On Nov. 19, asteroid 2022 WJ1 became one of many small asteroids to hit Earth, but only the sixth we’ve ever seen coming. For the second time this year, humanity has predicted an asteroid impact. The roughly 1m rock caused no damage and burned into the sky above Toronto like a ball of fire. The detection, warning and advance observations of this asteroid illustrate our rapidly increasing ability to warn of asteroid impacts, however small.
The initial discovery of asteroid 2022 WJ1 came from the Catalina Sky Survey – one of the largest projects dedicated to the discovery and follow-up of near-Earth objects (NEOs) – at 04:53 UTC (05:53 CET) on November 19 2022, just under four hours before impact.
The new asteroid was first imaged by Catalina’s 1.5 Mt. Lemmon, and once four observations were made it was reported to the Minor Planet Center (MPC), 38 minutes after the initial detection, at 05:31 UTC.
Those four observations were enough to map the asteroid’s path across the sky, and minutes after this “astrometry” was published, ESA’s internal tracking software reported that the object had about a 20% chance of impact Earth, possibly hitting somewhere in North America in the next two to three hours. Minutes later, other impact monitoring programs also issued alerts outlining a similar scenario.
Following the potential impact notifications, observers at Catalina and elsewhere in the United States have received follow-up observations of the new asteroid. Less than 30 minutes after the initial trigger, the impact was confirmed with excellent accuracy: the small asteroid, probably less than a meter in diameter, would have impacted somewhere between Lake Erie and Lake Ontario, near the US-Canadian border, around 08:00. :27 UTC (09:27 CET).
Exactly at the predicted time, a 1m asteroid impacted the atmosphere becoming a brilliant fireball above the predicted location. Learn more about this event on ESA’s Near-Earth Object Coordination Center (NEOCC) web portal.
Asteroid impact: what is the risk?
Because of how the Solar System was formed, small objects make up the majority in terms of total population. There are an estimated 40-50 million small asteroids and “only” 1,000 of the larger, giant “planet-killing” asteroids. The rest fall somewhere in between.
We currently know of more than 1.1 million asteroids, although many more are out there. Of those discovered, about 30,600 travel in an orbit that approaches Earth’s. These are the “near-Earth asteroids” (NEAs).
The reassuring news is that almost all of the giant asteroids have been found – more than 95% – and none will be of concern for the next hundred years. Astronomers tirelessly search to the last.
Small one-meter asteroids hit the Earth every two weeks. They add to our understanding of asteroid populations, fireballs and their composition, but aren’t a high priority when it comes to planetary defense because they pose no real danger.
The objects we’re most concerned about are those “Goldilocks asteroids” that are big enough to do harm if they hit, and there are enough of them out there that we know they will, at some point. The infamous Chelyabinsk impact in February 2013 and the Tunguska impact in June 1908 fall into this category, and when it comes to discovering these asteroids, there is still a lot of work to be done.
That’s why ESA’s Planetary Defense Office is planning new ground-based telescopes and space missions to improve our asteroid detection capabilities, sending the Hera mission to asteroid Dimorphos hit by NASA’s DART mission to test asteroid deflection, as well as working with the international community to prepare for the scenario where a larger asteroid is discovered on a collision course.