An asteroid is headed toward a close approach to Earth on December 22, 2032. But fear not, the Webb Space Telescope just re-confirmed that asteroid 2024 YR4 has a nearly 0% probability of crashing into Earth. That said, astronomers are unable to rule out a possible impact with the Moon.
The Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile discovered the asteroid on December 27, 2024. Shortly after its discovery, asteroid 2024 YR4 was deemed potentially hazardous, with the odds of it striking Earth reaching nearly 3%. Those odds aren’t massive, but when it comes to the potential threat of a city-killer asteroid, ideally you want them to be closer to a zero-chance probability. On February 20, NASA removed 2024 YR4 from its naughty list after calculations showed that the asteroid had a near-zero chance of hitting Earth.
Phew. The news gets even better—new observations from Webb double down on the confirmation: the asteroid poses no threat to Earth. As for the Moon, that’s apparently another matter.
When it was first spotted, asteroid 2024 YR4 was 515,116 miles (829,000 kilometers) away from Earth. Since then, the space rock has moved away from us, and its next close approach won’t be until December 2028. Ground-based telescopes from the International Asteroid Warning Network have been tracking the asteroid, but it will be too faint to observe until June 2028, according to NASA. That’s why Webb was called in for the job, measuring the asteroid’s brightness across a range of infrared wavelengths to better determine its size.
In late January, a team of scientists proposed using the mid-infrared instrument on Webb to observe the asteroid and better understand its damage potential. The team recently released the preliminary results of Webb’s observations of asteroid 2024 YR4, suggesting that, while the asteroid is larger and rockier than previous observations, it has nearly a 0% chance of hitting Earth during its upcoming flyby. The results have not yet been submitted for peer review and publication.
Webb first spotted the asteroid on March 26, observing it as it rotated every 20 minutes over a five-hour-long period. Using Webb’s observations, the researchers determined that the asteroid was slightly larger than previously believed. Initial estimates suggested that the asteroid measures between 130 and 300 feet wide (40 and 90 meters) based on its reflected light. Webb’s observations, however, measure the asteroid at 200 feet (60 meters) wide.
The recent observations also suggest that the surface of the asteroid is cooler than most other asteroids of its same size and distance from the Sun, which may be because asteroid 2024 YR4 is rockier than usual. The team will use Webb to observe the asteroid again in May to help refine its thermal and orbital properties.
Webb’s observations may have ruled out an Earth impact in seven years, but the results suggest that the asteroid “continues to have a non-zero probability of impacting the Moon at this time,” the researchers concluded. The Moon has likely endured thousands of asteroid impacts during its 4.5-billion-year history, but it’s not yet clear what would happen if asteroid 2024 YR4 strikes our natural satellite. At its current size estimate, the asteroid would likely release about 8 megatons of energy during impact—which is more than 500 times the energy released by the atomic bomb dropped on Hiroshima in 1945, and comparable to the energy released in the Tunguska blast of 1908, according to NASA.
The potential Moon impact would allow scientists the rare opportunity to observe a lunar crater being formed right before their eyes (assuming it hits within our view from Earth), and gain a better understanding of the violent history of the solar system.
English (US) ·