'Unique' Alberta fireball helps astronomers shine new light on origin of solar system
Rocky meteoroid broke up near Athabasca, north of Edmonton, in February 2021
A hunk of space rock that blazed across the Alberta sky in 2021 is helping researchers better understand a cluster of icy objects floating along the farthest reaches of the solar system.
The fireball sped toward Earth on the morning of Feb. 22, 2021, piercing the dark with a flash of bright blue, a spectacle that was visible across the Prairies. Captured on doorbell cameras across the province, the flash lit up social media.
New research from a team of international scientists, published Monday in Nature Astronomy, sheds new light on the space traveller.
The grapefruit-sized object, weighing about two kilograms, was not a comet after all — and had taken a very long journey to Earth.
Data gleaned from footage of the fireball, which entered Earth's atmosphere near Smoky Lake, Alta., and broke up near Athabasca, 85 kilometres to the northwest, shows it was made of rock, not ice.
Denis Vida, a meteor physics postdoctoral associate at the University of Western Ontario, said the object's trajectory challenges a prevailing theory about the formation of the solar system and what is currently floating about on the edges of it.
"This fireball was unique," said Vida, the lead researcher on the study.
"It was extremely fast and it came from very far away … And yet, the way it entered the solar system showed us it was rocky, which was completely unexpected."
Instead of vaporizing like an icy comet, the fireball broke apart and descended much deeper into the atmosphere than icy objects on similar trajectories. It fell toward Earth at a speed of 62 kilometres per second.
The speed and trajectory of the fall suggest it came from the centre of the Oort Cloud, an immense cloud of icy objects that encircles the Sun at an incredible distance from the blazing star.
All previous rocky fireballs have arrived from the asteroid belt, much closer to Earth.
'The rocky and the icy'
"We know from decades of observation that stuff that is closer to Earth in the inner solar system, all of that comes from the asteroid belt, which is full of rocky remnants from the formation of the solar system," Vida said.
"However, the stuff that exists in the outer solar system are all icy … and as far as we knew those two populations, the rocky and the icy didn't really mix."
The Oort Cloud is a halo made up of icy pieces of space debris the size of mountains or even larger. A reservoir of comets, it might contain billions or even trillions of objects. Sometimes, a piece of its space debris will be nudged toward the sun and will appear as a long-tailed comet in the night sky.
Because it is so far away, the Oort Cloud has never been directly observed. But everything coming from it has been made of ice, not rock. Until now.
Vida said there have been previous suspected cases of meteoroids believed to be from the Oort Cloud but but none that could be studied so closely.
"This fireball is the first evidence that we have of rocky objects in the outer solar system," he said. "As it entered the atmosphere, we could measure exactly which pressures at which this broke apart, and there is no way this was a comet.
"And there just isn't a physical process that can make anything that big and rocky in the outer solar system."
Vida describes Alberta's rocky meteoroid as a game-changer. He said our understanding of how the solar system was formed is built on the theory that only objects made of ice are sailing around in the Oort Cloud.
"The stuff that we found in the outer solar system had to come from somewhere," he said.
"We basically eliminated this currently-favoured model of the formation of the solar system and realized, no, the initial asteroid belt had to be big and there had to be a lot of stuff there."
The findings suggest that objects from the asteroid belt were dispersed to the Oort Cloud after the formation of the solar system 4.6 billion years ago, said Chris Herd, a professor in the Earth and Atmospheric Sciences department at the University of Alberta.
"[The Oort Cloud] probably started off as material in the outer part of the solar system, out by the orbit of Neptune, that got scattered out, thrown out of that part of the solar system," said Herd, who co-authored the study.
"That's all well and good if if you just have stuff in the outer part of the solar system that originally formed there.
"You expect it to be icy, but then, you know, here we have this object."
Much of the data for the study came from Global Fireball Observatory cameras, developed in Australia and run by the University of Alberta.
Researchers relied on two high-resolution cameras, one at Miquelon Lake, southeast of Edmonton, and the other near Vermilion, east of the city. Researchers also used footage from a doorbell camera from a home in Cochrane, northwest of Calgary.
Hadrien Devillepoix, the principal investigator for the Global Fireball Observatory, said the fireball highlights the importance of the observatory's efforts to monitor five million square kilometres of skies.
Catching these "rarer events" is essential to understanding our solar system, he said.
"In 70 years of regular fireball observations, this is one of the most peculiar fireballs ever recorded," Devillepoix said in a news release.
The study also involved researchers from Western University's Institute for Earth and Space Exploration, Curtin University in Australia, Comenius University in Slovakia, the NASA Marshall Space Flight Center, and the Royal Astronomical Society of Canada.
Herd said it was exciting to help investigate such a rare meteoroid event. As the curator of the university's meteorite collection, he's just disappointed that the rock did not survive its fall.
"We don't have the rock, which again, it breaks my heart," he said. "But at the same time there's so much information we learned from the fireball."