Watch: Smallest Asteroid Ever Spotted Hits Earth Over Canada in Green Fireball

A recent study has revealed that the smallest asteroid ever recorded to hit Earth, and the only one to be accurately measured, was roughly the size of an average cat. This tiny asteroid, named 2022 WJ1, exploded in a spectacular green fireball over Canada in 2022. Remarkably, it was detected just three hours before it entered Earth’s atmosphere.

Published on November 22 in The Planetary Science Journal, the study describes the event that took place on November 19, 2022. The asteroid entered the atmosphere and disintegrated violently due to the extreme friction with the air, creating a brilliant green flash that lasted about 10 seconds. The explosion also produced a loud sonic boom, which was heard across a wide area. The event was reported in southern Ontario but was visible to people as far away as Toronto, and even in parts of New York, Ohio, Pennsylvania, and Maryland.

The Catalina Sky Survey, based in Arizona, detected the asteroid just three hours before it hit Earth. Thanks to the short window of time, the team was able to quickly analyze its trajectory and predict its likely impact location. This also allowed scientists to set up equipment along the asteroid’s predicted path to observe it more closely.

Key tools used in monitoring the asteroid included the Lowell Discovery Telescope (LDT) in Arizona and a network of meteor cameras at Western University in Ontario. These resources helped track the asteroid as it hurtled through the sky. Using data from these instruments, researchers were able to estimate the asteroid’s size, which was found to be between 16 and 24 inches (40 to 60 centimeters) wide—making it the smallest asteroid ever to be confirmed.

While smaller asteroids like 2022 WJ1 strike Earth almost daily, they are typically not observed in advance and therefore cannot be measured. However, the timely detection of 2022 WJ1 provided a rare opportunity to study a space rock before it made impact.

NASA routinely monitors larger, potentially hazardous asteroids, but there are instances where smaller ones are only spotted just before they enter Earth’s atmosphere. In fact, 2022 WJ1 was only the sixth such asteroid to be detected moments before impact.

This year, another asteroid was spotted just before it struck Earth. On October 22, a small asteroid, about three feet in diameter, was detected by NASA’s Center for Near-Earth Object Studies (CNEOS) right before it exploded over the Pacific Ocean, about 1,000 kilometers off the coast of California.