Recently, according to media reports such as Space News and CNN, a small asteroid with temporary designation "2024 YR4" may impact Earth in 2032, triggering close attention from major global space agencies. Where did this asteroid come from? How was it discovered? Do we need to worry about it? On December 27, 2024, a suspicious target flashed through the lens of the Asteroid Impact Warning System (ATLAS) telescope funded by the National Aeronautics and Space Administration (NASA) in Rio Hurtado, Chile. Based on the brightness of reflected sunlight, it was inferred to be an asteroid with a diameter of approximately 40-90 meters. Based on the preliminary orbital data obtained through calculation, the "Sentinel" impact monitoring system operated by NASA's Center for Near Earth Object Research (CNEOS) quickly determined that the asteroid 2024 YR4 is orbiting in an elliptical orbit around the Sun and is likely to collide with Earth on December 22, 2032. However, due to limited initial data and a large range of orbit calculation errors, the predicted probability of impact at this time is very small. As more and more data is collected, the accuracy of orbit calculations is increasing, and the probability of impact is gradually increasing. On January 27th of this year, CNEOS discovered that the probability of 2024 YR4 impacting Earth has exceeded 1%, meeting the notification standards of the International Asteroid Warning Network (IAWN). On January 29th, IAWN announced that 2024 YR4 is listed as a potential impactor and issued an alert to the United Nations Office for Outer Space and the international organization "Space Mission Planning Advisory Group" responsible for coordinating global efforts to avoid asteroid impacts. On February 7th, NASA announced that the probability of a 2024 YR4 impact on Earth has increased to 2.3%. On February 18th, the probability of impact further increased to 3.1%. 2024 YR4 was once considered the 'most dangerous asteroid in 20 years'. Internationally, the "Turin Index" is often used to measure asteroid threats. The Turin Index for 2024 YR4 once reached 3 points, second only to the "Apophis" asteroid, which was rated 4 points in 2004. It currently ranks first on the list of high-risk asteroids tracked by NASA and the European Space Agency (ESA). The power is equivalent to hundreds of nuclear bombs. The Turin index takes into account both impact probability and power, with a score of 3 indicating that the probability of an asteroid colliding with Earth exceeds 1% and may cause local damage. In fact, asteroid collisions with Earth occur almost every day, but the vast majority of "extraterrestrial visitors" burn up in the atmosphere and do not cause any damage. Asteroids of the 2024 YR4 class only collide with Earth once every few thousand years on average. NASA's Sentinel system estimates that 2024 YR4 will weigh approximately 220 million kilograms, impact Earth at a speed of 17.32 kilometers per second, and release approximately 7.7 million tons of TNT equivalent, equivalent to 500 Hiroshima atomic bombs. Space News and other media have referred to 2024 YR4 as a 'city killer'. In February 2013, an asteroid impact occurred in Chelyabinsk, Russia, resulting in nearly 1500 injuries. NASA estimates that the impact energy is approximately 500000 tons of TNT, which is only 1/16 of the estimated 2024 YR4 value. In 1908, a major explosion occurred in the Tunguska region of Russia, destroying 2150 square kilometers of forest and causing the destruction of tens of millions of trees. The cause of this explosion is generally believed to be the impact of an asteroid with a diameter of 50-60 meters, and ESA believes that its destructive power may be similar to that of 2024 YR4. Fortunately, the Tunguska region is vast and sparsely populated, with relatively few casualties caused by the explosion. According to the statement released by IAWN, the potential impact area of 2024 YR4 spans across the Pacific, northern South America, Atlantic, Africa, Arabian Sea, and South Asia regions, with multiple densely populated countries under its potential threat. Therefore, although the 2024 YR4 impact will not cause destruction to the Earth or any other country, it could still be very deadly. Data shows a significant decrease in the probability of impact. David Rankin, an aerospace engineer at the University of Arizona and known as the "asteroid hunter," said in an interview with relevant media that the asteroid is "not worth losing sleep about" and believes that the probability of impact will decrease significantly. Currently, scientists are attempting to obtain more data in order to more accurately assess the risk of a collision between 2024 YR4 and Earth, and to obtain precise information about its shape, material, and other features. Since early January this year, the Magdalena Ridge Observatory in New Mexico, the 1.54-meter telescope in Denmark, the Very Large Telescope in Chile, the Panoramic Survey Telescope at the Hawaii Observatory, and the Rapid Response System have all begun closely tracking 2024 YR4. However, the current asteroid is over 48 million kilometers away from Earth and is currently getting farther and farther away, so these telescopes may only be able to observe it in April. ESA has announced that it will use the James Webb Space Telescope to observe 2024 YR4 in March and May. We will have to wait until the end of 2028 when this asteroid approaches Earth again before we can observe it. Detailed data is important for assessing impact risk. In December 2004, NASA's Sentinel system discovered that the probability of the asteroid Apophis colliding with Earth in 2029 was as high as 2.7%, with a Turin coefficient of 4. But with the acquisition and analysis of more data, just a few days later, the probability of impact was corrected to 0.004%. 2024 YR4 seems to be following the old path of 'Apophis' and may become a' false alarm '. On February 19th, NASA lowered the probability of impact to 1.5% after analyzing the latest observation data. On the 20th, the probability of hitting the Earth further decreased to 0.28%, and the Turin index was adjusted to 1, but the probability of hitting the Moon increased to 1%. Richard Binzel, the creator of the Turin Index, believes that new observational data is likely to lower the Turin Index to 0. In fact, even if this asteroid really hits Earth, humans have the ability to defend against it. In September 2022, NASA successfully deflected the orbit of the larger and heavier asteroid Dimofos through impact. In 2021, a research team from Lawrence Livermore National Laboratory in the United States published a paper stating that nuclear weapons are a powerful means of asteroid defense. Numerical simulations have found that two months before the impact, detonating a nuclear bomb with a yield of one million tons of TNT next to a 100 meter diameter asteroid can shatter the asteroid, resulting in only 0.1% of the mass of the debris that ultimately impacts Earth. As for the impact on the moon, Professor Collins, a planetary science professor at Imperial College London, believes that humans would be very safe on Earth. The material ejected from the impact may fly towards Earth, but it will burn up in the atmosphere. (New Society)