Mystery Fireball That Lit Up Sky and Baffled Scientists Finally Explained

Scientists have found that a mysterious space rock that lit up the skies over parts of Canada in February 2021 wasn't a comet, despite coming from a distant part of the Solar System where comets are thought to originate.

The space rock was spotted in Canada's Alberta province just before dawn on February 22 last year, producing a very bright light and a luminous trail that lasted for several seconds after it plowed through Earth's atmosphere at 38.5 miles per second.

Based on multiple observations, scientists calculated that the object had been on a roughly 1,000-year orbit around the sun before it collided with Earth, meaning it must have come from an extremely distant part of the Solar System known as the Oort Cloud.

This presented a problem. The Oort Cloud is a thick shell of billions or even trillions of icy objects that orbit the sun at distances far beyond the orbit of Pluto. Sometimes some of these objects are knocked out of the Oort Cloud and end up in the inner Solar System, at which point they become comets—giant chunks of ice and dust that develop characteristic trails as they approach the sun.

Map of Canada and Comet
This stock image shows a comet hurtling through space, with an inset of a map of Canada. Scientists recently found that a space rock that lit up the skies over Canada in February 2021 wasn't actually a comet. iStock / Getty Images

Generally, scientists have thought that the Oort Cloud consists of these objects. However, the object that burned up over Alberta didn't look like a comet. Rather, it looked like a meteoroid—lumps of rock or iron that are similar to—but smaller than—asteroids and tend to stay in the inner parts of the solar system.

The existence of rocky meteoroids in the Oort Cloud could change our theories about how the Oort Cloud came to be.

"The Oort Cloud was populated by planetesimals—small objects that accumulated to grow into planets—that were gravitationally scattered by the giant planets, primarily Jupiter and Saturn, as the solar system was forming," Karen Meech, an astronomer at the University of Hawaii Institute for Astronomy, told Newsweek. "Because the giant planets formed in a region of the solar system where it was cold and a lot of icy material was available, it was long thought that the Oort cloud was populated by comets."

Meech and her team have discovered a number of comets from the Oort Cloud that don't behave as they should. For one thing, comets should become active—that is, they should start leaving tails of gas and dust behind them—when they get near the sun. Some of them haven't been doing this, giving them the nickname "Manx comets," with Manx referring to a breed of tailless cat.

One of these Manx comets in particular didn't give off the same color of light as comets tend to. Scientists study the light of comets to work out what they are made out of.

"One of the Manxes so far did not have this type of chemical signature, rather it had an absorption at the far end of the visible spectrum just before the near infrared at 1 micron," Meech said. "This absorption is characteristic of minerals seen in rocky inner solar system asteroids."

Bill Bottke, director of the Department of Space Studies at the Southwest Research Institute, told Newsweek what this means for our theories of how the solar system formed.

"It could tell us that the primordial asteroid belt was more massive, allowing objects ejected from it during early planet formation processes to make up a larger share of the Oort cloud."

The discovery of Oort Cloud non-comets like the Alberta one could also lend support to the Grand Tack hypothesis, which suggests that the planet Jupiter once traveled as close to the sun as Earth in the early days of the Solar System, sweeping up many rocky objects and flinging them out towards the Oort Cloud, Alan Jackson, a planetary astronomer at Arizona State University, Tempe, told the journal Science.

Richard Binzel, professor of planetary science at the Massachusetts Institute of Technology, told Newsweek: "It is naïve to think the Oort Cloud contains only ice. The silicates that make the terrestrial planets would be everywhere in the protoplanetary disk that condensed into our solar system.

"Far from the Sun both ice AND silicates (rocks) can condense. Both ice and rock can survive in the Oort Cloud at cold temperatures for the age of the solar system. Contrast with Earth's distance, ice does not survive and what is left over forms a rocky planet.

"We tend to think that every class of objects fits into their own box. We have to keep in mind that there is likely a continuum of compositions across the solar system. Silicates in the Oort Cloud is no surprise and if an occasional Oort Cloud object is more rocky than icy, so be it."

For now, it is hoped that more unusual fireballs such as the 2021 Alberta event will shed light on such theories.

Research into the 2021 Alberta fireball was presented by Denis Vida, a meteor astronomer at Western University, at the 54th annual Division for Planetary Sciences of the American Astronomical Society meeting held in London, Ontario, between October 2 and October 7 this year.

Update 10/11/22, 7:07 a.m. ET: This article has been updated with a new image.

Update 10/13/22, 8:09 a.m. ET: This article has been updated to include a quote from Richard Binzel, professor of planetary science at the Massachusetts Institute of Technology.