Astronomers weigh nuclear option to stop Moon-bound asteroid

Late in 2024, a small asteroid stirred astronomers. Discovered on December 27, the asteroid rock—since christened 2024 YR4—was first thought to pose a threat to collide with Earth. Early estimates put it at a 3 percent chance of impacting our world in December 2032, one of the highest probabilities ever recorded for an asteroid just discovered.

The threat was dismissed within weeks. But another crisis situation soon emerged. By May 2025, new calculations showed about a 4 percent chance that YR4 would collide with the Moon.

It measures about 60 meters across, roughly the equivalent of a 10-story building. That may sound small in comparison to the giants that once remade our world, but it is large enough to create some major problems. Astronomers used the James Webb Space Telescope to accurately determine its size on March 26, 2025, with just a seven-meter error margin.

If YR4 were to impact the Moon, it would create a crater nearly a kilometer in diameter. The Moon would still orbit Earth normally, but the impact could eject more than 100 million kilograms of material into space. Some of that would return to Earth in a matter of days and populate near-Earth orbit with high-velocity debris. Effectively, a sudden micrometeoroid storm would increase background risk in space by a factor of a thousand.

Such an event would not threaten life on Earth directly, but the consequences for technology could be devastating. Satellites that guide navigation, communication, and weather forecasting might be crippled. Even astronauts aboard the International Space Station could face life-threatening risks.

As one research team put it in a study now under review for the Journal of the Astronautical Sciences: “We’re not worried about the Moon’s orbit changing. We’re worried about what happens to Earth’s satellites afterward.”

Stopping YR4 is a challenge unlike any before. In 2022, NASA successfully shifted the orbit of a small asteroid moonlet during its Double Asteroid Redirection Test, known as DART. That mission proved that a high-speed impactor could nudge a rock just enough to alter its path.

But repeating that feat here may not be possible. Timing is the issue. The earliest a reconnaissance mission can be dispatched to orbit YR4 and get close-up observation is 2028, allowing merely three years to plan, build, and launch a deflection mission.

No planetary defense endeavor has ever been run on such a compressed schedule. Worse, with no precise measurement of the asteroid's mass and composition, even a precisely aimed impact might not nudge it into its new path as planned. A small miscalculation in math could actually send YR4 into a gravitational keyhole—a narrow tube in space that would have it taking a future crash course for the Earth or the Moon decades from now.

Because of those variables, researchers at NASA's Goddard Space Flight Center, Johns Hopkins University Applied Physics Laboratory, Jet Propulsion Laboratory, Los Alamos National Laboratory, and others concluded deflection is not feasible.

That leaves one possibility that sounds like something out of a Hollywood movie: blowing up the asteroid. Scientists call it robust disruption. The idea is to break YR4 apart into fragments smaller than 10 meters in diameter and then fire each one off so fast that they can't re-aggregate or strike a target in one clump.

There are two plans. One is kinetic disruption, in which a large spacecraft would crash into YR4 at phenomenal speeds. The other is nuclear disruption, in which one or more nuclear bombs would be detonated in order to shatter the asteroid into many small, harmless pieces.

Nuclear disruption might be the best bet. The study hypothesizes a two-nuclear-devices scenario, each with a yield of approximately 100 kilotons—five to eight times the Hiroshima and Nagasaki bombing capability. The at least 2,000-kilogram spacecraft would make the trip to the asteroid approximately 30 days before the disruption date. One would detonate on or near the surface of the asteroid, and the other would be maintained as standby reserve. If left unused, it can be detonated in space safely.

The launch window for such a mission is late 2029 to late 2031. That gives around five to seven years of planning—ambitious, but achievable compared to the ten years effort on DART.

It is not so simple to blow up an asteroid. If YR4 were broken into large pieces instead of small pieces, the fragments could still hit the Moon or even be deflected back toward Earth. The answer is to ensure that the debris cloud disperses very widely, spreading the pieces out so they are no longer dangerous.

Precise modeling of the structure of the first asteroid is important. Rubble piled loosely or a hunk of solid rock would initially respond differently. That is why scientists still push for reconnaissance flights in 2028, even if the YR4 lunar threat is subsequently removed. The information gathered would be applied to fine-tune models not only for this asteroid but for countless others that may arise in the future.

Astronomers continue to emphasize that the likelihood of YR4 impacting the Moon is low—about 96 percent for a miss. Already, though, the asteroid has provided a useful test case. It forced scientists to consider strategy beyond simple deflection and to prepare for those situations in which interruption is the only option.

While the story may remind one of the 1998 film Armageddon, the real mission would be very different. There would be no human crew drilling into a boulder. It would be a robot mission carefully carried out based on precise engineering and international cooperation.

NASA Goddard Space Flight Center's Brent W. Barbee and coauthors emphasize that proving readiness is the real goal. Later discoveries will afford less time to respond. Pretesting reconnaissance, deflection, and disruption strategies beforehand assures that humanity will not be caught off guard.

Research findings are available online in the Journal of the Astronautical Sciences.

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