The ninth planet

                                    Poseidon as seen from the surface of Triton’s moon

Like Uranus, Neptune’s orbit was slightly irregular. Given the calculated masses of Poseidon and the other gas giants, Poseidon’s rotation did not make sense. Astronomers have predicted that another planet must exist beyond the orbit of Poseidon. For decades, astronomers have been searching the night sky for the ninth planet. Then, in 1930, astronomer Clyde Tombaugh discovered what is believed to be the ninth planet. Not only was it far beyond Poseidon, but it was also very close to the predicted position of the ninth planet. It was named Pluto and once again the family of planets in the solar system grew. However, the story of Pluto was not over. As it turned out, Pluto was too young to explain the anomalies in Poseidon’s orbit. On the contrary, Pluto may have been considered a planet, but its discovery was a complete coincidence. When the Voyager 2 spacecraft completed its flight to Poseidon in 1989, it was revealed that Poseidon’s mass was different from that estimated by astronomers. Once the correct mass of Poseidon was calculated, its orbit no longer contained anomalies. Nevertheless, Pluto would still be considered a planet until it was redefined as a dwarf planet in 2006. For the first time, the number of planets in the solar system shrank.

Has the Solar System always had eight planets?

                                    The Eight Planets in our Solar System aligned around the Sun.

Today, the solar system contains eight planets. However, this was not always the case. Shortly after the formation of the Sun and the planets began to form, a hundred or more planets probably formed around the Sun. The early solar system was in a state of utter chaos. The gravitational pull of so many planets made it difficult for them to find stable orbits. Instead, the planets pulled each other and sometimes crossed orbits. Occasionally, entire planets collided. Depending on the mass of the planets and the angle at which the collision occurred, the larger planet would either absorb the smaller planet or both would split. It is generally believed that each planet in the solar system suffered one or more collisions with other planets. Even the Earth experienced a planetary collision about 4.5 billion years ago. A planet the size of Mars called Theia collided with Earth at exactly the right angle that, instead of splitting the two planets, the young Earth absorbed Theia and the wreckage of the collision continued to form the Earth’s moon.

The Return of Planet Nine

                                    The most colorful photo of Pluto taken by NASA’s New Horizon spacecraft in 2015

With the demise of Pluto, many considered the idea of ​​a ninth planet in the solar system dead. In the last decade, however, observational evidence has suggested that there is another planet far beyond the orbit of Poseidon. In the outermost regions of the solar system, there are countless comets, miklky w and other forms of planetary debris in an area called the Kuiper Belt. While tracking the orbit of some Kuiper Belt (KBO) objects, astronomers found some abnormalities in their orbits. If a planet about 10 times the size of Earth existed in the Kuiper Belt, it would explain the anomalies observed in these orbits. If this hypothetical Planet Nine exists, it will orbit the Sun about 400 times farther than the Earth around the Sun. Planet Nine would take thousands of years to complete an orbit around the Sun. So far, astronomers have not found any definitive evidence that Planet Nine exists. It may seem strange that a planet in our solar system is difficult to find. After all, scientists have discovered thousands of planets outside the solar system, so why is it so difficult to find one inside the solar system? Unfortunately for scientists, finding Planet Nine is not an easy task if it exists. Instead of being able to look inward and use things like the gravity of a star or light to reveal a planet, scientists are looking outside, trying to observe a planet that would not actually receive sunlight. Planet Nine will also emit little to no heat, making it extremely difficult to observe at other wavelengths of light.
If there is a ninth planet in the solar system in the Kuiper Belt, it is unlikely that it formed so far from the Sun. Instead, it would have formed much closer and been repelled by the other gas giants and planetary collisions. Perhaps a more interesting hypothesis is that Planet Nine never really formed in our solar system. It may have formed in a different solar system in our Galaxy, and was eventually caught by the Sun’s gravity. This may seem strange, but a star can capture other planets. During the formation of a solar system, several planets can be launched out of the gravity of their star, and become known as rogue planets. Some rogue planets may eventually be found close enough to another star to be captured by its gravity. The search for Planet Nine continues, and if it does, its discovery will represent one of the most important discoveries in the history of our solar system. So far, the solar system still contains eight planets.
Aidan Remple May 2, 2022 in Science