A fireball that exploded over Canada has been traced to a very unexpected origin

A fireball that exploded over Canada has been traced to a very unexpected origin

The Earth is constantly bombarded from space. Dust, pebbles and chunks of rock fall into our atmosphere daily, sometimes burning up spectacularly in a fiery trail across the sky.

These bolides, or fireballs, are usually larger chunks of asteroids or comets that broke away from their parent bodies and eventually fell into Earth’s gravity well.

But scientists have established that such a fireball that exploded over Canada last year is not the usual type of meteor. Based on its trajectory in the sky, a team traced the object through the solar system to a starting point in the Oort cloud – a vast sphere of icy objects far beyond the orbit of Pluto.

It is not extremely unusual for material from the Oort cloud to be ejected and sent towards the Sun. However, this one burned and exploded in a way that said it was made of rock, not the lump of frozen ammonia, methane, and water that one would expect from an object in the Oort cloud.

It’s a finding that suggests our understanding of the Oort cloud could use a little adjustment.

“This discovery supports an entirely different model of the formation of the solar system, which supports the idea that significant amounts of rocky material coexist with icy objects in the Oort cloud,” says physicist Denis Vida of the University of Western Ontario in Canada.

“This result is not explained by the currently favored models of solar system formation. This is a complete game-changer.”

The visitors to the Oort Cloud that we have identified so far are extremely icy. They are sometimes known as long-period comets, in orbits around the Sun that take hundreds to tens of millions of years, at random and highly elliptical inclinations.

They are believed to have been expelled from the Oort Cloud between 2,000 and 100,000 astronomical units from the Sun by gravitational influences, and thrown inward on their looping paths.

Because a good number of these long-period comets have been identified, scientists have a good idea of ​​what characteristics they (and their orbits) have in common.

This brings us to February 22, 2021, when a fireball streaked across the sky about 100 kilometers (62 miles) north of Edmonton, Canada. It was observed and recorded by multiple instruments, including satellites and two cameras from the Global Fireball Observatory here on Earth.

For 2.4 seconds, these cameras tracked the meteor for 148.5 kilometers, providing scientists with detailed data on the object’s trajectory and decay. The fireballs are believed to heat up and explode as atmospheric gases seep through tiny cracks in the rock, pressurizing it from within and causing it to explode.

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The object, found by Vida and her team, measured about 10 centimeters (4 inches) in diameter, with a weight of about 2 kilograms (4.4 pounds). It was thought to have fallen deeper into the atmosphere than any icy object has ever been known. In fact, its burn and disintegration matched exactly a rocky fireball.

However, when the researchers used the data to calculate its incoming trajectory, the results they got were consistent not with the usual local meteor, but with the orbit of a long-period comet.

“In 70 years of regular fireball observations, it is one of the most singular ever recorded. It validates the strategy of the Global Fireball Observatory created five years ago, which has expanded the ” fishing net” to 5 million square kilometers of sky, and brought together scientific experts from around the world,” says astronomer Hadrien Devillepoix of Curtin University in Australia.

“This not only allows us to find and study valuable meteorites, but it’s the only way to have a chance of catching those rarer events that are critical to understanding our solar system.”

From this unique object, the researchers were also able to search the Meteorite Observation and Retrieval Project database and published literature for possible origins of the Oort cloud, and identified two other meteors: l one that fell over the Czech Republic in 1997, called Karlštejn’s fireball, in an orbit similar to Halley’s comet, and the 1979 meteor MORP 441, which also had a trajectory similar to that of a comet.

This suggests that, rarely, rocky meteors could end up on Earth after a long journey from the Oort Cloud, believed to be primordial material left over from the formation of the solar system. Understanding how and why the objects stayed rocky and then ended up here is the next step.

“We want to explain how this rocky meteoroid got so far away because we want to understand our own origins. The better we understand the conditions under which the solar system formed, the better we understand what was needed to spark life.” , says Vide.

“We want to paint as accurate a picture as possible of those early moments in the solar system that were so critical to everything that happened after.”

The research has been published in natural astronomy.

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