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We know that gas giants around other stars are often located very close to their sun. According to accepted theory, these gaseous planets would have formed very far, then migrated to an orbit closer to the star.
Today, researchers from Lund University and other institutions have used advanced computer simulations to learn about Jupiter's course in our own solar system there are around 4.5 billion years. At that time, Jupiter was formed quite recently, as were the other planets in the solar system. The planets were gradually built by the cosmic dust, which surrounded our young sun in a disk of gas and particles. Jupiter was not bigger than our own planet.
The results show that Jupiter is four times farther away from the sun than its current position suggests.
"This is the first time that we have evidence that Jupiter was formed far from the sun and then migrated to its present orbit, and we found evidence of the migration of Trojan asteroids gravitating around Jupiter," says Simona Pirani. doctoral student astronomy at Lund University and the lead author of the study.
These Trojan asteroids consist of two groups of thousands of asteroids that are at the same distance from the Sun as Jupiter, but gravitate around and behind Jupiter. There are about 50% more Trojans in front of Jupiter than behind. It is this asymmetry that has become the key to understanding Jupiter's migration researchers.
"Asymmetry has always been a mystery in the solar system," says Anders Johansen, professor of astronomy at Lund University.
Indeed, the research community could not explain why the two groups of asteroids do not contain the same number of asteroids. However, Simona Pirani and Anders Johansen, as well as other colleagues, have now identified the reason by recreating the course of events of Jupiter's formation and the way the planet has progressively drawn in its Trojan asteroids .
Through extensive computer simulations, the researchers calculated that the current asymmetry could only have occurred if Jupiter was formed four times further into the solar system and then migrated to its current position. During her journey to the sun, Jupiter's gravity then attracted more Trojans in front of her than behind her.
According to calculations, the migration of Jupiter would have lasted about 700 000 years, about 2 to 3 million years after the beginning of life of the celestial body as an ice asteroid, far from the sun. The inner journey into the solar system followed a spiral path in which Jupiter continued to turn around the sun, but on a narrower path. The reason for the current migration is related to the gravitational forces of the surrounding gases in the solar system.
The simulations show that Trojan asteroids were attracted while Jupiter was a young planet without a gaseous atmosphere, which means that these asteroids probably consist of building blocks similar to those that formed the core of Jupiter. In 2021, NASA's spacecraft Lucy will launch into orbit around six Trojan asteroids of Jupiter for study.
"We can learn a lot about the core and training of Jupiter by studying the Trojan horses," said Anders Johansen.
The authors of the study also suggest that the gas giant Saturn and the ice giants Uranus and Neptune could have migrated in the same way.
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