Asteroid 2024 YR4 will not hit the Moon after all: new Webb observations removed the last major uncertainty
Asteroid 2024 YR4, a space body approximately 53 to 67 meters in diameter that briefly became one of the most closely watched celestial objects in the planetary defense system last year, no longer poses a danger to either Earth or the Moon. The latest observations carried out with the James Webb Space Telescope confirmed that there will be no impact with the Moon on December 22, 2032, although after earlier calculations there was still a small but noticeable possibility of such a scenario.
According to data from NASA and the European Space Agency, the asteroid will pass by the Moon that day at a distance of about 13,200 miles, or just over 21,000 kilometers. This removed the last more serious doubt that remained after the possibility of an impact with Earth had already been ruled out at the beginning of 2025. In practice, this means that 2024 YR4 has now moved from being a scientifically very interesting and media-attractive object for the public into the category of bodies that are still monitored, but no longer carry a concrete impact risk for our planet or its natural satellite.
From the “most dangerous” asteroid to routine monitoring
When 2024 YR4 was discovered on December 27, 2024, as part of the ATLAS system in Chile, automatic early warning systems quickly showed that there was a small probability of its impact with Earth on December 22, 2032. Such early estimates as a rule contain a wide range of possible trajectories because the orbit of a newly discovered object still has to be determined precisely. But in this case the attention was heightened also because of the size of the body: it is an asteroid large enough that, in the event of an impact with Earth, it could cause serious damage on the scale of a city or a wider region.
In the first weeks of tracking, the probability of an impact with Earth gradually increased and at one point reached a level of about three percent, which for an object of that size was enough for 2024 YR4 to briefly become the most striking case in the recent history of monitoring near-Earth objects. NASA later stated that this was the highest recorded impact probability for an object of that size or larger within their modern risk assessments. That is precisely why the asteroid reached the top of European and American risk lists and triggered a coordinated international response within the planetary defense system.
Further observations during January and February 2025 gradually narrowed the uncertainty in the orbit calculation. As early as February 24, 2025, NASA announced that the probability of an impact with Earth in 2032 had fallen to 0.004 percent, with an assessment that the object does not pose a significant threat to Earth even in the foreseeable century. Almost simultaneously, the European Space Agency announced that their Earth risk calculation had fallen to 0.001 percent. This practically closed the Earth scenario, but one other possibility remained: a small part of the possible trajectories still intersected the space through which the Moon was moving at that time.
Why suspicion of a possible impact with the Moon remained
Although the possibility of an impact with Earth was ruled out relatively quickly, the last series of observations left open the question of whether 2024 YR4 could pass so close to the Moon in 2032 that a collision might occur. In spring 2025, experts spoke of a probability of about four percent, and NASA in April of the same year gave an estimate of 3.8 percent, while European sources spoke of approximately four percent. This did not mean that an impact was likely, but that there was still a 96 percent or greater chance that it would not happen. But for science and planetary defense even such a percentage was enough reason to continue monitoring.
The problem was that after spring 2025 the asteroid was becoming dimmer and harder to detect. As it moved farther away from Earth, standard ground-based observations could no longer provide precise enough data to quickly close the case. At that time the prevailing assessment was that new serious observations could be made only in 2028, when its trajectory would once again be favorably positioned relative to Earth. In the meantime, the possibility remained open of using very narrow observing windows with the James Webb telescope, although such an operation was by no means routine.
How James Webb found an almost invisible target
It was precisely the new observations by the James Webb Space Telescope, more specifically its NIRCam camera, that brought the final answer. According to NASA data, the key observations were carried out on February 18 and 26, 2026. This was an extremely demanding task: one of the most complex scientific instruments ever built had to be pointed precisely at an exceptionally faint object, millions of kilometers away, within a very narrow field of view.
Webb was not built primarily for hunting small asteroids. Its main mission is the study of the early universe, distant galaxies, stellar systems, and the atmospheres of exoplanets. Because of this, detecting an object such as 2024 YR4 required very precise planning, almost at the limit of the instrument’s capabilities. Official explanations emphasize that the asteroid was only a “faint dot” against the background of sparsely distributed stars whose positions are very well known thanks to the European Gaia mission. It was precisely this that enabled astronomers, by comparing the asteroid’s position relative to reference stars, to further narrow the uncertainty of its orbit.
ESA’s Near-Earth Object Coordination Centre, NASA’s Center for Near-Earth Object Studies at JPL, and the Webb mission team collaborated in this operation. Such a division of labor shows how today’s planetary defense is not the work of one agency or one country, but of a network of institutions that exchange data, independently verify calculations, and coordinate the publication of results when potentially sensitive risks are involved.
New calculation: the Moon is safe
The result of these observations is now clear. NASA states that the possibility of an impact with the Moon on December 22, 2032, has been eliminated, while ESA’s NEO Coordination Centre, in an announcement dated March 5, 2026, points out that the “threat to the Moon has been removed thanks to JWST observations.” According to NASA’s update, 2024 YR4 will pass by the Moon at a distance of about 21,200 kilometers. In astronomical terms this is a very close flyby, but unquestionably a flyby without impact.
This ended one of the most interesting episodes in the recent tracking of small bodies in the Solar System. At the peak of uncertainty, 2024 YR4 was the subject of daily updates, expert analyses, and public questions about how impact risks are assessed at all. It has now turned out what astronomers had warned from the beginning: initial impact probabilities often sound dramatic, but as new data are collected they most often gradually decrease, sometimes even to zero. This is not a sign that the first estimates were wrong, but that science works exactly as it should — with incomplete data it first defines a range of possibilities, and then narrows it with more precise measurements.
How large the asteroid is and why it mattered
Although it is no longer a threat, 2024 YR4 remains an important scientific object. Based on infrared observations, NASA states that the asteroid has a diameter between 53 and 67 meters, corresponding to the height of roughly a fifteen-story building. Earlier estimates, based on visible light from ground-based telescopes, were broader and less certain. Infrared observations are important because they allow a more precise assessment of size and physical properties, not just the brightness of the object.
Webb observations from March 2025 had already shown that this is one of the smallest objects ever targeted by that telescope and one of the smallest bodies whose size has been estimated more directly by this method. Scientists also obtained additional data on the thermal properties of the surface, that is, on how the asteroid heats up and cools down. According to ESA/Webb materials, the observations indicate that the surface is probably not covered with fine sand, but with coarser rocky material, which is important for understanding the behavior of smaller asteroids and possible future defense strategies.
If, by any chance, a real possibility of an impact with Earth had remained, it is precisely the size, composition, and structure of the object that would have been crucial for assessing the consequences and any possible response. NASA had previously explained that for a body in this size range, the most likely scenario upon entering Earth’s atmosphere would be an airburst, and not necessarily the formation of a large impact crater on the ground. But these are now exclusively theoretical assessments, because the concrete danger to Earth has been ruled out.
The 2024 YR4 case as a test of the planetary defense system
Although the public often associates the term “planetary defense” with film scenarios and spectacular asteroid deflection missions, the 2024 YR4 case showed that the foundation of defense is actually much more down-to-earth and systematic: early detection, rapid orbit calculation, constant data updates, and clear international communication. These are precisely the elements that worked in this case.
As early as February 2025, NASA emphasized that 2024 YR4 provided a valuable opportunity for experts and partner institutions to test in practice the processes of scientific risk assessment and the notification system. In other words, even when an object ultimately does not pose a threat, every such case serves as an exercise for some future scenario in which the warning time might be shorter and the probability of impact greater.
The European Space Agency draws another important lesson from the 2024 YR4 case: the part of the sky from which an asteroid can come from the direction of the Sun is still difficult to monitor with classic telescopes from Earth. That is precisely why ESA is developing the NEOMIR mission, an infrared space telescope planned for the early 2030s, which should observe areas close to the Sun’s glare and detect objects similar to 2024 YR4 earlier. ESA states that, according to simulations, NEOMIR could detect such an asteroid about a month earlier than ground-based systems, which would be valuable for a timely risk assessment.
Why early risk percentages often confuse the public
One of the reasons why cases like this are so media-sensitive is the fact that the public instinctively reads risk percentages differently from astronomers. When an agency announces that there is, for example, a three percent chance of impact in 2032, part of the audience perceives it as a very serious alarm, and another part as proof that it is exaggerated because the probability is small. In reality, both impressions are incomplete.
For scientists, even a small percentage is enough for an object to receive a very high monitoring priority, especially if it is a body capable of causing major regional damage. At the same time, such a percentage does not mean that a catastrophe is likely, but that current observations still do not allow all possible trajectories to be closed down more precisely. At the moment when the orbit is calculated further, the “cloud of possible positions” most often shifts farther away from Earth or the Moon. That is exactly what happened with 2024 YR4 as well. The case therefore shows well why it is important to distinguish the initial danger assessment from the final conclusion.
What comes next
Although the story of a possible impact has ended, monitoring continues. Planetary defense does not stop when one asteroid is removed from the list of immediate threats, but every day tracks thousands of near-Earth objects, assesses their trajectories, and updates risk lists. In March 2026, ESA’s NEOCC still records more than 41 thousand known near-Earth asteroids, while NASA and international partners continue to maintain automatic warning and assessment systems.
In that context, 2024 YR4 will be remembered not as a body that caused a catastrophe, but as an asteroid that showed how far today’s systems have advanced. In just a little over a year, scientists went from the discovery of an unknown object, through a period of heightened caution and increasing impact probability, to almost complete certainty that neither Earth nor the Moon is endangered. There is no spectacular explosion or dramatic interception in space in this story, but there is something more important in the long term: proof that coordinated observation, precise calculation, and international cooperation can answer in time the question that interests the entire planet.
Sources:- NASA Science – official page about asteroid 2024 YR4 with the latest update that the possibility of an impact with the Moon on December 22, 2032, has been removed (link)
- NASA Science – facts about asteroid 2024 YR4, including the estimated size of 53 to 67 meters and confirmation that it will pass by the Moon at a distance of about 13,200 miles (link)
- NASA Science – announcement of February 24, 2025, about the fall of the Earth impact risk to 0.004 percent and the end of the period of heightened warning for Earth (link)
- ESA – official overview of the 2024 YR4 case, including the discovery date, the earlier estimate of approximately four percent for a possible impact with the Moon, and an explanation of the role of the future NEOMIR mission (link)
- ESA NEO Coordination Centre – news of March 5, 2026, that 2024 YR4 will not hit the Moon and that the threat was removed thanks to observations by the James Webb Space Telescope (link)
- ESA/Webb – material on Webb observations from March 2025, describing it as one of the smallest objects Webb has targeted and providing additional data on the thermal properties and size of the asteroid (link)
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