation,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington, in a statement. “But unlike any other time in our history, we now have the ability to respond to an impact threat through continued observations, predictions, response planning and mitigation.”

The event had planetary scientists discuss how to best collect, analyze, and share the data in a scenario where we discover an asteroid on a collision course with our planet. They imagined that a fictitious asteroid 100 to 250 meters (328 to 820 feet) in diameter had a 2 percent probability of impacting our planet on September 20, 2020.

The scenario evolved dramatically. By May 2017, the impact probability became 100 percent, with the bolide hitting somewhere between Southern California and the Pacific (known by November 2019). The previous two exercises discussed a deflecting mission, but this scenario was set up to make the timescale too short for NASA to prepare and launch a space mission.

The teams looked at how best to relocate the population of metropolitan areas like Los Angeles as well as many other cities along the coast. They looked at how infrastructures could be affected as well as the potential data that might be available to scientists at the time.

“The high degree of initial uncertainty coupled with the relatively long impact warning time made this scenario unique and especially challenging for emergency managers,” said 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.”

It was not just the technical challenges they were concerned with. The two agencies looked at how to best inform the public of the dangers, and even how to counteract the spread of rumors and false information.

“We receive valuable feedback from emergency managers at these exercises about what information is critical for their decision making, and we take that into account when we exercise how we would provide information to FEMA about a predicted impact,” said NASA Planetary Defense Officer Lindley Johnson.

The agencies would like to expand future exercises with local and state representatives, as well as management agencies and private sector groups. The exercises are invaluable in preparing for the worst, but hopefully they will never have to be put into practice.