Asteroid 2024 YR4 gained attention after its discovery in late December 2024, when automated systems indicated a small chance of Earth impact in 2032. This probability briefly rose to 3%, prompting a global planetary defence response. However, further observations by early 2025 eliminated the threat to Earth.
Despite this reassurance, the final recorded trajectory of 2024 YR4 left a ling by Erica Marchand
Paris, France (SPX) Jun 30, 2025
Asteroid 2024 YR4 gained attention after its discovery in late December 2024, when automated systems indicated a small chance of Earth impact in 2032. This probability briefly rose to 3%, prompting a global planetary defence response. However, further observations by early 2025 eliminated the threat to Earth.
Despite this reassurance, the final recorded trajectory of 2024 YR4 left a lingering 4% probability of impacting the Moon on 22 December 2032. That estimate is expected to remain unchanged until the asteroid becomes visible again in mid-2028, when astronomers will be able to refine its path.
The 60-metre-wide asteroid was discovered at the ATLAS telescope in Rio Hurtado, Chile, just two days after its closest approach to Earth. It had approached from the Sun-facing side of Earth-a zone currently beyond the reach of ground-based telescopes due to solar glare. This blind spot has previously allowed dangerous objects to go undetected, such as the 2013 Chelyabinsk meteor that injured over 1,500 people.
ESA's forthcoming NEOMIR mission aims to address this gap. Scheduled for launch in the early 2030s, NEOMIR will operate from the Sun-Earth Lagrange Point 1 with an infrared telescope capable of detecting objects larger than 20 metres approaching from the Sun's direction. Simulations suggest NEOMIR could have detected 2024 YR4 about a month earlier than ground-based instruments.
"NEOMIR would have detected asteroid 2024 YR4 about a month earlier than ground-based telescopes did," said Richard Moissl, Head of ESA's Planetary Defence Office. "This would have given astronomers more time to study the asteroid's trajectory and allowed them to much sooner rule out any chance of Earth impact in 2032."
Although Earth is no longer at risk, the possibility of a lunar impact remains a scientific curiosity. A collision with the Moon would likely produce a new crater and be observable from Earth, offering scientists a rare chance to study such an event in real time.
"It is a very rare event for an asteroid this large to impact the Moon - and it is rarer still that we know about it in advance," Moissl explained. "The impact would likely be visible from Earth, and so scientists will be very excited by the prospect of observing and analysing it."
With increasing interest in sustained lunar exploration, ESA emphasizes the need to track even small objects that pose potential threats to future lunar missions. Unlike Earth, the Moon lacks an atmosphere to burn up incoming debris, making even modestly sized impacts a risk for lunar infrastructure and astronauts.
The ESA's broader planetary defence efforts include the Near-Earth Object Coordination Centre (NEOCC), Flyeye survey telescopes, and missions such as Hera and Ramses, all aimed at improving early detection and response strategies.
As ESA continues to strengthen these capabilities, the lessons learned from asteroid 2024 YR4 are helping to shape a more vigilant and prepared planetary defence framework for the future.
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