In an international study led by Western University and Lowell Observatory, scientists describe a pioneering, integrative approach for studying near-Earth asteroids based largely on a November 2022 fireball event that dropped meteorites in the Niagara region.
The space scientists determined the composition and size of Asteroid 2022 WJ1 (WJ1) before it fractured upon entering Earth's atmosphere by comparing Arizona-based telescopic observations to video captured by Western's Southern Ontario Meteor Network cameras of the fireball (an unusually bright meteor) on November 19, 2022.
The study, published today in The Planetary Science Journal, is significant not only because it reveals key details about WJ1, the smallest asteroid in space to be characterized to date, but also for establishing the methodology for studying other space objects that impact Earth. This is the first time telescope observation and camera captures have been used to study the same space object.
The size of WJ1 was determined with the 4.3-meter Lowell Discovery Telescope (LDT) in Arizona. Observations from the LDT show the surface of WJ1 was rich in silica, meaning it had a medium-to-high albedo (reflected light). Astronomers use the reflected light to calculate the diameter, which was in the range of 40 to 60 cm (16 to 27 inches), making it the smallest asteroid on record.
A sequence of three images showing 2022 WJ1 streaking through the LMI field of view. Each of the individual streaks are how far WJ1 moved in an individual ten-second-long image. (Teddy Kareta/Lowell Observatory)
Combining two techniques
"This is only the sixth asteroid discovered before impact," said Denis Vida, Western physics and astronomy adjunct professor. "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."
Using Western's meteor camera network, Western space scientists captured the asteroid as it entered the atmosphere above London ending near St. Catharines. Modelling based on Western's fireball observations gives the same initial diameter and composition estimate of the asteroid as was found by LDT. The fireball network and telescopic methods also tightly agree on the determination of WJ1's orbit prior to its arrival on Earth.
View of the fireball from Hume Cronyn Memorial Observatory at Western University.
"This is only the second time that an asteroid has been meaningfully characterized with telescopes prior to it impacting the Earth," said Teddy Kareta, postdoctoral associate, Lowell Observatory. "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."
The telescopic and fireball camera data both suggest WJ1 fits into the S-chondrite category of astronomical objects, which are stony bodies rich in silica (thus the "S" designation). They are among the oldest bodies in the solar system and comprise the most common type of meteorite to hit Earth.
"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," said Kareta.
Likely, not all WJ1's fragments burned up in Earth's atmosphere. While initial meteorite searches and some Niagara region residents have searched for meteorite pieces, none have been found so far. Much of the predicted fall area is underwater in Lake Ontario. For the fall area on land, there are no plans to do any further official searching.
"Two years on, any meteorites that fell on land will have blended in with the landscape," said Phil McCausland, a Western Earth sciences adjunct professor and Meteor Physics Group researcher. "That said, there are people in the area who are searching and know what to look for. We may still get lucky and find a meteorite or two from this fall in the coming months and years."
A fortuitous path
WJ1 was first discovered by the Catalina Sky Survey in Tucson, Arizona in November 2022. Soon after, astronomers predicted the object would impact Earth within three hours. This offered just enough time for scientists to telescopically observe the object while it was still in space. It also gave astronomers time to gather the asteroid's precise position and motion to refine its orbit. Together, those factors allowed for a more accurate determination of where the asteroid would enter Earth's atmosphere - over the Great Lakes, on the border of the United States and Canada. The predicted impact site proved fortuitous, falling right in the middle of Western's network of meteor-observing cameras in the same region.
The few hours of advance warning about the asteroid impact allowed several members of the Western Meteor Physics Group and Western's Institute for Earth and Space Exploration time to drive and find clear weather to watch the incoming object, the first time in history that observers were alerted to see a natural fireball.
Western physics and astronomy professor Paul Wiegert, a co-author on the study, was alerted early enough to see the fireball around 3:30 a.m.
"I watched from Brescia Hill on the Western campus. 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," Wiegert said following the event.
The LDT, stationed near Flagstaff, Ariz., was ideal for telescope viewing. Its capacity for rapid and stable tracking meant it could keep up with small and fast-moving near-Earth asteroids. Kareta, who just happened to be scheduled to observe with the LDT that night, imaged the asteroid with his team for about one hour before it was lost in the shadow of Earth.
"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," said Kareta. "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."
