A fireball that lit up the night sky over downtown Toronto, Ontario, and nearby cities was also a test case for tracking larger near-Earth objects that could cause damage on the ground. 

The asteroid, named 2022 WJ1, was detected by the Catalina Sky Survey in Arizona just before midnight Eastern time on November 18. It was likely a metre wide when it entered the atmosphere.

In the first few minutes of its detection, NASA’s Scout impact hazard assessment system predicted a 25 per cent chance of hitting the Earth’s atmosphere, with possible impacts in the Atlantic Ocean off North America’s coast. The trajectory was refined as more astronomers observed the asteroid. 

A group of amateur astronomers at Farpoint Observatory in Kansas watched the asteroid for more than an hour. Scout updated its projections with their data and calculated a 100 per cent impact probability over southern Ontario at 3:27 a.m. EDT.

With more than two hours remaining before impact, scientists within range of the trajectory were told about the asteroid’s presence. As predicted, a fireball was seen over southern Ontario and impacted the Earth at 3:27 a.m. EDT on November 19. 

“The planetary defence community really demonstrated their skill and readiness with their response to this short-warning event,” said Kelly Fast, Near-Earth Object Observations program manager for NASA’s Planetary Defense Coordination Office, in a statement. “

“Such harmless impacts become spontaneous real-world exercises and give us confidence that NASA’s planetary defence systems are capable of informing the response to the potential for a serious impact by a larger object.”

This is the sixth time that astronomers detected an asteroid that was about to hit Earth, and the first time an event was tracked over a major population centre. Astronomers tracking the asteroid say most debris likely ended up in Lake Ontario, but some debris impacted the Niagara region — likely near the town of Grimsby, Ontario. 

The next step is recovering the debris.

“What we need now to complete this story is to recover some of these rocks and find out what kind of material made up asteroid 2022 WJ1,” said Peter Brown, Canada Research Chair in Planetary Small Bodies at Western University, in a statement. “This is very much like a sample return space mission, but in this case the sample fell on us.”