A large asteroid named 2024 YR4 has garnered widespread attention this week, with scientists initially raising the possibility of it impacting Earth, before subsequently lowering the probability. The initial predictions caused concern, while the revised data offered some relief. This highlights the dynamic nature of astronomical predictions and the importance of continuous monitoring.
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02-23, 2025The latest assessment indicates that the space rock has a 0.28% chance of hitting Earth in 2032, far lower than the 3.1% predicted earlier this week. However, scientists say it is more likely to hit the Moon, with NASA estimating a 1% probability. These updated figures provide a more accurate assessment of the potential risk posed by the asteroid.
Since 2024 YR4 was first observed through telescopes in the Chilean desert two months ago, dozens of other space rocks have come closer to Earth than the Moon, in what sounds astronomically like "near misses." It is highly probable that other space rocks, albeit much smaller, have impacted us or burned up in the atmosphere without being noticed. These unobserved asteroids, including flybys, close encounters, and direct impacts, constitute another side of the asteroid story.
The vast majority of asteroids are harmless. But some asteroids carry the most valuable clues to unlocking the mysteries of the universe, information we are eager to obtain. First detected last December, 2024 YR4 has the potential to hit Earth on December 22, 2032. Asteroids, sometimes also called minor planets, are rocky remnants left over from the formation of the solar system about 4.6 billion years ago.
Under the gravitational influence of other planets, rocks often travel on orbits that bring them closer to Earth. Professor Mark Boslough of the University of New Mexico explained that for most of human history, it was impossible for us to know how close we were to being hit by a large asteroid. "Before that, we were completely ignorant of them," he said. Now we know that fairly large objects—40 meters in diameter or larger—pass between the Earth and the Moon multiple times per year. This is about the same size as the asteroid that exploded over Siberia in 1908, which caused casualties and flattened more than 200 square miles of buildings.
The most serious "near miss," and the closest comparison to YR4, is an asteroid called Apophis, first discovered in 2004, which is 375 meters in diameter, about the size of a cruise ship. Professor Patrick Michel of the French National Center for Scientific Research (CNRS) tracked Apophis and recalled that it was considered the most dangerous asteroid detected. It wasn't until 2013 that we had enough observational data to know it wouldn't hit Earth.
But he said there was a big difference compared to YR4. "We didn't know what to do. We found something, we determined the impact probability, and then thought, who do we call?" he said. Scientists and governments alike were unsure how to respond. If a large asteroid were to hit a populated area, the consequences could be catastrophic. We're not entirely sure how big YR4 is, but if it's at the upper end of estimates, around 90 meters wide, it's likely to remain largely intact without disintegrating as it enters Earth's atmosphere.
Professor Katherine Kumamoto of Lawrence Livermore National Laboratory explained: "The mass of the surviving asteroid could form a crater. Buildings in nearby areas could be destroyed, and people in the local area (tens of kilometers) could be at risk of serious injury." Some people could die. But planetary defense technology has advanced significantly since the Apophis event. Professor Michel is a member of the International Space Mission Planning Advisory Group. Its representatives advise governments on how to deal with the asteroid threat and conduct direct impact exercises.
If an asteroid is heading towards a town or city, Dr. Boslough likens the response to preparing for a major hurricane, including evacuation and infrastructure protection. The Space Mission Planning Advisory Group will meet again in April to decide how to deal with YR4. By then, most scientists expect the risk to be almost entirely gone, as their calculations of its trajectory will become more precise. As Dr. Kumamoto said, we do have options beyond "bracing for impact." NASA and the ESA have already developed technologies to nudge dangerous asteroids off course. NASA's Double Asteroid Redirection Test (DART) successfully crashed a spacecraft into the asteroid Dimorphos to alter its path.
However, scientists doubt whether this would work for YR4, given the uncertainty about its composition and the short window of time to successfully divert it. So, what about those asteroids that do hit Earth? For scientists, an embarrassing truth is that a direct hit on land far from humans is an ideal scenario for asteroids. This allows them to obtain actual fragments of distant objects within the solar system, as well as insight into Earth's impact history. Nearly 50,000 asteroids have been found in Antarctica. The most famous one, called ALH 84001, is believed to have originated on Mars and contains minerals with important evidence about the planet's history, suggesting it was warm and had water on its surface billions of years ago.
In 2023, scientists discovered an asteroid called 33 Polyhymnia, which may contain an element denser than anything found on Earth. This superheavy element would be entirely new to our planet. 33 Polyhymnia is at least 170 million kilometers away, but this demonstrates the enormous potential of asteroids for our understanding of science. The Barringer Crater in Arizona, USA, was formed by the impact of a meteorite about 50 meters wide 50,000 years ago.
Now that YR4 is more likely to hit the Moon, some scientists are excited about it. The impact could provide them with real-world answers to questions they can only simulate using computers. "Even having a data point from a real case would be very powerful," said Professor Gareth Collins of Imperial College London. "How much material is ejected when an asteroid hits? How fast does it travel? How far can it spread?" he asked. This would help them test their model scenarios of asteroids hitting Earth, thereby helping to make better predictions.
YR4 is a reminder that we live on a planet vulnerable to impacts from rocky objects teeming in the solar system. Scientists caution against complacency, saying that a large asteroid threatening human life on Earth is a matter of when, not if, although most expect this to happen in centuries rather than decades. Meanwhile, our ability to monitor space is constantly improving. Later this year, the largest digital camera ever built will begin operating at the Vera Rubin Observatory in Chile, capable of capturing the night sky in incredible detail. The closer and longer we look, the more likely we are to discover more asteroids spinning close to Earth.
