In a rare astronomical event, a diminutive asteroid named 2022 WJ1 was discovered just hours before it exploded in a brilliant green fireball above Niagara Falls on November 19th, 2022. Measuring only about 20 inches in diameter, it's now recognized the smallest space rock ever properly measured, according to a recent study published in The Planetary Science Journal.
The asteroid, roughly the size of an average domestic cat, entered Earth's atmosphere where it disintegrated due to intense friction with the air. The explosion created a spectacular flash of green light that illuminated the skies over Niagara Falls (New York/USA and Ontario/Canada) and was visible to residents in nearby regions New York, Ohio, Pennsylvania, and Maryland. Witnesses reported a loud sonic boom accompanying the event which lasted approximately 10 seconds.
Astronomers from the Catalina Sky Survey in Arizona first detected 2022 WJ1 just three hours prior to its atmospheric entry. Their observation allowed for precise predictions regarding the asteroid's trajectory and enabled monitoring equipment to capture the event in real-time.
Researchers utilized data on the asteroid's brightness collected from both the Lowell Observatory and Western University's camera to conclude that 2022 WJ1 measured between 16 to 24 inches wide. This was a remarkable finding in asteroid research as smaller space rocks often go undetected as they enter Earth's atmosphere until it's too late to measure them.
While larger "potentially hazardous" asteroids are routinely monitored, the detection of smaller asteroids like 2022 WJ1 remains a rare occurrence. This event was only the sixth time astronomers have spotted an asteroid before it impacted Earth.
The ability to detect and analyze such small asteroids is becoming increasingly important as astronomers have recorded a total of 10 early identified impactors, including three in 2024 alone. Notable recent events include an asteroid explosion above Berlin in January and a fireball over the Philippines in September.
Cover photo credit Western Meteor Group
Smallest Asteroid Ever Measured Explodes Over Niagara Falls