In 2025, the threat of a disastrous asteroid impact momentarily heightened when astronomers detected a building-sized asteroid on a collision course with Earth.

Known as 2024 YR4, this asteroid was initially identified by astronomers in late December 2024, with estimates placing its size between 40 and 90 meters. Any potential trajectory through our solar system would intersect a narrow zone that includes Earth, leading astronomers to initially assess a 1 in 83 probability of collision in 2032.

As they monitored the asteroid’s orbit more closely in early 2025, the likelihood of an impact was updated to a concerning 1 in 32 by February.

If it had impacted close to an urban area, the consequences would have been devastating, equivalent to several megatons of TNT. The asteroid was temporarily classified as a 3 on the Turin scale, where 0 means no threat and 10 signifies a global catastrophe. This raised alarms among several United Nations agencies, resulting in coordinated efforts for a global telescope campaign and discussions on the necessity of an asteroid deflection mission.

During this period, global space agencies convened regularly to share observations and enhance understanding of the asteroid. “2024 YR4 proved to be a significant learning experience for us,” stated Richard Moisle from the European Space Agency (ESA). “This served as crucial training to enhance our capabilities related to asteroid detection and understanding the overarching challenges.”

By February 20, astronomers had refined the trajectory of 2024 YR4, effectively removing Earth from the asteroid’s predicted path, and ESA subsequently reduced the collision risk to 1 in 625, or 0.16 percent. Weeks later, both NASA and ESA confirmed that there was no longer any risk of collision. “They are not considered a threat to our planet,” affirmed Moisle.

Nonetheless, astronomers still acknowledge a minor risk of a lunar impact, estimated at about 4% for 2032. “Should we hit the moon, it would provide a unique opportunity to observe the impact process from a safe distance,” commented Gareth Collins from Imperial College London.

Researchers are now assessing the potential ramifications of an asteroid impacting the moon, including the risk of debris cascading toward Earth. They are also exploring the feasibility of a deflection mission and strategizing on how to effectively dispatch a small satellite to an asteroid in an attempt to detonate it with a nuclear device. “We must tread carefully to ensure that a moon impact does not unintentionally lead to an Earth impact,” Rang Moisle.

The present 4 percent chance of a lunar collision is not sufficiently alarming to compel global space agencies to initiate a formal mission. This probability is unlikely to shift soon, as 2024 YR4 is currently obscured by the Sun and won’t be visible until 2028. However, due to its unique positioning in Earth’s orbit, there will be a rare opportunity to observe it with the James Webb Space Telescope in February 2026. Moisle indicated that since planning an asteroid mission can take years, data from these observations will represent the last realistic chance to determine whether a mission to visit or deflect the asteroid is warranted.

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