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Oort Cloud news: How many comets from elsewhere?

26 Aug 2021, 12:00 UTC
Oort Cloud news: How many comets from elsewhere?
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Comet Borisov, spotted in 2019, was a visitor from another solar system. It’s the 2nd known interstellar object, and 1st known interstellar comet. But could there be billions more interstellar comets in the Oort Cloud? Image via NASA/ ESA/ D. Jewitt (UCLA).
Oort Cloud news
Astronomers picture the Oort Cloud as a cloud of comets on the farthest outskirts of our solar system. Dutch astronomer Jan Oort theorized its existence in 1950. He said long-period comets are sometimes knocked from their distant orbits in the Oort Cloud (perhaps by passing stars). That’s how they end up in orbits that bring them near our sun. If it exists, Oort thought, this comet cloud is made of material left over from our solar system’s formation 4.5 billion years ago. But is it? Scientists now generally agree that billions of comets must reside in the Oort Cloud. But what fraction of these comets might have originated in other star systems? This week (August 22, 2021), two scientists said the answer might be … most of them.
The two scientists are Amir Siraj and Avi Loeb, both of Harvard. Loeb is also author of Extraterrestrial, the First Sign of Intelligent Life Beyond Earth, ...

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