Researchers have warned that if the asteroid 2024 YR4 collides with the moon in 2032, it could send lunar debris hurtling towards Earth, posing a risk to satellites and creating a spectacular meteor shower. The asteroid, estimated to be 53-67 metres wide, initially had a 3% chance of hitting Earth, but later observations reduced that to 0.0017%. However, the odds of it striking the moon have risen to 4.3%, according to data from the James Webb Space Telescope.
A study by Canadian researchers, not yet peer-reviewed, simulated the impact, suggesting it would create a 1km-diameter crater on the moon and launch millions of kilograms of debris into space. Some of this material could reach Earth within days, with millimetre- to centimetre-sized rocks burning up in the atmosphere, posing no threat to humans. However, larger fragments could be captured in Earth's orbit, endangering satellites, spacecraft and astronauts.
Dr Paul Wiegert of the University of Western Ontario, lead author of the study, described the impact as 'comparable to a large nuclear explosion in terms of the amount of energy released'. He added that a centimetre-sized rock travelling at tens of thousands of metres per second is 'a lot like a bullet'. The study calls for extending planetary defence considerations to cover threats to areas beyond near-Earth space.
Nasa and other space agencies have long focused on tracking asteroids that could threaten Earth, with the moon being of secondary concern. In 2022, Nasa's Double Asteroid Redirection Test (Dart) successfully altered the orbit of asteroid Dimorphos, demonstrating a potential defence technique. Asteroid 2024 YR4 is now too far to observe and will not be visible again until 2028, when researchers can reassess its size and trajectory.
Earlier concerns that an impact with the moon could alter its orbit around Earth were ruled out by Nasa in April, after reassessing the asteroid's size.
