The National Aeronautics and Space Administration (NASA) announced on the 24th (local time) that "asteroid '2024 YR4' poses no risk of colliding with Earth over the next 100 years." When 2024 YR4 was first discovered, it was assessed to have the highest likelihood of colliding with Earth in 2032 among similarly sized asteroids, but recent precise observations revealed the probability to be 0.0017%, effectively ruling out any collision.
An asteroid is a small celestial body that orbits the Sun in a long elliptical path. Asteroid 2024 YR4 was first discovered on December 27 of last year through the ATLAS telescope in Chile. The diameter of 2024 YR4 is estimated to be between 40 and 90 meters, similar in size to large buildings, and it is estimated that if it were to collide with Earth, it would completely destroy an area with a radius of about 50 kilometers. This is comparable in scale to the 'Tunguska' asteroid impact, which destroyed a forest covering an area of 2,150 square kilometers in Siberia in 1908.
When 2024 YR4 was discovered, there was analysis suggesting a potential collision with Earth on December 22, 2032, which attracted attention from the space science community. NASA's Center for Near Earth Object Studies (CNEOS) announced last month that the collision probability for 2024 YR4 was 1.3%. This probability later rose to 1.7% and then decreased to 1.4%, experiencing fluctuations. Earlier this month, the probability peaked at 3.1% on the 18th (local time). This was the highest value for asteroids of similar or larger size.
However, based on additional observational data, NASA analyzed the trajectory and found that the likelihood of this asteroid colliding with Earth is 0.0017% (1 in 59,000), effectively approaching 0%. This means there is a 99.9983% chance it will safely pass by Earth. NASA noted, "As observational data has accumulated, the accuracy of the trajectory predictions for 2024 YR4 has greatly improved," and confirmed that "the expected position on December 22, 2032, is increasingly moving away from Earth."
The European Space Agency (ESA) similarly assessed the collision probability of 2024 YR4 to be 0.002%, aligning with NASA's analysis. With the reduction in collision probability, the Torino Impact Hazard Scale rating for 2024 YR4 dropped from 10 to 0. The Torino Scale is a tool for classifying the potential collisions between celestial objects and Earth, where a rating of 0 indicates that the collision probability is 0 or extremely low.
This case is reminiscent of the asteroid Apophis, discovered in 2004. When Apophis was first detected, it was estimated to have a 2.7% chance of colliding with Earth in 2029 and was observed to be 350 meters in diameter, receiving a score of 4 on the Torino Scale. However, further observations subsequently confirmed that the collision risk would be low, indicating it would pass safely by Earth.
However, the possibility of asteroid 2024 YR4 colliding with the Moon remains at 1.7%. NASA plans to continue monitoring this possibility. Several observatories supported by NASA's Planetary Defense Coordination Office (PDCO) will continue their observations, and in March of next year, the James Webb Space Telescope will also further measure the size and trajectory of 2024 YR4.
The scientific community considers that while the likelihood of asteroid 2024 YR4 colliding with Earth has been ruled out, it has provided an important research opportunity. This case allowed for testing how effectively the planetary defense system and information-sharing systems operate. NASA stated, "We plan to continue updating data on celestial objects approaching Earth in real-time and prepare for similar threats in the future."
References