About 50,000 astronomical units from the Sun (each AU being equal to the average distance between Earth and the Sun), is the Oort Cloud, which houses billions of objects. Her formation is still unknown since, so far, only some parts of her history have been studied, and always separately. Now, a team of astronomers from Leiden University has managed to calculate the first 100 million years of the history of this mysterious region of the Solar System.
The Oort cloud was discovered in 1950 by Dutch astronomer Jan Hendrik Oort, who proposed that it could explain the occurrence of comets with elongated orbits. But until then, the process of cloud formation was not clear, because it is formed by different phenomena that can hardly be reproduced by computers, some of which lasted only a few years and occurred over relatively short distances. In parallel, others spanned billions of years at distances comparable to those between stars.
Simon Portegies Zwart, an expert in astronomical simulations and the study’s lead author, says that “if you want to calculate the entire sequence on a computer, you’re going to run aground at some point,” which is why, until now, other simulations have been made only with separate events. So, they decided to work with separate events, but they managed to link each other. By using the result of one calculation as a starting point for the next, the team was able to fully map the formation of the Oort cloud. The simulations showed that, in fact, the cloud comes from what is left of the protoplanetary disk of gases and debris that gave rise to the Solar System, 4.6 billion years ago.
In addition, the simulations provided some interesting details: first, the objects that make up the cloud come from different places — the video above, for example, shows the orbital evolution of an asteroid that, after interacting with the gas giants, goes towards the Oort cloud. Among these places is the closest region of the Solar System, with debris and asteroids expelled by the gas giants in our vicinity, but there is another group of objects coming from stars that were the Sun’s neighbors during its formation. So, the cloud may have captured comets that were originally from these stars. But anyway, it was formed after the Sun left the group of stars in which it was born.
Portegies Zwart, co-author of the study, explains that the calculations showed the dynamics and complexity of the process: “with our new calculations, we show that the cloud was born from a kind of ‘cosmic conspiracy, in which stars, planets and the Milky Way they have their own roles”, and pointed out that the individual processes would hardly explain its formation. He was surprised by the results: “only after the calculations were completed, all the pieces of the puzzle suddenly clicked into place, and everything seemed quite natural and evidently; that is, I think, one of the most beautiful aspects of being a scientist.”
The article with the results of the study was accepted for publication in the journal Astronomy & Astrophysics and can now be accessed in the arXiv online repository, no peer review.
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