Star invasion into the solar system, new proof
Stars By Louis Spencer JR | September 6, 2018
The solar system was formed from a protoplanetary disk consisting of gas and dust. Since the cumulative mass of all objects outside Neptune is much less than expected, and the bodies there have mainly inclined, eccentric orbits, it is likely that some process has changed the outer solar system already after its formation.
Suzanne Palatzner of the Institute of Radio Astronomy. Max Planck in Bonn (Germany) and her colleagues calculated that a close flight of a neighboring star could simultaneously lead to the observed low mass density in the outer part of the solar system, and to the eccentric inclined orbits of its bodies. Modeling shows that many objects with such orbits still await their discovery, including the hypothetical Planet 9 or Planet X.
The basic scenario of the formation of the solar system has long been known – the Sun was born from a collapsing cloud of gas and dust. In the process, a flat disk was formed, in which large planets and smaller objects, such as asteroids and dwarf planets, grew. The structure of the disk assumes that the orbits of all bodies will be in the same plane, unless something breaks the idyll. In the solar system, up to the orbit of Neptune, everything seems fine: most planets are moving in rather circular orbits, and their orbital slopes are changing only slightly. But outside Neptune chaos begins. The biggest mystery is the dwarf planet Sedna, which moves along an inclined, highly eccentric orbit and so far from the Sun that the planet could not be the cause of such a trajectory.
Just beyond the orbit of Neptune, there is another strange thing. The total mass of all objects falls sharply by almost three orders of magnitude. This happens approximately at the same distance as chaos begins. Is this coincidence accidental?
The scientists suggested that another star approached the Sun at an early stage of system formation, having stolen most of the material from the outer region of the protoplanetary disc and scattering the remaining center along the inclined orbits. Thousands of computer simulations have shown that the best way to fit the model is a solar mass star or slightly smaller, flying at a distance three times the distance from the Sun to Neptune.
However, it is most surprising that the troubled star not only explains the strange orbits of the objects of the outer solar system, but also resolves several other unexplained features, including the mass ratio of Neptune and Uranus and the existence of two different populations of Kuiper belt objects.
Thus, research shows that much of what we know at the moment can be explained by something relatively simple, for example, the span of a star.
An important issue is the probability of such an event. Usually stars are born in large dense groups. Therefore, in the distant past such spans were quite common. After completing another type of modeling, the team found that the probability of such a meeting during the first billion years of life of the Sun is 20 to 30 percent.
The study is not the final proof that another star violated the originally smooth structure of the outer solar system, but it satisfies many observations. If we consider simplicity as a marker of realism, then the new model is the best explanation of the ones proposed so far.