A piece of space rock that blazed across the skies of Alberta in 2021 is helping researchers better understand a group of icy objects floating along the outer reaches of the solar system.
The fireball hurtled towards Earth on the morning of February 22, 2021, piercing the darkness with a bright blue flash, a sight 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 traveler.
The grapefruit-sized object, weighing around two kilograms, was not a comet after all – and had made a very long journey to Earth.
Data from images of the fireball, which entered Earth’s atmosphere near Smoky Lake, Alberta, and broke up near Athabasca, 85 kilometers to the northwest, shows it was made of rock, not ice.
“Completely unexpected”
Denis Vida, postdoctoral associate in meteor physics 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 around its edges.
“This fireball was unique,” said Vida, the study’s lead researcher.
“It was extremely fast and it was coming from very far away…And yet the way it entered the solar system showed us that 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 towards Earth at a speed of 62 kilometers per second.
The speed and trajectory of the fall suggest it came from the center of the Oort Cloud, a huge cloud of icy objects that circles 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 what’s closer to Earth in the inner solar system all comes from the asteroid belt, which is full of rocky remnants of the formation of the solar system,” Vida said.
“However, the things that exist in the outer solar system are all icy…and as far as we know of those two populations, rocky and icy didn’t really mix.”
The Oort Cloud is a halo of icy space debris the size of mountains or even larger. Reservoir of comets, it could contain billions or even trillions of objects. Sometimes a passing star pushes a piece of its space junk towards the sun. They appear as long-tailed comets in the night sky.
Because it is so far away, the Oort cloud has never been observed directly. But everything that came out of it was made of ice, not rock. So far.
Vida said there have been suspected cases of meteoroids coming from the Oort Cloud before, but none that could be studied so closely.
“This fireball is the first evidence we have of rocky objects in the outer solar system,” he said. “When it entered the atmosphere, we were able to measure exactly at what pressures it broke up, and there’s no way it was a comet.
“And there’s just no physical process that could create something that big and rocky in the outer solar system.”
Vida describes the rocky Alberta meteoroid as a game-changer. He said our understanding of how the solar system formed is based on the theory that only objects made of ice navigate the Oort Cloud.
“The things we found in the outer solar system had to come from somewhere,” he said.
“We basically knocked out this currently favored model of how the solar system formed and realized that no, the initial asteroid belt had to be too big and there had to be a lot of stuff there.”
The findings suggest that objects from the asteroid belt were scattered throughout the Oort cloud after the solar system formed 4.6 billion years ago, said Chris Herd, a professor in the Department of Science at the Earth and Atmosphere at the University of Alberta.
“[The Oort Cloud] probably started as material in the outer part of the solar system, by the orbit of Neptune, that was scattered, thrown out of that part of the solar system,” said Herd, co-author of the study.
“It’s fine 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 item.”
“Most Particular”
Much of the data for the study came from cameras at the Global Fireball Observatory, developed in Australia and managed by the University of Alberta.
The researchers relied on two high-resolution cameras, one at Lake Miquelon, southeast of Edmonton, and the other near Vermilion, east of the city. The researchers also used doorbell camera footage from a home in Cochrane, northwest of Calgary.
Hadrien Devillepoix, principal investigator of the Global Fireball Observatory, said the fireball underscores the importance of the observatory’s efforts to monitor five million square kilometers of sky.
Catching these “rarer events” is key to understanding our solar system, he said.
“In 70 years of regular fireball sightings, this is one of the strangest fireballs on record,” Devillepoix said in a press release.
The study also involved researchers from the Institute for Earth and Space Exploration at Western University, Curtin University in Australia, Comenius University in Slovakia, Space Flight Center Marshall of NASA and the Royal Astronomical Society of Canada.
Herd said it was exciting to help investigate such a rare meteoroid event. As curator of the university’s meteorite collection, he’s just disappointed the rock didn’t survive his fall.
“We don’t have the rock, which again breaks my heart,” he said. “But at the same time, there’s so much information we’ve learned from the fireball.”
