Wandering world?

In order to explain the early history of the Solar System as a whole, astronomers have proposed several theories in which Jupiter formed at a different distance from the Sun and migrated to its current position, perhaps over a million years or less. The most widely accepted of these is called the Nice model. According to this hypothesis, Jupiter and the other giant planets formed much further out in the Solar System than their current positions, initially arranged in quite close-packed orbits around the current location of Neptune. As Jupiter ploughed through clouds of ice-rich debris that then occupied much of the outer Solar System, an exchange of momentum catapulted these smaller worlds to the very edge of the Solar System – where they now form the distant Oort Cloud of dormant comets – while sending Jupiter and the other planets spiralling in towards the Sun. The process only came to a halt when the region around the planets was largely ‘cleared out’.

1 Young orbits

After the dissipation of the Solar System’s primordial disc, Jupiter, Saturn, Uranus and Neptune could be found on a nearly circular orbit somewhere between 5.5 and 17 astronomical units.

2 Complete chaos

After a slow migration, Jupiter and Saturn caused a regular and periodic gravitational influence on each other, causing eccentric orbits that destabilised the entire Solar System.

3 A shower of planetesimals

Neptune and Uranus scattered rocks from their orbits to the outer reaches, removing nearly all the primordial disc’s mass that once battered the inner planets.