Asteroid 2024 YR4 – Impact Risk Assessment

Asteroid 2024 YR4, a "city killer"-sized space rock (estimated between 40-100 meters wide or 131-295 feet), has briefly become the riskiest asteroid ever recorded due to a non-zero probability of impacting Earth in December 2032. Initial assessments calculated a potential impact probability as high as 3.1%, later revised down to 1.5%. While the initial impact probability was the highest ever seen for an asteroid of this size, scientists emphasize that this is a dynamic situation and the probability is expected to fluctuate and ultimately decrease as more data is collected. The asteroid is currently classified as a 3 on the Torino Scale, indicating a potential for localized destruction and meriting public attention.

Key Themes and Ideas:

• Fluctuating Risk Assessment: The core theme across all sources is the changing nature of the risk assessment for 2024 YR4. As more observational data becomes available, the predicted orbit becomes more precise, leading to shifts in the calculated impact probability. This is a normal process in near-Earth object (NEO) tracking. As Lee Billings states, "Asteroid 2024 YR4’s risk of hitting Earth is shifting with new data, astronomers say".
• Initial High Risk & Subsequent Reduction: The initial assessments in mid-February 2025 showed a relatively high impact probability, triggering concerns. CNN reported on February 19th that "A recently discovered asteroid, named 2024 YR4, is now the riskiest asteroid ever detected". However, later data, especially after the full moon passed, led to a significant reduction in the calculated risk. This highlights the importance of continuous observation. As the editor's note in the Scientific American excerpt points out: "Hours after this story’s publication, NASA announced that new data collected overnight had reduced the Earth-impact probability for asteroid 2024 YR4 from a record-setting 3.1 percent to 1.5 percent."
• The Torino Scale: The asteroid is currently at a 3 on the Torino Scale, which, according to Richard Binzel (the scale's inventor), indicates "current calculations give a 1% or greater chance of collision capable of localized destruction." The scale is intended to communicate the level of concern to both the public and officials.
• Importance of Continued Observation: All sources emphasize the need for ongoing observation and tracking of 2024 YR4 to refine its orbit and reduce uncertainties. The James Webb Space Telescope (JWST) is expected to play a key role in this effort by observing the asteroid in infrared light. "A team of astronomers will use the keen infrared eyes of NASA’s James Webb Space Telescope to further constrain estimates of the asteroid’s size and trajectory in early March".
• Comparison to Apophis: The articles draw parallels between 2024 YR4 and the asteroid Apophis. Apophis initially had a significant (but ultimately incorrect) risk assessment, which was later revised to zero after further observations. This serves as a precedent for the expected trajectory of 2024 YR4's risk assessment.
• Size and Potential Impact: The asteroid is described as a "city killer," which is a relative term. It is significantly smaller than the asteroid that caused the extinction event, and the potential destruction would be localized. If 2024 YR4 were to impact Earth, the result "could resemble a detonating hydrogen bomb, unleashing enough localized devastation to destroy any unlucky metropolis in the way."
• Mitigation Strategies (Premature at This Stage): While potential mitigation strategies like deflection or destruction are mentioned