In January 2016, astronomers Mike Brown and Konstantin Batygin published the first circumstantial evidence for the existence of another planet inside the solar system. The space body, which received the unofficial name "The Ninth Planet", is still a hypothetical object, the orbit of which, according to scientists, lies extremely far from our Sun. Since the publication of Brown and Batygin, other astronomers have conducted more than one study and tried to find an answer to the most important question - where did this Ninth Planet come from?
While some studies suggest that the planet was pushed to the edge of the solar system after its formation, others believe that the object may be an exoplanet pulled toward our solar system at some point in its history. However, the latest research by astronomers casts serious doubt on the latter option and suggests that Planet Nine was most likely formed much closer to the Sun than it is now, and then migrated to the outer boundaries of the system over the course of history.
A team led by Dr. Richard Parker from the Department of Physics and Astronomy at the University of Sheffield conducted the study with colleagues from the Swiss Higher Technical School of Zurich. The results of the astronomers' research have been published in the Monthly Notices of the Royal Astronomical Society ("Monthly Notes of the Royal Astronomical Society").
The six most distant known objects in the solar system lie beyond the orbit of Neptune and are mysteriously aligned in a single direction. Diagram created using WorldWide Telescope software
The question of the existence of Planet Nine (or "Planet X" for those who still consider Pluto a planet) was first posed back in 2014 by astronomers Chadwick Trujillo and Scott Sheppard based on the unusual behavior of certain clusters of extremely distant trans-Neptunian objects (TNOs). From a series of studies in subsequent years, scientists have been able to construct the basic parameters of an object that could cause this behavior.
At some point, it was concluded that Planet Nine could be at least 10 times more massive than Earth and about two to four times larger than our planet. It is also believed that it has a very large elliptical orbit around the Sun with an average distance to the star of about 700 astronomical units (AU). Moreover, its perihelion (the closest distance to the star) can be about 200 AU. e., and the aphelion (the farthest point of the object from the star) is about 1200 AU. e. Scientists have calculated that in this case, a complete revolution around the Sun for the Ninth planet can take from 10,000 to 20,000 years.
Based on this data, scientists doubted that Planet Nine could have formed at its current location. That is why a dispute arose among astronomers about whether the planet formed closer to the Sun, and then migrated to the outer boundaries of the solar system, or whether it was pulled by our system from another system several billion years ago.
“We know that planetary systems began to form at the same time the first stars appeared. Young stars are very often found in groups where interactions between stellar objects are common. The environment where new stars are formed can directly affect planetary systems. Systems can be very close to each other, so the stars of one system can attract stars or planets from other systems,”- said Dr. Parker in a press release from Sheffield University.
Promotional video:
For the study, a team of astronomers conducted computer simulations of the solar system while it was still in its "childhood phase", that is, when the early formation process was taking place. Despite the fact that interaction with other star systems (and their planets) during this time period is considered by scientists to be a frequent phenomenon, the team concluded that even where all conditions were optimal for catching wandering planets, the probability of the capture of the Ninth planet by our system turned out to be extremely low.
In general, simulations have shown that among objects with an orbit like the hypothetical Planet Nine, only 5-10 planets out of 10,000 could have been caught and pulled by the solar system when it was still young. According to the resulting models, the probability that Planet Nine was drawn to our system is 1 in 1000 or 2000.
“In this work, we have shown that, despite the frequent occurrence of such a seizure, a similar one with the Ninth planet, most likely, could not occur. We do not exclude the possibility of the existence of the planet as such, but we believe that it, most likely, should have formed near the Sun, and not be attracted from another planetary system,”comments Dr. Parker.
If the Ninth Planet was not attracted to our system, then there is only one probability: it formed inside the system, being located closer to the Sun, and then, after some time, moved beyond the orbit of Neptune, located where some of the most distant objects of the Belt are located Kuiper.
The hunt for the "invisible" and mysterious planet continues, any research adding new data describing its characteristics and nature will be extremely helpful in actually detecting it. Excluding one by one scenarios of its likely formation, scientists are also posing new questions about the history and evolution of our solar system that require searching for answers. How did all the planets of our system appear? Did they appear in the same orbits where they are, or have they moved there? The closer we get to Planet Nine, the more often such questions will arise.
Nikolay Khizhnyak
