Continuing the hunt for the mysterious “Planet X”

In January 2016, astronomers Mike Brown and Konstantin Batygin published the first indirect evidence of the existence of another planet inside the solar system. The cosmic body, which received the unofficial name “Ninth Planet”, is yet a hypothetical object whose orbit, 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 the answer to the most important question – where could this Ninth Planet 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 can be an exoplanet drawn to our solar system at some point in its history. However, the latest study by astronomers seriously casts doubt on the latter option and suggests that the Ninth Planet was most likely formed much closer to the Sun than it is now, and then migrated to the outer boundaries of the system with the course of history.

A team of specialists led by Dr. Richard Parker of the Department of Physics and Astronomy of Sheffield University conducted a study together with colleagues from the Swiss Higher Technical School of Zurich. The results of the study of astronomers were published in the journal Monthly Notices of the Royal Astronomical Society (“Monthly notes of the Royal Astronomical Society”).


The six most remote of the known objects in the solar system are located beyond the orbit of Neptune and mysteriously aligned in a single direction. The diagram was created using the WorldWide Telescope program

The question of the existence of the Ninth Planet (or Planet X for those who still consider Pluto a planet) was first raised in 2014 by astronomers Chadwick Trujillo and Scott Sheppard, on the basis of the unusual behavior of certain clusters of extremely remote trans-Neptunian objects (TNOs). From a series of studies conducted in subsequent years, scientists were able to build the basic parameters of an object that could cause such behavior.

At some point, it was concluded that the Ninth Planet may be at least 10 times more massive than the Earth and about two or four times larger than our planet. There is also an opinion that it has a very large elliptical orbit around the Sun with an average distance to the star of about 700 astronomical units (a.e.). In this case, its perihelion (the nearest distance to the star) can be about 200 a. e., and the aphelion (the furthest point of the location of the object from the star) is of the order of 1200 a. Scientists have calculated that in this case the complete revolution around the Sun of the Ninth Planet can take from 10,000 to 20,000 years.

Based on these data, scientists began to doubt that the Ninth Planet could form at its current location. That is why among the astronomers there was a dispute about whether the planet formed closer to the Sun, and then migrated to the outer boundaries of the solar system, or it was attracted by our system from another system several billion years ago.

“We know that the planetary systems began to form simultaneously with the appearance of the first stars. Young stars are very often found in groups where the interaction between stellar objects is a frequent occurrence. The environment where new stars are formed can directly affect planetary systems. Systems can be located very close to each other, so stars of one system can attract stars or planets of other systems, “said Dr. Parker in a press release from Sheffield University.

For the study, a team of astronomers conducted computer simulations of the solar system when it was still in its “child phase,” that is, when the early process of its formation took place. Despite the fact that interaction with other stellar systems (and their planets) during this period of time is considered by scientists to be a frequent phenomenon, the team came to the conclusion that even where all conditions were optimal for catching wandering planets, the probability of capturing the Ninth Planet by our system turned out to be extremely low.

In general, simulations have shown that among objects with such an orbit as the hypothetical Ninth Planet, only 5-10 planets out of 10,000 could be caught and attracted by the Solar System when it was still young. According to the models obtained, the probability that the Ninth Planet was attracted to our system is 1 in 1000 or 2000.

“In this work, we showed that, despite the frequent occurrence of such a capture, it could not possibly have happened with the Ninth Planet. We do not rule out the possibility of the existence of a planet as such, but we believe that it most likely should have formed near the Sun, and not be drawn from another planetary system, “comments Dr. Parker.

If the Ninth Planet was not attracted to our system, then there is only one possibility: it formed inside the system, being closer to the Sun, and then, after a while, moved beyond the orbit of Neptune, settling down where there are some of the most distant objects of the Belt The Kuiper.

The hunt for the “invisible” and mysterious planet continues, any research that adds new data describing its characteristics and nature will be extremely useful in its actual detection. Excluding one for one scenario of its probable formation, scientists also create new questions about the history and evolution of our solar system, requiring the search for answers. How did all the planets of our system appear? They appeared in the same orbits, where they are, or moved there? The closer we get to the Ninth Planet, the more often such questions will arise.