Scientists suggest passing star rattled Oort Cloud, sending comets storming towards early Earth

Long ago, when humans were only just beginning to emerge, Earth might have been pounded by comets, an event possibly triggered by a passing star. This star was nowhere near our planet, and in fact, brushed past the Oort cloud about 2.5 million years ago. But this event stirred up the Oort Cloud, pushing out comets from this region like bullets, which then rained down on Earth. This has been proposed in a new study that will be published in the Nature journal. Researchers wrote that the nearby star HD7977 skimmed past the solar system right about the time humans were taking their place on Earth. This would have had an effect on the life on our planet. “When a star passes through the outskirts of the Solar system, it can gravitationally kick Oort cloud comets towards Earth and generate a major meteor shower that would significantly affect terrestrial life,” author Avi Loeb wrote.

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What is Oort Cloud?

“Our calculations showed that this star passage likely repopulated the Inner Oort Cloud and potentially triggered a significant comet shower on Earth,” he added. The Oort Cloud is a hypothetical region that is believed to exist at the outskirts of our solar system. It is vast, extending anywhere between 2,000 AU to 100,000 times AU. One AU, or astronomical unit, is equal to the distance between the Earth and the Sun. Dutch astronomer Jan Oort was the first to suggest the existence of the Oort Cloud in 1950 as an explanation for long-period comets. It has never been actually observed because it is too far and dark.

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A star shook up the Oort Cloud comets

The Oort Cloud is also divided into two parts - Outer Oort Cloud (OOC) and Inner Oort Cloud (IOC). Loeb, who co-wrote the paper with Zhuoya Cao and Morgan MacLeod, states that HD7977 had something to do with the changing climate during the Pliocene-Pleistocene transition, when Earth started witnessing glacial-interglacial cycles. “The HD7977’s flyby may have caused an enhanced comet flux during the Pliocene-Pleistocene transition, which could plausibly be related to the environmental changes on Earth during this era,” Loeb wrote.

The team also checked for craters that could be attributed to this comet shower and found some of them definitely had “something to do with the comet shower caused by HD 7977.” Loeb stated that while asteroids are believed to have created these craters, cometary bombardment is a more plausible scenario. He clarified that further geological studies are needed to confirm the potential role of the HD 7977 flyby during the Pliocene–Pleistocene transition.