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\t\t\t\t\t\t27\/06\/2025<\/span> Asteroid 2024 YR4\u00a0made headlines earlier this year when its probability of impacting Earth in 2032 rose as high as 3%. While an\u00a0Earth impact has now been ruled out, the asteroid\u2019s story continues.<\/p>\n The final glimpse of the asteroid as it faded out of view of humankind\u2019s most powerful telescopes left it with a 4% chance of colliding with the Moon on 22 December 2032.<\/p>\n The likelihood of a lunar impact will now remain stable until the asteroid returns to view in mid-2028. In this FAQ, find out why we are left with this lingering uncertainty and how ESA’s future NEOMIR space telescope will help us avoid similar situations in the future.<\/p>\n<\/div>\n Asteroid 2024 YR4\u00a0was discovered on 27 December 2024 at the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in R\u00edo Hurtado, Chile.<\/p>\n Shortly after its discovery, automated asteroid warning systems determined that the object had a small chance of potentially impacting Earth on 22 December 2032.<\/p>\n The asteroid is between 53 and 67 metres in diameter. An asteroid of this size impacts Earth on average only once every few thousand years and would cause severe damage to a city or region.<\/p>\n<\/p><\/div>\n Follow-up observations saw the chance of impact rise to around 3%. As a result, the asteroid shot to the top of\u00a0ESA’s asteroid risk list\u00a0and captured global attention as it became the first asteroid to trigger a coordinated international planetary defence response.<\/p>\n Additional observations made over the next few months, including those made using the\u00a0James Webb Space Telescope, allowed astronomers to more accurately measure the asteroid\u2019s orbit around the Sun.<\/p>\n By March 2025, they had enough information to rule out an Earth impact in 2032.<\/p>\n<\/p><\/div>\n 2024 YR4 was first discovered two days after it had already passed its closest point to Earth. It was not detected sooner because it approached Earth from the day side of the planet, from a region of the sky hidden by the bright light of the Sun.<\/p>\n This region of the sky is hidden from the view of ground-based optical telescopes and is a blind spot for asteroid warning systems.<\/p>\n The significance of this blind spot was made clear on 15 February 2013, when the Chelyabinsk meteor, a 20-metre, 13 000-tonne asteroid, struck the atmosphere over the Ural Mountains in Russia during the middle of the day. The resulting blast damaged thousands of buildings, and roughly 1500 people were injured by shards of glass.<\/p>\n<\/p><\/div>\n ESA\u2019s Near-Earth Object Mission in the InfraRed (NEOMIR) satellite, planned for launch in the early 2030s, will cover this important blind spot.<\/p>\n NEOMIR will be equipped with an infrared telescope and positioned at the first Sun-Earth Lagrange Point. By relying on infrared light, rather than visible light, NEOMIR can spot asteroids in a region of the sky much closer to the Sun. It will repeatedly scan this region for the thermal signatures of asteroids approaching Earth that are at least 20 metres across \u2013 like 2024 YR4 and the Chelyabinsk meteor.<\/p>\n \u201cWe looked into how NEOMIR would have performed in this situation, and the simulations surprised even us,\u201d says Richard Moissl, Head of ESA\u2019s Planetary Defence Office.<\/p>\n \u201cNEOMIR would have detected asteroid 2024 YR4 about a month earlier than ground-based telescopes did. This would have given astronomers more time to study the asteroid\u2019s trajectory and allowed them to much sooner rule out any chance of Earth impact in 2032.\u201d<\/p>\n \u201cAs an infrared telescope, like Webb, NEOMIR would have also immediately given us a much better estimate for the asteroid\u2019s size, which is very important for assessing the significance of the hazard.\u201d<\/p>\n<\/p><\/div>\n By March 2025, astronomers had ruled out an Earth impact in 2032. However, the final observations of the asteroid failed to rule out another intriguing possibility: a lunar impact.<\/p>\n The probability that asteroid 2024 YR4 will strike the Moon on 22 December 2032 is now approximately 4%, and this probability was still slowly rising as the asteroid faded out of view.<\/p>\n However, this means that there is a 96% chance that the asteroid will not impact the Moon.<\/p>\n<\/p><\/div>\n We are left with an interesting situation: there is now a 60 m asteroid with a 4% chance of hitting the Moon in 2032. As the asteroid is now too far away to study any further, this probability will remain unchanged until it returns into view in June 2028.<\/p>\n When it does return into view, new observations will be made and it will not take long for astronomers to confidently determine whether the asteroid will, or much more likely, will not, hit the Moon on 22 December 2032.\u00a0<\/p>\n \u201cA lunar impact remains unlikely, and no one knows what the exact effects would be,\u201d says Richard Moissl.<\/p>\n<\/p><\/div>\n \u201cIt is a very rare event for an asteroid this large to impact the Moon \u2013 and it is rarer still that we know about it in advance.\u00a0The impact would likely be visible from Earth, and so scientists will be very excited by the prospect of observing and analysing it. I am sure that detailed computational simulations will be done over the next few years.\u201d<\/p>\n \u201cIt would certainly leave a new crater on the surface. However, we wouldn\u2019t be able to accurately predict in advance how much material would be thrown into space, or whether any would reach Earth.\u201d<\/p>\n In the coming years, as humankind looks to establish a prolonged presence at the Moon, monitoring space for objects that could strike Earth\u2019s natural satellite will become increasingly important.<\/p>\n Small objects burn up in Earth\u2019s atmosphere as meteors, but the Moon lacks this shield. Objects just tens of centimetres in size could pose a significant hazard to astronauts and lunar infrastructure.<\/p>\n<\/p><\/div>\n The discovery of asteroid 2024 YR4 made it clear that time is of the essence when it comes to asteroid detection. In cases like that of 2024 YR4, the later an asteroid is detected, the less time is available for follow-up observations before it fades from view.<\/p>\n Decision makers need as much information as possible when considering potential mitigation strategies, such as deflection missions or evacuation plans: they do not want to be left with an uncertain but significant chance of Earth impact for multiple years.<\/p>\n By keeping watch for asteroids approaching Earth from the direction of the Sun, ESA\u2019s NEOMIR space telescope will fill an important blind spot in our current asteroid detection systems and significantly improve our preparedness for future hazards similar to 2024 YR4.<\/p>\n Follow the links below to find out more about ESA\u2019s other Planetary Defence activities, such as the Near-Earth Object Coordination Centre (NEOCC); the Flyeye asteroid survey telescopes; the Hera mission, which will turn asteroid deflection into a well understood and repeatable technique for planetary defence; and the Ramses mission to intercept and explore the infamous asteroid Apophis as it safely passes close to Earth in 2029.<\/p>\n ESA’s Planetary Defence Office is part of the Agency’s Space Safety Programme. The Programme works\u00a0to monitor and mitigate hazards in or from space, protecting our Pale Blue Dot, its inhabitants, and the vital infrastructure on Earth and in space on which we have come to depend.<\/p>\n<\/p><\/div>\n
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\n\t\t\t\t\t\t\t\t\t\t0<\/span> likes<\/small><\/span><\/p>\n<\/header>\nWhat is asteroid 2024 YR4?<\/b><\/h3>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nWhy did we not detect 2024 YR4 sooner?<\/h2>\n
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nCould we have detected 2024 YR4 sooner?<\/b><\/h3>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nWill asteroid 2024 YR4 impact the Moon?<\/b><\/h3>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nWhen will we know for sure?<\/b><\/h3>\n
What will happen if the asteroid hits the Moon?<\/b><\/h3>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nWhat else is ESA doing to improve Europe\u2019s planetary defence capabilities?<\/h2>\n