This is the same asteroid that was suspected of potentially hitting Earth, but updated observations rule out the risk of hitting Earth, but leave the possibility of hitting the Moon. ESA presents: Innovative telescope that will detect threats even from the most problematic direction – close to the Sun
Asteroid 2024 YR4 is not expected to hit Earth – but there is still a 4% chance of a moon impact. The European Space Agency’s planned NEOMIR space telescope is expected to fill a critical gap in existing detection systems, and improve preparedness for future such events.
The asteroid was first discovered on December 27, 2024, by the ATLAS telescope in Chile, shortly after it passed its closest approach to Earth. The asteroid is estimated to be between 53 and 67 meters in diameter – a size that could cause widespread destruction to an entire city if it were to hit the ground.
An early estimate of the risk of impact with Earth was 3%, placing YR4 at the top of ESA’s threat list and triggering a first-of-its-kind emergency response under the international planetary defense protocols. Later, more precise analyses of its trajectory – including observations from the James Webb Space Telescope – made it possible to completely rule out an impact with Earth.
However, recent calculations have raised a probability of about 4% that the asteroid could hit the moon on December 22, 2032. This figure will remain in place until the celestial body comes within observation range again in mid-2028.
This animation illustrates why asteroid 2024 YR4 was discovered just two days after it passed by Earth in December 2024, and why we will have to wait three years before we can know for sure whether it will hit the Moon on December 22, 2032. Credit: European Space Agency (ESA)
A critical gap in detection systems – and what is expected to change
2024 YR4 was discovered late – two days after its closest approach to Earth – because it entered from a celestial sector near the Sun, a region where the Sun’s rays blind ground-based telescopes and prevent observation. This phenomenon is known as a “blind spot” in the detection of near-Earth asteroids.
A similar event occurred with the Chelyabinsk meteor in 2013, whose sudden impact injured about 1,500 people. In order to reduce such risks, ESA plans to launch the NEOMIR space telescope in the coming years, which will be located at the L1 Lagrange point between the Earth and the Sun.
NEOMIR will operate in the infrared range and will be able to detect heat emitted by asteroids even from celestial segments near the Sun – which allows for early detection of bodies 20 meters or larger in size, such as YR4.
Computer simulations performed by ESA showed that NEOMIR would have detected the asteroid about a month earlier than ground-based telescopes – a crucial period of time for analyzing its trajectory and planning a response if necessary.
Is a moon impact expected?
Although the probability of a lunar impact remains relatively low (4%), it is a rare event – both in terms of its very existence, and because it could occur at a time when we know about it in advance. If an impact does occur, it is likely to be visible from the ground and provide a unique scientific opportunity to study the outcome. However, its precise physical impact – including the extent of material ejected from the Moon into space – cannot be accurately predicted at this stage.
As humanity plans a long-term presence on the lunar surface, the importance of detection and monitoring systems for potential threats increases, especially given the fact that the moon has no atmosphere to deter impacts, even from relatively small bodies.
Towards an advanced planetary defense system
The YR4 incident clearly illustrates the importance of detecting asteroids as early as possible. The shorter the time until a potential event, the more significantly the ability to prepare, conduct follow-up observations, and even plan diversion or evacuation missions is compromised.
ESA's NEOMIR telescope is expected to be a vital component in improving the global capacity to warn, monitor and prepare for hazards from space, and to prevent a situation of persistent uncertainty – as occurred in the case of YR4.
What would happen if the asteroid hit the moon?
"Such a lunar impact is very rare, especially when we know about it in advance," explains Dr. Richard Moissel of ESA. "The impact may leave a new crater visible from Earth, but it is not possible to know in advance how much material will be released into space or whether any of it will reach Earth."
With plans to establish a permanent presence on the Moon, monitoring such threats becomes critical. Unlike Earth, the Moon is not protected by an atmosphere – so impacts from smaller objects could be dangerous to astronauts or infrastructure.
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