This year marks the 90th anniversary of the discovery of Pluto.
  Pluto was once listed as one of the nine planets in the solar system, and was later expelled from the ranks of large planets and downgraded to a dwarf planet. However, Pluto has never faded out of people’s sight. In July 2015, in a close-up photo of Pluto taken by the US “New Horizons” probe, a big love pattern once again made Pluto a hot topic.
Appearance-Discovery Under the Expectations

  Before Pluto was discovered, people had found 8 planets around the sun, and the last discovered Neptune was also called “the planet on the tip of the pen.” French astronomer Le Vieux used Uranus’ orbit to be affected by the gravitational effects of other celestial bodies and calculated the location of another planet that might exist on its periphery. He informed John Galle of the Berlin Observatory of his calculations and asked him to help with the search. Sure enough, in 1846, Galle and his student Heinrich Darest discovered the trace of Neptune, and its actual position was only 1° deviation from the position estimated by Levier. As a result, Neptune became the first planet whose position was obtained through mathematical calculations and then confirmed by telescope observation, so it was dubbed the “planet on the pen tip”.
  After Neptune was discovered, it was discovered that Neptune’s gravitational influence could not fully explain the changes in Uranus’ orbit. Therefore, it is speculated that there should be other celestial bodies moving in the periphery, affecting the orbits of Uranus and Neptune. Many scientists have given their own results, all wanting to use their own calculations to replicate the next “planet on the pen tip” legend after Neptune. But the greater distance and smaller orbital deviation will undoubtedly make it more difficult to find new planets beyond Neptune.
  One name that has to be mentioned among many people who are struggling to search for new planets is Parcival Lowell. This wealthy Bostonian founded the Lowell Observatory in Flagstaff, Arizona in 1984. This is also the first time the observatory was built at a height away from humans in order to obtain a better observation environment. Altitude area. Lowell used the telescope on the observatory to devote himself to two obsessive astronomical tasks, one is to find traces of canals on Mars, and the other is to search for unknown planets that may exist outside Neptune, which he called Planet X .
  The First World War and the dissatisfaction of astronomical research caused a huge blow to Lowell’s body and mind. He unfortunately died of a stroke in 1916, and the Lowell Observatory’s plan to search for Planet X was also interrupted. It was not until 1929 that the 23-year-old Clyde Tombaugh recruited by the Lowell Observatory continued this work, and the mysterious planet X was revealed. Pluto was discovered by Tombaugh at about 4 pm on February 18, 1930. Everyone will be curious about how it is possible to see the stars when the sky is not dark at around 4 pm? In fact, Tombaugh did not observe Pluto directly with a telescope, but found Pluto through a special method.
  Tombaugh discovered that Pluto uses an astronomical device called a “flicker contrast”, which can quickly switch back and forth between two pictures of the same starry sky taken at different times, using visual residual phenomena to make the human eye perceive two The slight difference in photos is a bit similar to the two-picture finding difference game we often play now. On the afternoon of February 18, the diligent Tom Bo found a small bright spot that was moving in Gemini by repeatedly comparing the two photographic negatives taken on January 23 and 29. This was later named Pluto. The ninth planet.
Controversy-New celestial bodies that are messing up

  Since the discovery of Pluto, controversy about it has continued to arise. Throughout the 20th century, astronomers have been committed to determining its orbit and mass. The measured mass of Pluto is very small, too small to have too much influence on Uranus’ orbit. Other new scientific discoveries in the solar system are also shaking Pluto’s status as the ninth largest planet.
  In 1978, Pluto’s first satellite, Charon, was discovered by the telescope of the United States Naval Observatory in Flagstaff, Arizona. Charon’s discovery allowed astronomers to better determine the masses of two stars by revolving them. As a result, the mass of Pluto was smaller than previously estimated, while Charon’s mass was ten times that of Pluto. One part, the radius reaches half of Pluto. The two orbits also formed a 1:1 tidal lock orbit, which means that Pluto and its moon Charon have only one side of each other orbiting each other, which is also unique among the planets in the solar system. It can be said that Charon’s various properties have shaken Pluto’s planetary status.
  In 1992, the field of solar system research ushered in an epoch-making discovery. Professor David Juitt of the University of Hawaii and his graduate student Lixing Liu discovered an icy celestial body outside Neptune-1992QB1. This celestial body moved in the area predicted by the famous astronomer Gerard Kuiper and became a human being. The first Kuiper belt object. Since then, astronomers have discovered more than 1,000 Kuiper Belt objects. Among them, Eris, Makemake, and Haumea are all about the size of Pluto, and satellites have been found around 10% of Kuiper belt objects.
  We must know that Pluto itself is also located in the Kuiper Belt. When more Kuiper Belt objects are discovered, Pluto does not appear to be a maverick in it. If it is a planet, should these newly discovered Kuiper Belt objects of similar size also be defined? For the planet? More new discoveries have brought not only the expansion of the understanding of the outer boundaries of the solar system, but also a real threat to Pluto’s position in the solar system.
  In addition, many properties of Pluto itself are also different from the other eight planets. For example, the mass of Pluto is very small, only 5% of the mass of Mercury, the smallest of the eight planets. Its orbit is not a near circular orbit, but a flat ellipse, and there is a cross between the orbits of Neptune adjacent to it. In addition to being very flat, Pluto’s orbit is also more inclined, and its angle with the ecliptic plane of the solar system is 17°, which is much larger than that of Mercury, which has the largest orbital inclination among other planets. Some astronomers and astronomy science workers are also constantly thinking about how to better define Pluto’s status in the solar system.

  At the 26th International Astronomical Union Congress in 2006, 424 participants voted on the spot to pass the new definition of planets, and Pluto was officially excluded from the ranks of planets.

  At the end of the 20th century, the American Museum of Natural History decided to rebuild the historic Hayden Planetarium. When the first curator of the new museum, Neil Tyson, organized the design of the venue, he racked his brains on how Pluto would arrange the location in the venue. In the solar system exhibition, Tyson was struggling to find out where to attribute Pluto. He even organized a public debate and invited five authoritative experts with different positions to explain whether Pluto should be displayed as the ninth planet. The discussion did not reach the final result. However, Hayden Planetarium, led by Tyson, decided to introduce the celestial bodies of the solar system in a unique way, that is, instead of listing the planets in order according to the previous practice, but according to the nature, the solar system has been discovered at that time. Many celestial bodies are classified and displayed: the sun is displayed separately as Big Brother; the next terrestrial planets are Mercury, Venus, Earth, and Mars; the Jupiter, or gas giant planets, are Jupiter, Saturn, Uranus, and Neptune; Pluto is due to its weight. Naturally, the natural disadvantage of is not classified into any of the above categories, but is placed in the Kuiper Belt objects; the outer part is the Oort Cloud full of active comets.

  This sort of display method, which seemed to be the most scientific and reasonable at the time, caused an uproar after the opening of the Hayden Planetarium in 2000. The children were confused because they could not find Pluto, the ninth planet in the book, when they visited the Hayden Planetarium. The media also made a fuss about it. The public’s discussion on the status of Pluto also shocked the authoritative organization in the astronomy community. The International Astronomical Union was established in 1919. This organization is responsible for the naming of all celestial bodies, and Pluto’s identity is ultimately determined by it.
Downgrade-a vote that attracts worldwide attention

  The controversy caused by Pluto is not only among the public, but the opinions of scientists are also different. After more than two years of committee deliberation, the International Astronomical Union still couldn’t reach an agreement on how to define a planet, so a planetary definition committee was established. Experts from the Planetary Definition Committee put forward the definition of planets through discussion, and submitted them to the International Astronomical Union Conference for deliberation. After several rounds of discussions, the definition of planets was finally submitted to all scientists present at the conference for voting.
  The latest definition of a planet consists of three core elements: a celestial body must revolve around the sun, have enough mass to make itself close to a spherical shape, and can clear other celestial bodies in its adjacent orbit, before it can be called a planet. In this definition, Pluto in the Kuiper belt, its orbit is also full of other small ice balls-Kuiper belt objects. The new definition of planets actually blocks Pluto from the ranks of planets.
  On August 24, 2006, at the last day of the 26th International Astronomical Union Congress in Prague, the capital of the Czech Republic, 424 participants present voted on the new definition of planets by holding yellow cards in agreement. There was no accurate counting of votes at the scene, but with an overwhelming majority of votes, the new definition of planet was passed. Pluto was officially excluded from the ranks of planets and was redefined as a class of celestial bodies-“dwarf planets.” Incorporated into the ranks of dwarf planets together with it, there are several large Kuiper belt objects we have introduced above, and an asteroid, Ceres.

  Although the International Astronomical Union officially downgraded Pluto to a dwarf planet, the results of the vote also attracted strong protests from some planetary science organizations. They believe that the 424 astrophysicists participating in the voting cannot represent all the more than 2,000 astrophysicists participating in the conference, let alone the tens of thousands of members of the International Astronomical Union. They even organized to publish a petition of protest and solicit signatures from supporters.
  Among the people who are dissatisfied with the voting results, there are all kinds of people, and the reasons for their opposition are also varied. What some people oppose is that the International Astronomical Union simply and rudely redefines the concept of planets and hastily voted on it. There should be a more enlightened and gentle solution. The congressman from New Mexico, the hometown of Pluto discoverer Tom Bo, passed a commemorative bill by Congress to declare Pluto as a planet within the state to express dissatisfaction with the voting results. In short, the downgrade of Pluto by the International Astronomical Union goes far beyond pure science, but penetrates into all aspects of society.
Rebirth-“Comparative Heart” Earth

  Over time, the public’s attention to Pluto’s demotion has been gradually replaced by other news and events, and with the emergence of new scientific discoveries and the spread of knowledge, more people have accepted that Pluto has become a dwarf planet. fact. Just when most people have forgotten the controversy about Pluto, in July 2015, NASA released a close-up picture of Pluto, which brought this controversial celestial body back into people’s field of vision. . The “New Horizons” probe launched in 2006, after more than 9 years of long interstellar travel, flew over Pluto at close range. On the Pluto “document photo” taken, a big love pattern shocked the world. This picture is almost a household name, so everyone will love it at first sight. It is hard to imagine that in the dark and deep part of the solar system, Pluto in an icy environment has such a heart-warming pattern on its surface. This celestial body, which has experienced great ups and downs, returned to the eyes of the world in such a way when many people almost forgot about it. “Bixin” earth people, and more scientific results have been discovered at the same time, it is undoubtedly a gorgeous turn. The heart-shaped area is named “Tombo Zone” to commemorate the discoverer of Pluto. Scientists discovered that this area is a plain rich in nitrogen ice. The “New Horizons” probe that photographed Pluto also carried Tom Bo’s ashes.
  The ups and downs of Pluto’s experience has attracted the attention of the world because of the changes in his life experience. Similar to the stories before and after it was revised as a dwarf planet, it can be said to be everywhere in astronomy research and even more extensive scientific research.