The risk of a large asteroid, once considered a threat to the moon, is no longer a concern. Discovered in late December 2024, asteroid 2024 YR4 initially had up to a 3.1% chance of hitting Earth by December 22, 2032. But after extensive observations, that threat was ruled out. By June 2025, scientists speculated there was a 4.3% chance the asteroid could instead collide with the moon.
If YR4 were to hit the moon, Earth would remain safe. However, any astronauts or structures on the lunar surface could be at risk, as could the satellites we rely on for navigation and communication.
To assess the risk of a lunar impact, astronomers initially expected to wait until 2028, when YR4 would become visible again. However, Dr. Andy Rivkin from Johns Hopkins University and Julien de Wit from MIT seized a chance for earlier observations. They got permission to use the James Webb Space Telescope, which offered a unique opportunity to track the asteroid.
Their observations, conducted in February, showed that instead of colliding, YR4 would pass by the moon at a distance of about 14,229 miles (22,900 kilometers). This means we won’t experience a dramatic lunar impact that would have captured the world’s attention.
Dr. Rivkin and Dr. de Wit’s efforts underscore how powerful telescopes can help mitigate potential space threats. Their methods for tracking such faint objects could be beneficial for future asteroid risks. YR4, measuring around 60 meters (200 feet) wide, is a compact target among countless stars, making it a challenge to observe.
In the past, Webb has successfully detected large celestial bodies and faint asteroids. For instance, in December 2024, it discovered 138 new asteroids, highlighting its ability to see into the depths of the solar system.
Despite initial concerns about YR4, the latest studies have provided a more accurate view of its trajectory. Dr. Paul Wiegert, an astronomy professor, remarked that while he was disappointed not to observe a lunar impact, the work shows the incredible capabilities of current science and technology to navigate future threats effectively.
These new findings illustrate the importance of ongoing observations to improve our understanding of asteroids and reduce uncertainties about their paths. As Dr. de Wit noted, “Every time we observe an asteroid, we narrow down the possible trajectories.” This approach will serve as a foundation for NASA’s future planetary defense initiatives, ensuring we’re prepared if another potential threat arises.
For further details on space defense efforts, check out NASA’s planetary defense resources here.
