According to team of scientists at the Carnegie Institution for Science, an additional planet located between Saturn and Uranus got flung out of the solar system while it was still in its infancy.
The theory goes that the Sun was once surrounded by a disk of gas and dust. Through countless collisions, planets started to form, orbiting our star at a relatively short distance.
The more massive planets then kicked off a series of gravitational interactions, causing the planets to reshuffle into their current arrangement.
To get a clearer picture of what that arrangement looked like before these interactions, the team conducted some 6,000 computer simulations.
"We now know that there are thousands of planetary systems in our Milky Way galaxy alone," Carnegie postdoctoral fellow Matt Clement, lead author of a paper about the simulations published in the journal Icarus, said. "But it turns out that the arrangement of planets in our own Solar System is highly unusual, so we are using models to reverse engineer and replicate its formative processes."
"This is a bit like trying to figure out what happened in a car crash after the fact — how fast were the cars going, in what directions, and so on," he added.
They found that the final arrangement of Uranus and Neptune, two icy planets furthest away from the Sun, was determined by both the mass of the Kuiper belt, a region of dwarf planets and planetoids in the far reaches of the solar system, and an "ejected ice giant" that was kicked out when the planetary system was still young.
"This indicates that while our Solar System is a bit of an oddball, it wasn't always the case," Clement explained. "What's more, now that we've established the effectiveness of this model, we can use it to help us look at the formation of the terrestrial planets, including our own, and to perhaps inform our ability to look for similar systems elsewhere that could have the potential to host life."
READ MORE: Where were Jupiter and Saturn born? [Carnegie Institute for Science]
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