Why the ‘City-Killer’ Asteroid YR4’s Impact Risk is Rising: What You Need to Know

On December 27, 2024, a small but fast asteroid named 2024 YR4 was discovered near Earth. This asteroid is about 50 meters wide and weighs approximately 200,000 tons. It made its closest approach to Earth two days earlier, on December 25, 2024. Since then, astronomers have tracked it closely, allowing us to gather data about its orbit. YR4 travels around the Sun every four years and can get as far away as 4.18 astronomical units, which is near the outer edge of the asteroid belt. Its next close pass will be on December 17, 2028. Although it won’t hit us then, it could potentially be a risk when it returns on December 22, 2032.

Right now, there’s a chance—about 3.1%—that YR4 might collide with Earth in 2032. However, this doesn’t mean we should panic. Our understanding of its orbit will likely improve with more observations, which should lessen the odds of impact. At this point, the asteroid’s predicted path suggests it will pass Earth at a distance of around 160,000 kilometers, which is less than half the distance to the Moon. But there’s uncertainty in those calculations, with possible variations extending as far as 1.28 million kilometers, still within the space that includes Earth.

You might wonder how scientists calculate these risks. When astronomers first spot an asteroid, they collect various data points to determine its position and motion over time. They use gravitational laws to predict its future paths while considering potential errors in their measurements. The more data points they gather—especially from powerful telescopes—the better they can refine their predictions. However, with YR4 discovered late in December after it had already passed its closest point to the Sun, our understanding of its path is still developing.

Asteroids are categorized based on size and potential risk. For instance, smaller asteroids (under 20 meters) don’t generally pose much threat. In contrast, those between 20 and 100 meters, like YR4, could be classified as “city-killers” due to the damage they might cause upon impact. Even with YR4’s rising concern, it currently ranks just a “3” on the Torino scale, indicating a close encounter that merits attention but isn’t an immediate cause for alarm.

The uncertainty in YR4’s path is still high, primarily due to limited observations since its discovery. Its estimated trajectory has a large margin for error, but as scientists gather more data, they expect to gain a clearer understanding of its future movements. Just as with past asteroids, better measurements will most likely show that YR4 will safely pass by Earth.

Despite the current statistics, it’s important to remember that most asteroids are tracked and studied without danger. The majority of those that have been identified and monitored have either missed Earth or been deemed not a threat. In fact, many previous asteroids, like Apophis, were initially thought to pose risks but were later cleared from danger when more precise measurements were taken.

If there ever were a need to redirect an asteroid like YR4, it would require careful planning. For an effective course correction, scientists would need advanced technology and tools to give them a sufficient lead time, ideally years ahead of a potential impact date. In the event of an impending strike, various strategies could be employed to alter its path, such as launching a spacecraft to collide with it and change its trajectory. The further in advance this is done, the easier it is to ensure the asteroid safely misses Earth.

While the probability of YR4 impacting Earth remains low, the path ahead of us is filled with uncertainty. As we gather more precise data, we’ll have a clearer picture of any potential risks and whether action might be necessary. This highlights the importance of continued astronomical observation for planetary defense.

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