Planet 9: The Mysterious "Hidden World" That Baffles Scientists

Several scientists have proclaimed the existence of a world that has not yet been seen by any terrestrial telescope.

Two astronomers published a study in which they postulated the existence of a huge icy planet in the confines of the Solar System, known as Planet 9 POT

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune are the eight planets orbiting the sun . However, for some years the scientific community has recognized the possible existence of a ninth planet in our Solar System .


On January 20, 2016, two astronomers from the California Institute of Technology (Caltech) published a study in which they postulated the existence of a huge icy planet at the edge of the Solar System . The existence of this hidden world, which has since become known as Planet 9 , was deduced from the strange movements of a group of dwarf planets.

The orbits of six of the most distant objects in the Kuiper belt suggest the presence of Planet 9 whose gravitational effect would explain its unusual orbits.
The orbits of six of the most distant objects in the Kuiper belt suggest the presence of Planet 9 whose gravitational effect would explain its unusual orbits.Caltech

Michael Brown and Konstantin Batygin announced the results of the research in the prestigious scientific journal The Astronomical Journal . There they presented the study that led them to conclude the presence of the hypothetical "Planet 9" far beyond Pluto and the Kuiper belt , the distant site that contains hundreds of thousands of objects larger than 100 kilometers and up to a billion kites.

The main problem with the claim made by Brown and Batygin is that no telescope has yet been able to capture the mysterious Planet 9 . So how can the two astronomers be so sure of their existence in the outer Solar System?

The presence of this hidden world at the limits of the Solar System can be argued by the behavior of a group of trans-Neptunian objects . According to the study by Brown and Batygin, the mysterious Planet 9 could be the fifth gas giant , which would have been expelled from the inner Solar System. And its existence, confirmed by mathematical calculations, would explain the peculiar orbits of various dwarf planets beyond Neptune.

The details of the investigation

To explain the study published by Brown and Batygin it is necessary to go back to the year 1992, when two astronomers who had studied the sky for years looking for faint objects located after Neptune, discovered the Kuiper belt , home of the "waste" resulting from the moment in which the Solar System was formed.

The objects within the Kuiper belt are collectively called trans-Neptunian objects and Pluto is its largest and most massive member . But in 2016, Pluto, which was considered a planet, was reclassified as a dwarf planet . Brown himself was one of those responsible for his degradation in cosmic status and has since been known as " the man who killed Pluto ."

Comparison of sizes between objects in the Kuiper belt (Pluto, Sedna and Quaoar) with the Earth and the Moon
Comparison of sizes between objects in the Kuiper belt (Pluto, Sedna and Quaoar) with the Earth and the Moon

Other dwarf planets within the Kuiper belt are: Sedna -which is 40% the size of Pluto-; Quaoar - about half the size - and Eris - almost the same size.

The discovery of these trans-Neptunian objects laid out a fundamental clue in the search for Planet 9 because Sedna was not moving in the logical way that astronomers expected it to, that is, by tracing ellipses around the Sun from within the belt of Kuiper.

In contrast, Sedna travels an unexpected route by swinging a pendulum at a distance 75 times greater than that separating the Earth from the Sun. The orbit of this dwarf planet is so wandering that it takes about 11,000 years to complete the circle. King Star. Thus, the astronomers concluded that "something" was pulling Sedna and dragging it away .

The theory proposed in 2016 by Brown and Batygin of the existence of a huge planet, between five and ten times the size of the Earth, arose from the realization that Sedna was not the only object that was out of place, since there were six other dwarf planets that were dragged in the same direction , a situation so unlikely that it can only be explained by the presence of a star like Planet 9.


A more detailed analysis of the data showed that the six trans-Neptunian objects (Sedna, 2012 VP, 2007 TG, 2004 VN, 2013 RF, and 2010 GB) trace elliptical orbits that are aligned almost in the same direction in physical space and in the same plane. According to the estimates made by Brown and Batygin, this would only happen by chance with a probability of 0.007% .

Thus, the two astronomers suggested the hypothesis that Planet 9 had left a ghostly imprint on the confines of the outer Solar System, distorting the orbits of objects around it with its gravitational pull . Currently, the number of trans-Neptunian objects showing this eccentric orbital pattern and inclination has increased to 19 in total.

Although no one has yet been able to observe the hypothetical hidden planet from a terrestrial telescope , much can be deduced from it. The orbit of Planet 9 is so eccentric that its most distant point is believed to be twice as far as its closest and has an orbital period of between 10,000 and 20,000 Earth years .

According to the calculations of Brown and Batygin, the orbit of Planet 9 would have a semi-major axis of approximately 700 AU, about twenty times the distance of Neptune to the Sun, although it could approach up to 200 AU (30 billion kilometers). The high eccentricity of the ice giant's orbit could take it as far as 1200 AU away from the Sun at its aphelion. The astronomical unit (abbreviated AU) is a unit of length equal to the average distance between Earth and the sun . Thus, taking this measurement into account, the distance that separates a planet from the center of the solar system can be calculated.

The researchers also conjectured what Planet 9 might look like and concluded that it is an icy body with a solid core, such as Uranus or Neptune , that is two to four times the diameter of Earth.

How would Planet 9 have been formed?

There are three main theories about the formation of this mysterious celestial body. The first establishes that the planet was formed in the same place where it is now hiding . Batygin considered this hypothesis relatively unlikely because it would require the Solar System to have stretched as much as its distant refuge.

The second theory is more intriguing and states that Planet 9 is actually an alien impostor , an object stolen from another star long ago when the Sun was still in the stellar group in which it was born. Batygin was also reluctant to this assumption because "the problem with this story is that there is an equal chance that the planet would have been lost in the next encounter."

Orbital correlations between the eight planets that orbit the Sun
Orbital correlations between the eight planets that orbit the SunCaltech

And the third, Batygin's preferred theory, which proposes that Planet 9 would have formed much closer to the Sun , at an early stage in the development of the Solar System, when the planets were beginning to position themselves out of the surrounding gas and dust. And somehow it was around the region of its formation before being scattered by Jupiter or Saturn , and subsequently had its orbit modified by passing stars.

Why didn't anyone see Planet 9?

Astronomers do not look for a certain type of object in a particular place in the cosmos but rather survey a space wide enough to have any chance of finding something . Therefore, hunting a stellar object like Planet 9 is a very complicated exercise because only a tiny portion of the Solar System can host it.

Another factor that is more pragmatic is in the challenge of reserving the right telescope at the right time. "Right now, the only option available to find Planet 9 is the Subaru telescope ," Batygin said. This gigantic instrument has an 8.2-meter mirror and is located atop a dormant volcano on Hawaii's Maunakea .

The Subaru telescope is capable of capturing the weakest light from remote celestial bodies and, for that reason, is the right tool for the search for Planet 9
The Subaru telescope is capable of capturing the weakest light from remote celestial bodies and, for that reason, is the right tool for the search for Planet 9Subaru

The Subaru telescope is capable of capturing the weakest light from remote celestial bodies, and for that reason, it is the right tool for the search for Planet 9 because it would be so far from the Sun that it is unlikely to reflect much of its glare.

"There's only one machine that works for us, and we have it maybe three nights a year, " Batygin lamented. "The good news is that the Vera Rubin telescope is going to be usable in less than two years and they will probably find it," he said.

The Vera Rubin telescope is of the latest generation and is under construction in the north of Chile . It will have an 8.4 meter primary mirror that will be able to photograph the entire available sky every few nights due to its wide field of view. It is expected to be completed and operational by 2022 . Its name comes from the American astronomer Vera Rubin, who was a pioneer in measuring the rotation of stars within a galaxy.

What if it never appears?

There is a scenario that would be irritating for the entire scientific community but that is possible that it happens: that Planet 9 never appears . Because according to a group of astronomers, it could not be a planet but a black hole .

"All the evidence that there is an object there is gravitational," said James Unwin , professor of Physics at the University of Illinois at Chicago , who was the first researcher to defend the idea of ​​the black hole together with Jakub Scholtz , a physicist from the University of Turin in Italy .

The Vera Rubin telescope, which is under construction in Chile, has an 8.4 meter mirror
The Vera Rubin telescope, which is under construction in Chile, has an 8.4 meter mirrorHoward Lester

Black holes tend to include stellar black holes , which have a mass that is at least three times that of the Sun, and supermassive black holes , which are millions or billions of times the mass of the Sun. Born from dying stars, the latter are more mysterious and possibly emerged as colossal stars that imploded, devouring everything around them, including other black holes.

And there is a third type that are the primordial black holes , very different from the previous two. They have never been observed, but are believed to have originated in a hot cloud of matter and energy that formed in the first second of the Big Bang . In this unstable environment, parts of the universe could have become so dense that they were compressed into tiny pockets alongside the mass of the planets.

Unwin and Scholtz argued that the hypothetical Planet 9 could be a primordial black hole , since it is believed that these are significantly smaller.  As these black holes were born in the early phases of the universe, the dense regions they form could have been especially small. Consequently, the mass contained in this black hole can be much smaller than a star and can even be the size of a stone, "said Scholtz. This assumption could fit with the estimate of the mass that Planet 9 is expected to have and which, according to astronomers, could be 10 times that of Earth.


Although Batygin acknowledged the skeptics' point of view, he ruled out the possibility that Planet 9 is actually a black hole . “It is an original idea and we cannot rule out any composition even for its smallest fraction. It may be my own planetary astronomy teacher bias, but planets are a little more frequent, "he said.

And to end the suspicions, he was forceful in defending his theory. “If you decided to eliminate our interpretation and imagine that Planet 9 does not exist, then more problems would be generated than would be solved . Suddenly, we would have many different puzzles and there would be no rational explanation to demonstrate the peculiar behavior of the orbits of dwarf planets, "he concluded.

If in the near future, scientists manage to find the legendary hidden planet, they will have helped to change the knowledge established by science of what happens in our Solar System, and they will have opened a window towards the new discoveries that await us in other remote places. of the galaxy .


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