Asteroid once feared to hit Moon won't crash after all
What's the story
The James Webb Space Telescope has confirmed that asteroid 2024 YR4 will not collide with the Moon in 2032. The celestial body, which was earlier thought to have a 4.3% chance of hitting our lunar companion, will instead pass safely at an altitude of over 21,000km. Researchers at the Johns Hopkins University Applied Physics Laboratory (JHUAPL) arranged for JWST observations and worked with several teams to refine the orbit and rule out a lunar impact.
Initial fears
Initial predictions indicated potential impact on Earth
Discovered on December 27, 2024, by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS), asteroid 2024 YR4 was initially considered a potential threat. With a diameter of about 60m, it posed a risk of impacting Earth on December 22, 2032. Such an event could have destroyed a city or caused catastrophic tsunamis if it struck the ocean.
Orbit refinement
Uncertainty about lunar impact
While it was confirmed that asteroid 2024 YR4 would miss Earth, its potential lunar impact remained uncertain. This was due to the lack of precise knowledge about its orbit around the Sun. However, between February 18-26 this year, JHUAPL researchers seized an opportunity for the James Webb Space Telescope (JWST) to observe asteroid 2024 YR4 against a faint field of stars whose positions have been accurately measured by ESA's Gaia mission.
Tracking challenge
JWST tracks asteroid's motion against stars
The JWST tracked the motion of asteroid 2024 YR4 against the stars, refining its orbit with high precision. Despite being one of the faintest targets ever observed by JWST, this was no easy task due to the telescope's Near-Infrared Camera having a field of view of just 2.2 square arcminutes. The successful tracking was a joint effort between JHUAPL scientists, the space telescope's engineers, the European Space Agency's Near-Earth Object Coordination Centre, and NASA's Center for Near-Earth Object Studies.
Close pass
Asteroid to pass safely at an altitude of over 21,000km
The new measurements from JWST have ruled out a collision with the Moon. Instead, asteroid 2024 YR4 will pass over 21,000km above the lunar surface. This is still a close encounter but poses no danger to our planet or its natural satellite. Had it impacted on the near side of the Moon, scientists would have witnessed their first close-up look at a massive impact event and Earthlings would have seen a brilliant flash and new crater about 1km across.