A fireball that streaked across central Alberta in 2021 was mostly made from rock and not ice, according to researchers from the University of Western Ontario (UWO). The findings challenge long-held beliefs on how the Solar System was created. 

Astronomers tracking the rocky meteoroid concluded that the object came from the Oort Cloud, a collection of icy objects at the edge of our Solar System. However, theories about the formation of the Solar System are built on the assumption that only icy objects exist in the outer reaches of it.

“This discovery supports an entirely different model of the formation of the Solar System, one which backs the idea that significant amounts of rocky material co-exist with icy objects within the Oort cloud,” said Denis Vida, a UWO meteor physics postdoctoral associate, in a statement.

“This result is not explained by the currently favoured Solar System formation models. It’s a complete game changer.”

The meteoroid was tracked over Alberta at 6:23 a.m. on Feb. 22, 2021. It lit up the sky with a bright blue streak as it entered the atmosphere and crashed somewhere near Athabasca, Alberta. The meteoroid is roughly the size of a grapefruit and weighs two kilograms.

Previous rocky meteoroids have come from much closer to Earth. But UWO researchers calculated the object’s trajectory and found it travelled on an orbit usually reserved for icy long-period comets from the Oort Cloud.

Researchers determined the fireball was rocky because it entered the atmosphere at an angle that was much deeper than icy objects on similar orbits. It also broke apart like a rocky meteorite, whereas a comet would have slowly vapourized.

“In 70 years of regular fireball observations, this is one of the most peculiar ever recorded,” said Hadrien Devillepoix, research associate at Australia’s Curtin University and principal investigator of the Global Fireball Observatory, in a statement.

The Oort Cloud is believed to be a spherical shell enveloping the Solar System. Its inner edge is believed to be 2,000 to 5,000 times the distance between the Sun and the Earth. Its outer edge could be between 10,000 to 100,000 times this distance.

The region has never been observed directly because it is so far away, but every object that has come from its direction has been ice. Sometimes, these icy objects are nudged towards the Sun and appear as comets with long tails.

“We want to explain how this rocky meteoroid ended up so far away, because we want to understand our own origins. The better we understand the conditions in which the Solar System was formed, the better we understand what was necessary to spark life,” said Vida.

“We want to paint a picture, as accurately as possible, of these early moments of the Solar System that were so critical for everything that happened after.”The international research team was led by UWO and included researchers from the University of Alberta, Curtin University, Comenius University in Slovakia, NASA Marshall Space Flight Centre, and RASC Calgary Centre. The findings are published in the journal Nature Astronomy.