Now the basic theory of the evolution of the Solar system is a model of nice. It is expected that after the dispersion of the original protoplanetary disk four giants - Jupiter, Saturn, Uranus and Neptune turned on nearly circular orbits at a distance of 5.5-17. that is from the Sun, and not in 5-30 as now. Beyond the orbit extreme of these planets were large dense disk of stone and ice planetesimals. And he stretched up to 35. that is from the Sun, beyond the current orbit of Neptune.

Although presumably thrown out of the Solar system's gas giant wandering about, apparently, in interstellar space without the stars, he could be seized one of them and now revolve around other suns. (Illustration : NASA, ESA, G. Bacon.)

On the inner edge of the disk planetesimals periodically gravitational interacted with the remote giant, which would alter their orbits. Planet captured small icy body, drawing them closer to the Sun, while sharing the angular momentum with planetesimals. To offset the transferred moment giant slightly shifted from the Sun, Dating back more often to find the planetesimals and send them to the sun, and so on... So, the orbit of Uranus, Neptune and Saturn consistently moved outward, until planetesimals were not near Jupiter. After a few hundred million years of Jupiter and Saturn, the two inner planets-giant, entered the orbital resonance 1:2 or 2:3), dramatically increasing eccentricity of their orbits, destabilizing the entire system. Under the influence of Jupiter Saturn moved to his current position, simultaneously pushing out from the Sun, Neptune and Uranus.

The model explains well the many details of the history of our planetary system, including the late heavy bombardment. But it has drawbacks. In particular, all attempts to accurately model the above processes end in failure: one of the four giants turns out a tramp; earth-planets start to collide with each other - or worse, the orbit of Jupiter is incorrect, passing destabilizing the orbits of the other phone

Why do we not see anything like this in practice? David Nesvorny from the Southwest research Institute in boulder (USA) and Alessandro Morbidelli from the Observatory of the Cote d'azur (France) tried to solve the problem, assuming that the model is correct, just in its development took part more components than expected.

So, here is what came out. A fifth giant could protect the planet earth from frequent collisions between a (somewhat surprisingly) and simultaneously stabilized the system in the period of migration of the giant planets to the outer orbits. Stabilization has produced a negative impact only on the planet itself - in the end, she was thrown out by the gravity of Jupiter from the Solar system by purchasing a speed higher than a third of the space.

The current state of things was also checked to ensure that the script with the original sixth giant planet. But the probability of evolution of such a system in modern turned out to be somewhat less than five giants, although significantly higher than in fundamentally unable to come to today's picture of the system does not have additional giants.

According to the researchers, on the properties of the planet-exile was something in-between Neptune and Uranus, under similar mass and density. At the same time, if the correct model with six giants, two of which were later expelled, the mass of both the exiles had to be half of the mass of Neptune (8-9 earth)that puts them in a class of supersell". Such an option, by the way, explains to some extent the lack of planets of this kind in the present Solar system - with their very frequently detected at all.

As far as the model of nice with the expulsion of the giant planets may be typical of the Universe? While we could not find a similar system elsewhere. Scheme "earth-the planet - asteroid belt - gas giants - ice giants", but still with a large gap between the planets, is very different from the known about other systems; moreover, already known cases, when the giants are placed closer to the star than earth planet.

After approximately 10 thousand simulations system development astronomers concluded that from its primary condition implies a lot of options with different distribution of orbits of planets, not coinciding with the present. The probability of the formation of the Solar system in its present form is equal to about 5%, i.e. only every twentieth star system will have this rare distribution of planets in the corresponding hierarchy. However, given the current data on the number of planetary systems, this means that only in our Galaxy exceptions must be at least a few billion.

Based on the arXiv.