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Imagine the ninth planet. Source: wikipedia humans have observed billions of stars in the Milky way, galaxies tens of billions of light-years away, and even know about the birth of the entire universe. The solar system can no longer hold the imagination of science fiction writers, and many science fiction works regard constant star travel as a common occurrence. But the reality is that even the basic question of "how many planets in the solar system" is still uncertain.

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When the New Horizons (New Horizons) probe flew by Pluto on July 14, 2015, it must recall the afternoon when the International Astronomical Union (IAU) stripped the celestial planet of its title nine years ago. On September 13, 2006, IAU decided to classify Pluto as a dwarf planet (dwarf planet). Just over a year after New Horizons took off, Alan Stern, the project manager, expressed dissatisfaction with the decision: "it was a bad decision... I can only laugh at it." (although it was he who coined the term "dwarf planet" in 1991)

New Horizons shot Pluto. Photo Source: how many planets are there in the NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute / Alex Parker solar system? Since then, the standard answer to this question has changed from 9 to 8. But are there really only eight planets in the solar system? In fact, astronomers have no definite answer to this question.

The rebirth of Planet X in 1930, American astronomer Claire Clyde Tombaugh confirmed the existence of Pluto. The reason for saying "confirmation" rather than "discovery" is that astronomers inferred that there must be a "Planet X" (Planet X) outside Neptune, which affected the orbit of Neptune, based on the abnormal orbit of Neptune. Pluto appeared there when Tombaugh pointed the telescope in the predicted direction. Since then, the number of planets in the solar system has risen from 8 to 9 mi-until it fell back to 8 in 2006.

There are many reasons why Pluto is humiliated. The main reason is that there are too many celestial bodies like Pluto. The average distance between Pluto's orbit and the sun is longer than the semi-major axis of Neptune's orbit (30.1 times the Earth-Sun distance, also known as 30.1 astronomical units, 30.1AU). Astronomers call these objects Neptune extraterrestrial objects (trans-Neptunian object,TNO). In 2005, astronomers discovered a TNO-- star about the size of Pluto. If Pluto is the ninth planet, writers will soon be able to sort out the tenth, eleventh and twelfth planets. As a result, astronomers set a new planetary standard in 2006, classifying Pluto as a dwarf planet. That year, plutoed (Pluto for Pluto) was also named word of the year by the American dialect Society, meaning "downgraded."

Hercules was captured by the Hubble Space Telescope. Photo: NASA, ESA, and M. Brown, however, this is not the first time Pluto has been "disappointed". There is actually a loophole in the discovery of Pluto described above-Pluto's mass is much smaller than the predicted Planet X and cannot have a significant impact on Neptune's orbit at all. The more deadly bug is that Planet X doesn't really exist. In 1989, Voyager 2 flew over Neptune, and a few years later astronomers corrected Neptune's mass according to Voyager's orbit. It was found that Neptune's actual mass should be 0.5% lower than previously predicted-which directly led to Neptune's orbital anomaly "disappearing", and there was no need for Planet X to exist. Tombaugh's discovery of Pluto in that region of the sky was not an astronomical collection of "magical power" based on Newtonian gravity, but a simple coincidence.

Although Pluto is no longer a planet, and Planet X predicted by Neptune's orbit is not necessary, it does not mean that the concept of Planet X has disappeared. In 2014, American astronomers Chadwick A. Trujillo and Scott S. Sheppard published a paper in the journal Nature. They found some similarities in the orbits of several TNO-simply put, the orbits of these TNO are ellipses and their orientations are similar. But if there is a planet X that we haven't observed yet, it could explain the elliptical orbits of these TNO. In 2016, a paper published in the The Astronomical Journal analyzed the orbits of six Kuiper Belt objects (KBO) and found that their orbits were very similar. The probability that this phenomenon happened accidentally was only 0.007%. To explain this small possibility, it may be possible to introduce a more distant planet, XLY-or the ninth planet.

Note that this is a moving picture. Image source: Caltech for this new planet X, astronomers predict that the mass is about 10 times that of Earth, the perihelion is about 200AU, the aphelion is about 1200AU, the semi-major axis is about 400 to 1500 AU, and the cycle around the sun is about 15, 000 years. By contrast, Neptune has an operating cycle of only 165 years.

The sky-high Planet X humans have observed billions of stars in the Milky way, galaxies tens of billions of light-years away, and even know the general birth of the universe. The solar system can no longer hold the imagination of science fiction writers, and many science fiction works regard constant star travel as a common occurrence. But the reality is that even the basic question of "how many planets in the solar system" is still uncertain.

The planet itself does not glow, while Planet X is too far from the sun and the reflection is weak. Without light, man would not have been able to observe the planet. Of course, we can still find it through the thermal radiation of the planet, but telescopes large enough to capture this faint infrared light are often designed for deep space exploration with a very small field of view. using them to find Planet X is like looking for a needle in a haystack-or a very expensive needle in a haystack, because the machine time of these telescopes is very valuable.

So, we don't know yet whether Planet X exists. Since we don't know what it is, we can't stop astronomers from putting forward all kinds of wild conjectures. And Planet X is really worth astronomers' imagination, because in the current theory of planet formation, this distant planet X should not exist at all. The formation of planets requires raw materials, which come from the accretion disk left when the sun was born. But in the current theory, where Planet X is located, there should not be enough raw material to form it.

A natural idea is that Planet X is a "stray planet" captured by the solar system. But compared with the "outrageous" conjecture put forward by astronomers later, this idea is still too conventional.

In 2019, a paper published in the physical Review KuaiBao (Physics Review Letters) suggested that we didn't find Planet X, perhaps not because we didn't have the ability to observe, but because we were looking in the wrong direction. The ninth planet may not be a planet at all, it may be a black hole.

You may wonder-shouldn't black holes have a lot of mass? If there is a black hole in the solar system, why does the earth revolve around the sun instead of the black hole? Indeed, according to the general theory of star formation, black holes are the products of the end of the evolution of massive stars, with a minimum mass of three times the mass of the sun. However, stars are not the only way to form a black hole. When the universe was born, the density of matter and energy was so high that perhaps just a random fluctuation in the distribution of matter was enough to form a black hole. The black hole born in this way is called the original black hole, and there is no lower limit of mass. Physical simulations show that it is possible that its mass is only 10 times that of the earth.

Of course, this conjecture can also be combined with the previous conjecture that the primordial black hole could have been wandering in the universe, but happened to be captured by the sun's gravity as it passed through the solar system, affecting the orbits of those KBO. Physicists say we may be able to test this conjecture with moving gamma-ray and X-ray sources in space.

In 2020, in a study published in the Journal of Astrophysics Letters (The Astrophysical Journal Letters), Harvard astronomer Abraham Loeb (incidentally, he has put forward a number of "outrageous" theories) and undergraduate Amir Siraj came up with another outrageous explanation: there may once be a second star in the solar system.

The theory sounds radical, but it doesn't come as a surprise to some astronomers. "the vast majority of sun-like stars were members of binary systems at the beginning of their formation," said Hilaghi, author of the paper. " According to this theory, the sun had a companion of similar mass at the cluster stage, and then "a passing star moved the 'second sun' away through its gravity." Loeb said.

Where is the once second star in the solar system? Unfortunately, we can no longer track it. It could be anywhere in the Milky way. What we can speculate, however, is that if the star was indeed somewhere in the outer solar system, the paradox that Planet X could not form a planet could be explained-because there might have been another star.

Does Planet X really exist? However, not all astronomers believe that Planet X really exists. They point directly at the original reason for Planet X-the orbital consistency deviation of KBO. Some astronomers believe that the previous research is not rigorous. Specifically, the process of searching for observational KBO will introduce many deviations caused by observations, which have not been fully taken into account in previous studies. Such as the observation site of astronomers. The most powerful telescopes on earth are in Hawaii and Chile-because they have the best astronomical observation conditions in the world-but even in these places, astronomical observation conditions are seasonally distributed. As a result, astronomers can only observe KBO in certain directions. And for these limited KBO, astronomers are most likely to see these objects at their perihelion, because they are the brightest and easiest to observe, and the position of perihelion determines the orientation of the elliptical orbit, which can explain the specific deviation direction of the KBO orbit.

In 2017, the Astrophysical Journal (The Astrophysical Journal) published a four-year study on the Origin of the Outer Solar system Survey (OSSOS). They counted 830 new Kuiper Belt objects and simulated their orbits with computers. As a result, they can't say that the ninth planet doesn't exist, but there's not enough evidence to support it.

In 2022, two more astronomers published in the monthly Proceedings of the Royal Astronomical Society (Monthly Notices of the Royal Astronomical Society) analyzed data from the Infrared Astronomical Satellite (IRAS) and the AKARI Space Telescope, which are 23.4 years apart. If Planet X does exist, it should be able to move in the infrared images of the two moons. Astronomers found 535 candidates among them. But the infrared of these candidates is mainly interstellar gas, and none of them meets astronomers' imagination of Planet X. Astronomers even said bluntly: "No candidate is persuasive enough to guarantee a follow-up investigation."

Of course, this does not mean that astronomers have completely abandoned the search for Planet X. For example, the upcoming Vera C. Rubin Observatory,LSST Observatory is likely to find Planet X. It has higher detection accuracy and a wide field of view, and can patrol the entire sky every three nights. If Planet X does exist, the telescope may be able to detect its movement in repeatedly updated infrared night sky images.

Vera Rubin Observatory. Image source: Rubin Observatory / NOIRLab / NSF / AURA / B. Quint, however, for humans at present, how many planets are there in the solar system and whether Planet X exists or not is still an unanswered question.

Reference link:

Https://www.nature.com/articles/nature13156

Https://iopscience.iop.org/article/10.3847/0004-6256/151/2/22

Haunted Planet X, "Chinese National Astronomy"

Https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.051103

Https://iopscience.iop.org/article/10.3847/2041-8213/abac66

Https://iopscience.iop.org/article/10.3847/1538-3881/aa7aed

Https://academic.oup.com/mnras/article-abstract/515/4/4828/6652122?redirectedFrom=fulltext&login=false

Https://mp.weixin.qq.com/s/KVi9H47u-7cYA5tTw6Z3ww

Https://en.wikipedia.org/wiki/Planet_Nine

This article comes from the official account of Wechat: global Science (ID:huanqiukexue)

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