The Earth is under constant bombardment from space. Dust, pebbles and chunks of rock fall into our atmosphere daily, sometimes burning spectacularly in a fiery streak across the sky.
These bolides, or fireballs, are usually larger chunks of asteroids or comets that have detached from their original bodies and ended up falling into Earth’s gravitational well.
But scientists have determined that one of these fireballs that exploded over Canada last year is not the usual type of meteor. Based on its trajectory across the sky, a team tracked the object across the Solar System to a starting point in the Oort Cloud, a vast sphere of icy objects far, far beyond the orbit of Pluto.
It’s not extremely unusual for material from the Oort Cloud to be ejected and sent inward towards the Sun. However, this burned up and exploded in a way that he said was made of rock, not the frozen lump of ammonia. methane and water that one might expect from an Oort cloud object.
It’s a finding that suggests our understanding of the Oort cloud could use a small tweaking.
“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 within the Oort cloud,” says physicist Denis Vida of the University of Western Ontario to Canada.
“This result is not explained by the currently preferred models of Solar System formation. It is a complete game changer.”
The visitors to the Oort Cloud that we have identified to date are extremely frosty. They are sometimes known as long-period comets, on orbits around the Sun that take hundreds to tens of millions of years, with random, highly elliptical inclinations.
They are thought to have been ejected from the Oort Cloud between 2,000 and 100,000 astronomical units from the Sun due to gravitational influences and hurled inward on their looping paths.
Since quite a few of these long-period comets have been identified, scientists have a decent idea of what characteristics they (and their orbits) have in common.
This brings us to February 22, 2021, when a fireball raced across the sky about 100 kilometers (62 miles) north of Edmonton, Canada. It has been 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 over 148.5 kilometers, providing scientists with detailed data on the object’s trajectory and disintegration. The fireballs are thought to heat up and explode as atmospheric gases seep into tiny fissures in the rock, pressurizing it from within and causing it to explode.
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The object, found by Vida and his team, was about 10 centimeters (4 inches) in diameter, weighing about 2 kilograms (4.4 pounds). It was thought to have fallen deeper into the atmosphere than any other icy object. In fact, its burning and disintegration was exactly consistent with a rocky fireball.
However, when the researchers used the data to calculate its incoming trajectory, the results they obtained were consistent not with the usual local meteor, but with the orbit of a long-period comet.
“In 70 years of regular fireball observations, this is one of the most unique ever recorded. It validates the strategy of the Global Fireball Observatory established five years ago, which expanded the ‘fishing net’ to 5 million square kilometers of skies , and brought together scientific experts from around the world,” says astronomer Hadrien Devillepoix of Curtin University in Australia.
“Not only does it allow us to find and study precious meteorites, but it’s the only way we have a chance to capture these rarer events that are essential to understanding our Solar System.”
From this single object, the researchers were also able to search the Meteorite Observation and Recovery Project database and published literature for possible origins of the Oort Cloud, and identified two other meteors: one that fell over the Czech Republic in 1997, called Karlštejn fireball, on an orbit similar to Halley’s Comet and the 1979 meteor MORP 441, also with a comet-like trajectory.
This suggests that, rarely, rocky meteors could end up on Earth after a long journey from the Oort Cloud, believed to be the primordial material left over from the formation of the Solar System. Understanding how and why the objects remained rocky, and then ended up here, is the next step.
“We want to explain how this rocky meteoroid got this far 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 trigger life,” says Vita.
“We want to paint as accurate a picture as possible of these early moments in the Solar System that were so critical to everything that came after.”
The research was published in Nature astronomy.