When a dangerous asteroid threatens Earth, humanity will have to work together, NASA says

A threatening asteroid could bring Earth's oft-squabbling nations together, at least for a while.

Dealing with a big, dangerous asteroid that appears to have our planet in its crosshairs will require a healthy dose of international cooperation, experts say — and it's best to start thinking about that scenario now, while we have enough time to lay out a potential response framework.

The United Nations (UN) has developed "procedures for responding to tsunamis and other big events," Leviticus "L.A." Lewis, the U.S. Federal Emergency Management Agency (FEMA) detailee to NASA's Planetary Defense Coordination Office (PDCO), said during a press briefing on Thursday (June 20). "But for an asteroid impact, we're thinking the scale of it is going to be such that we actually do need to discuss at this time what it would take for an international response on such a large scale," he added.

Part of that response would involve coordinating evacuations of people in the potential impact zone, which would likely cover a large swath of ground, given how fast asteroids move through space and how difficult it is to nail down a newfound asteroid's trajectory. (Small uncertainties in that calculated path would result in big differences in the projected impact point on Earth . And newfound space rocks are the ones to worry about; none of the big asteroids we already know about pose a threat to our planet for the foreseeable future.)

"If we talk about multiple nations and people having to move around, and responding to a very large area, that could be a challenge," Lewis said. "We need to organize and start discussing what it would really take to coordinate a large effort. And who would be in charge? What organization? How would we set it up? Would it be the U.N.? Would it be a combination of international organizations? How would we actually accomplish that? So, that's the new challenge."

Lewis was discussing the results of the fifth Planetary Defense Interagency Tabletop Exercise, an asteroid-threat simulation that was held April 2 and April 3 at the Johns Hopkins Applied Physics Laboratory (APL) in Maryland.

The exercise — the fifth of its kind that researchers have performed, following similar efforts in 2013, 2014, 2016 and 2022 — aimed "to inform and assess our ability as a nation to respond effectively to the threat of a potentially hazardous asteroid or comet ," NASA officials said in a statement .

The participants — nearly 100 people from various U.S. federal agencies and international institutions — considered the following hypothetical scenario: Scientists just discovered a relatively large asteroid that appears to be on an Earth-impacting trajectory. There's a 72% chance it will hit our planet on July 12, 2038, along a lengthy corridor that includes major cities such as Dallas, Memphis, Madrid and Algiers.

But this is just an initial snapshot, with many key facts still fuzzy or unknown. For example, it's unclear how big the asteroid is; its estimated size range is 200 feet to 2,600 feet (60 to 800 meters). And researchers don't know its composition, which is a very important detail; a dense metallic or stony asteroid would behave quite differently — both during a potential deflection attempt and upon impact — than a "rubble pile" of dirt and gravel like Bennu , the space rock that NASA's OSIRIS-REx probe visited and sampled a few years ago.

"The uncertainties in these initial conditions for the exercise allowed participants to consider a particularly challenging set of circumstances," Lindley Johnson, planetary defense officer emeritus at NASA Headquarters in Washington, said in the same statement. "A large asteroid impact is potentially the only natural disaster humanity has the technology to predict years in advance and take action to prevent."

Related: Potentially dangerous asteroids (images)

More knowledge about the newfound space rock won't be forthcoming for a while: The exercise stipulated that it just disappeared behind the sun from Earth's perspective, making further telescope observations impossible for the next seven months.

The participants in the April exercise — which was organized by the PDCO and FEMA, with help from the U.S. Department of State Office of Space Affairs — talked through the potential next steps.

They examined three main near-future possibilities, one of which was to do nothing until more telescope observations can be made. The other two were to start studying, and possibly even developing, a fact-finding mission to the threatening space rock — either a flyby or a more involved, purpose-built rendezvous effort, which would sidle up to the asteroid for a lengthy stretch.

The flyby would likely cost between $200 million and $400 million. The rendezvous mission's price tag would be steeper — in the neighborhood of $800 million to $1 billion.

Most of the exercise's senior leaders favored options two or three "but noted [that] political realities would limit immediate action," states an initial report about the simulation, which you can find here .

— Planetary defense: Protecting Earth from space-based threats

— Deflecting killer asteroids away From Earth: How we could do it

— This is what would happen if scientists found an asteroid heading to Earth

That report includes a selection of comments from anonymous exercise participants. "The most important item of the morning was the discussion involving the political nature of the decision making," one such comment read.

Another highlighted the global nature of the challenge, as Lewis did: "International involvement early will be critical. That credibility is essential and must be established now."

The exercise didn't result in any ironclad rules that must be followed when a threatening asteroid is discovered. (And planetary defense experts say this is indeed a matter of "when" rather than "if;" at some point, a big space rock will head our way.) But no such prescriptions were expected; rather, the main goal was to talk through the possibilities and gain more familiarity with the steps the scientific and international community would take to deal with an incoming asteroid.

"The actual plan, the specific exercise results, aren't really anything," Johnson said in Thursday's briefing. "It's the actual going through the process of doing the planning and working together, communicating and working with each other, that is the real purpose of this exercise."