Jupiter’s unknown journey through the early solar system revealed

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It is known that gas giants around other stars are often located very near their sun. According to accepted theory, these gas planets were formed far away and subsequently migrated to an orbit closer to the star. Now, researchers from Lund University and other institutions have used advanced computer simulations to learn more about Jupiter’s journey through our own solar system approximately 4.5 billion years ago. At that time, Jupiter was quite recently formed, as were the other planets in the solar system. The planets were gradually built up by cosmic dust, which circled around our young sun in a disk of gas and particles. Jupiter was no larger than our own planet.

The results show that Jupiter was formed four times further from the sun than its current position would indicate. “This is the first time we have proof that Jupiter was formed a long way from the sun and then migrated to its current orbit. We found evidence of the  in the Trojan asteroids orbiting close to Jupiter,” explains Simona Pirani, doctoral student in astronomy at Lund University, and the lead author of the study.

These Trojan asteroids consist of two groups of thousands of asteroids that reside at the same distance from the Sun as Jupiter, but orbiting in front of and behind Jupiter, respectively. There are approximately 50 per cent more Trojans in front of Jupiter than behind it. It is this asymmetry that became the key to the researchers’ understanding of Jupiter’s migration.

“The asymmetry has always been a mystery in the solar system,” says Anders Johansen, professor of astronomy at Lund University. Indeed, the research community had previously been unable to explain why the two  groups do not contain the same number of asteroids. However, Simona Pirani and Anders Johansen, together with other colleagues, have now identified the reason by recreating the course of events of Jupiter’s formation and how the planet gradually drew in its Trojan asteroids.

Thanks to extensive computer simulations, the researchers have calculated that the current asymmetry could only have occurred if Jupiter was formed four times further out in the solar system and subsequently migrated to its current position. During its journey toward the sun, Jupiter’s own gravity then drew in more Trojans in front of it than behind it.

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