On November 18th, 2022, shortly before midnight, the Catalina Sky Survey (CSS) in Arizona and other observatories worldwide detected a small object (now designated 2022 WJ1) heading toward Earth. For the next three hours, the CSS and the Southern Ontario Meteor Network (SOMN) at the University of Western Ontario monitored the object before it entered Earth’s atmosphere above Southern Ontario. At 03:26 a.m. EST (12:26 a.m. PST) on November 19th, the object appeared as a bright fireball that scattered meteorite fragments across the Niagara region.
This event triggered an international collaboration to hunt down the fragments for analysis, but none have been found yet. In a recent study led by Western University and Lowell Observatory, an international team of scientists described a new approach for studying near-Earth asteroids (NEA) based largely on 2022 WJ1. The study is significant in that the team determined the NEA’s composition—the smallest asteroid characterized to date—and established a new and integrated methodology for studying other NEAs that may impact Earth someday.
The study was led by Dr. Theodore Kareta, a Postdoctoral Researcher from the Lowell Observatory. He was joined by researchers from the University of Western Ontario, the ESA’s Planetary Defense Office (PDO), the School of Earth and Planetary Sciences and the International Centre for Radio Astronomy Research (ICRAR) at Curtin University (Australia), the University of Zagreb (Croatia), the Astronomical Society Istra Pula, the Višnjan Science and Education Center, and NASA’s Jet Propulsion Laboratory. The study that describes their technique, “Telescope-to-Fireball Characterization of Earth Impactor 2022 WJ1,” was published on November 22nd in The Planetary Science Journal.
The detection of 2022 WJ1 (WJ1) before it entered the atmosphere was a fortuitous event since it gave astronomers just enough time for scientists to telescopically observe it and gather precise information on its position and motion – which were used to refine its orbit. These factors also allowed astronomers to determine that the asteroid would enter Earth’s atmosphere above the Great Lakes region. The impact location was also fortuitous since it landed in the middle of Western’s network of meteor-observing cameras.
The three hours it took for WJ1 to enter the atmosphere also allowed several members of the Western Meteor Physics Group and Western’s Institute for Earth and Space Exploration (IESE) to watch the object streak through the sky. This was the first time in history that observers were alerted of a natural fireball ahead of time and knew exactly where it would be visible. Paul Wiegert, a professor of physics and astronomy at Western and a study co-author, witnessed the fireball at 3:30 a.m.
“I watched from Brescia Hill on the Western campus,” he said in a recent Western News press release. “Though cold and windy, the hill had a clear view to the east, where I expected to see only a distant flash. Then, the fireball suddenly appeared, passing almost overhead. It was easily visible between broken clouds and noticeably orange-red.” The Lowell Discovery Telescope‘s (LDT) capacity for rapid and stable tracking made it the ideal instrument for observing WJ1, allowing it to keep up with the small and fast-moving NEA.
Teddy Kareta, a postdoctoral associate at Lowell Observatory, observed the asteroid with his team for about one hour before it was lost in the shadow of Earth. As he indicated:
“At the time that we lost the asteroid – when it got too dim to be seen in our images – we had the telescope moving at five degrees per second to try to keep up with it. That’s fast enough that most other telescopes would have had to give up considerably earlier. It’s tremendously fortuitous that this asteroid happened to fly over Arizona’s dark skies at night before burning up over Western’s excellent camera network. It’s hard to imagine better circumstances to do this kind of research.”
By comparing the Arizona-based observations to footage of the meteor acquired by the SOMN, the team determined the size and composition of 2022 WJ1 (WJ1). The size was determined thanks to observations made by the LDT, which detected a silica-rich surface that gave the object a relatively high albedo (reflectivity). By measuring this reflected light, the team calculated the diameter at 40 to 60 cm (16 to 27 inches), making it the smallest asteroid on record.
The combined telescopic and fireball camera data suggest that WJ1 is rich in silica, placing it in the S-chondrite category. They are among the oldest bodies in the Solar System and the most common type of meteorite to hit Earth. “This is only the sixth asteroid discovered before impact,” said Denis Vida, an adjunct professor of physics and astronomy at Western. “Our new approach, discovering an asteroid through space observation and then subsequently observing it with cameras from the ground, allowed us to confirm that our estimates match well to estimates derived using a completely different approach.”
“This is only the second time that an asteroid has been meaningfully characterized with telescopes prior to it impacting the Earth,” said Kareta. “It’s a testament to our good luck and preparation, but it’s also due to the community that cares about keeping the Earth safe from these impactors learning to work together better. This first-ever comparison between telescopic and fireball camera data is extremely exciting and means we’ll be able to characterize the next asteroid to impact the Earth in even better detail.”
While no fragments have been found in the Niagara region, and no further official searches are planned, there are still people in the area who are searching and know what to look for. While much of the fragments were predicted to fall into Lake Ontario, some are hopeful that a fragment or two could turn up in the near future.
Further Reading: Western News