Unusual properties of Uranus and Neptune, as well as anomalies in the position of dwarf planets, suggest that the solar system "collided" with another star in the first moments of its life. This is the conclusion reached by astronomers who published an article in the Astrophysical Journal.
“The flight of a star through the solar system is a more realistic alternative to the set of hypotheses that now explain the unusual features of our planetary family. In contrast, we have added only one new factor to the classical model of its formation, a second star, and its mechanism of action that leads to the appearance of all known anomalies,”explains Susanne Pfalzner from the Institute of Radio Astronomy in Bonn, Germany.
Four years ago, amateur astronomer Ralph-Dieter Scholz discovered what seemed to him quite an ordinary star - the red dwarf WISE J0720. Now it is in the constellation of the Unicorn, at a distance of about 20 light-years, that is, it is one of the stars closest to Earth.
Two years ago, American astronomers found that Scholz's star relatively recently, about 70 thousand years ago, flew through the solar system. She came to the Sun at a record close distance, about two light years, changing the orbits of many comets and small celestial bodies in the far part of the Oort cloud.
This discovery, as noted by Pfalzner, prompted many planetary scientists to ponder how such convergence between the Sun and other stars could affect the appearance of the solar system. Such meetings, according to a number of researchers, could often occur in the first moments of the life of the star, when it had not yet left the "star nursery", where it was born in the company of dozens of other stars.
For example, the convergence of the Sun and another star may explain why the orbits of Sedna, Biden and many other dwarf planets are unusually elongated and tilted in a special way in relation to the "pancake" of the rest of the solar system. At the same time, they are not far from the Sun at a sufficiently large distance to be recognized as part of the Oort cloud, where such behavior is "permissible" from the point of view of theory.
Pfalzner and her colleagues checked whether this is really so by calculating several dozen variants of a similar "rendezvous" of the Sun and its neighbors. To do this, they created a virtual model of a gas and dust cloud, where the newborn solar system was originally located, and began to push it against luminaries of different masses and sizes.
As these calculations unexpectedly showed, the "collision" of the solar system and another star, whose mass is approximately equal to that of the Sun or was slightly lower than it, explains not only the oddities in the position of the orbits of dwarf planets, but also reveals almost all other mysteries of the "cradle of humanity."
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In particular, the passage of another star at a distance of about 15 billion kilometers from the Sun will cause it to "steal" about two-thirds of the protoplanetary disk. This explains well why the Kuiper belt drops abruptly and becomes noticeably less dense around the same place as Neptune's orbit.
Likewise, this collision explains why Neptune is heavier than Uranus, even though it is further from the Sun and orbits in an unusual orbit. In addition, this idea allows one to resolve another contradiction - how both of these planets were able to form at the distant approaches to the solar system, where the protoplanetary disk was not dense enough for the birth of gas giants.
How likely is such an event? Scientists' calculations show that something similar can happen to any newborn star with a probability of about 20-30 percent in the first few tens of millions of years of its life.
According to Pfalzner, this favorably distinguishes the idea of her team from other hypotheses describing the formation of the solar system, since they include several random factors at once, which can simultaneously occur with significantly lower chances.
