Asteroid 2024 YR4 triggered the highest impact alert ever recorded for an object of its size. With an initial 3.1% probability of colliding with Earth in 2032, the discovery set off a silent global operation.
Scientists, space agencies, and observatories around the world worked for weeks to pinpoint its orbit, estimate its size, and rule out a threat that kept the astronomical community on edge.
A chance discovery that triggered all the alarms
Everything began on December 27, 2024, when a white dot appeared on the ATLAS system screens in Hawaii. Astronomer Larry Denneau identified the signal and forwarded it to the Minor Planet Center in Massachusetts, as protocol dictates.
Almost simultaneously, the Catalina Sky Survey in Arizona confirmed that the object had passed close to Earth two days earlier. It was provisionally named 2024 YR4, and attention focused on its uncertain trajectory.
NASA, through the CNEOS Sentry system, warned that there was a real possibility of impact. The European Space Agency (ESA) and other institutions confirmed the assessment. It was not a simulation: the threat was real.
The initial size estimate ranged from 20 to 150 meters (66 to 492 feet). This variable was crucial: a small body could disintegrate, but a large one could cause catastrophic damage if it struck solid ground.
International alert and coordinated deployment
On January 29, 2025, the International Asteroid Warning Network (IAWN), backed by the UN, issued a global warning. Earth was facing a possible collision, and planetary monitoring mechanisms were activated.
From NASA, Kelly Fast urgently requested collaboration from observatories worldwide. However, the asteroid was already moving away and conditions for observing it were increasingly adverse.
Possible mitigation missions were even discussed, including the extreme option of using nuclear weapons to deflect its course. Although these were never carried out, the debates exposed the gravity of the situation.
