The 'City-Killer' asteroid that triggered a global planetary defense alert
In short: In late 2024, a robotic telescope in Chile detected an object with the highest recorded probability of hitting Earth. While it was initially dubbed a 'City-Killer,' new data from the James Webb Space Telescope has shifted the threat from our planet to its closest neighbor: the Moon.
Discovered on December 27, 2024, by the ATLAS telescope in Chile, asteroid 2024 YR4 quickly became a global priority. Initial calculations suggested it posed a serious risk of colliding with Earth as early as 2032. With an estimated diameter between 53 and 67 meters—roughly the height of a 15-story building—researchers from the University of Western Ontario warned that an impact could be comparable to one of the most powerful thermonuclear bombs in existence, capable of wiping out a megalopolis.
The asteroid's trajectory was so uncertain early on that it triggered the first coordinated international planetary defense response. However, as astronomers gathered more data, the risk profile shifted. By March 2025, refined calculations ruled out an Earth impact but revealed a lingering danger: a chance of striking the Moon on December 22, 2032. This event would be the most powerful lunar impact in 5,000 years and could still result in catastrophic consequences for Earth.
The latest update comes from NASA’s Jet Propulsion Laboratory, which used the James Webb Space Telescope to capture some of the faintest asteroid observations ever recorded. By refining the trajectory, these latest figures exclude a collision with the Moon and estimate the body will clear it by 13,200 miles (21,200 km). Such developments underscore how planetary protection evolves: enhanced accuracy frequently turns 'definite' hazards into 'close calls,' yet they persist as crucial examples for tracking orbits later.
Because 2024 YR4 was only detected two days after its closest approach to Earth, it serves as a stark reminder of the limitations of current surveillance. To prevent similar surprises, agencies like ESA are planning new tools like the NEOMIR space telescope to provide earlier warnings for objects that could otherwise remain hidden until they become critical threats.
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Sources
- Summary by Intellect · source: This Asteroid Has the Highest Impact Probability in History — And It’s Coming Back in 2032
- Also: New NASA Asteroid Observations Eliminate Chance of 2032 Lunar Impact - NASA Science
- Also: Will asteroid 2024 YR4 hit the Moon?
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