6 years is not a long time, but in the age of the Internet and new media, it is enough to make most people forget a small public case (in the United States, it is a big public case in the cultural world). And even those who have followed the koan may not be fully aware of its scientific implications.
Pluto‘s Strange Discovery History
Pluto was discovered on February 18, 1930, at 4 p.m. local time in Arizona, USA. This time point reminds the special channel of Pluto’s discovery – it was broad daylight at that time, can you see the stars in the sky?
In 1930, the golden age of American “civil science” astronomy had come to an end. That golden age was started by P. Lowell, a local astronomy enthusiast. He built his own observatory and served as the director, a self-organized astronomical magazine and his own editor-in-chief, and a self-organized astronomical society. His observatory is equipped with the best telescopes to observe the sky and employs professional astronomers for research. Lovell had two visions in his life: one was to observe the canals on Mars, and the other was to find “Planet X” beyond the orbit of Neptune. When Lovell died in 1916, the first vision had already made him famous, and the second had nothing. Now, of course, we know that the so-called “Mars Canal” is pure falsehood, but Lovell still has a long history in astronomy.
C. W. Tombaugh, a young man employed at the Lowell Observatory, continued to search for “Planet X” after the death of his employer. Uranus and Neptune in the solar system are inferred based on their perturbations to the orbits of the inner planets, and then they are observed in the inferred sky area. Lovell has always hoped to find “planet X” using the same method, but to the death. Tang Bo no longer had hope for this method, so he switched to a large-scale sky survey and photographic observation. This is a stupid method. It is to continuously take pictures of a large area of the sky, and then patiently compare the before and after photos to see if there are any in the background of stars. The celestial body that moves up. That’s why Pluto was discovered at 4 p.m. when Tombaugh was comparing photos. In the vast sea of stars, he actually found a small spot of light that moved quietly, and he discovered Pluto. Pluto was immediately designated as the ninth largest planet in the solar system, and Tombaugh became famous in history.
However, the peculiarity of Pluto’s discovery history is in its second half.
Pluto was originally thought to be of the same order of magnitude and mass as Neptune, which is about 18 times as massive as Earth. But in 1978, it was discovered that Pluto has a very large satellite Charon (Charon), which can help astronomers to calculate the mass of Pluto. The result is surprising – the mass of Pluto is only 0.24% of the mass of Earth ! The size of Pluto “has not yet been determined”, initially set at 6,400 kilometers in diameter, and now the newer data is 2,370 kilometers. Pluto’s orbital period is about 248 years, but since Pluto was discovered to the present, it has only orbited a third of its orbital period, and astronomers are far from witnessing it completes a full circle around the sun.
Fall of Pluto
For Pluto, the most tragic follow-up discovery came in the 1990s. As early as 40 years ago, the Dutch-American astronomer G. Kuiper proposed a hypothesis: There is a belt-like region composed of small ice-like celestial bodies at the edge of the solar system, which is called the “Kuiper Belt”. In fact, Pluto can be said to be in this zone. In 1992, astronomers at the University of Hawaii used optical telescopes to observe celestial body 1992QB1, or asteroid 15760, which is believed to be the first Kuiper Belt object. Six months later, the second one was discovered, and more and more Kuiper belt objects were discovered later, and the hypothesis of the “Kuiper Belt” was confirmed.
Small icy objects in the Kuiper Belt are constantly being discovered, and they are beginning to threaten Pluto’s status as a large planet—because Pluto is essentially the same kind of objects as these objects, only slightly larger. At that time, the discoverer of Pluto, Tombaugh, was still alive, and he vaguely felt the potential threat of Pluto, which made his famous history. In 1994, he wrote to the famous “Sky and Telescope” magazine, suggesting that these new discoveries should be named “Kuiper Small”. celestial body” to draw a line from Pluto.
Tombaugh died in 1997. In 2003, what Tombaugh was most worried about finally happened – astronomers discovered Eris (asteroid 136199) in the Kuiper Belt, which may be slightly smaller than Pluto but more massive than Pluto. Questions about the identity of Pluto’s large planet are so loud that the International Astronomical Union (IAU) can’t sit still.
IAU is a professional organization of astronomers around the world, with more than 10,000 members (the author also lists them). In 2006, which coincided with the annual meeting every three years, IAU set up a “Planet Definition Committee” to study the identity of Pluto. 7 people. The director of the committee was O. Gingerich, an expert in the history of astronomy, with whom the author also dealt, and whom we met at the 20th annual meeting of the IAU (Baltimore, 1988), who also graciously presented the author with a generous stack of Printed copies of his published papers.
There were only two definitions of planets at that time: 1. Orbiting a star; 2. Its own gravity was in the right range (large enough to be spherical, but not large enough to cause internal nuclear fusion – then it becomes a star) . Pluto fits both of these perfectly, and as a planet, it doesn’t seem to be a problem at all.
But it was at this time that someone submitted a paper “What is a Planet”, which proposed the third criterion for a planet: a planet must have the ability to clear its own orbit. This criterion gave Pluto the fatal blow.
The third criterion actually requires that the mass of the planet is large enough, because then the planet can rely on its own gravity to accommodate the small celestial body in its orbit as a satellite or directly swallow it up. For example, the earth empties its own orbit around the sun, and the other seven of the solar system All planets have done this. But Pluto is clearly far from being able to empty the Kuiper Belt.
The day of the final judgment has come. On August 24, 2006, the 26th annual meeting of the IAU (Prague, 2006) voted by an overwhelming majority (over 90%) of 424 delegates to remove Pluto from the planets of the solar system. , Pluto and the asteroids Ceres and Eris are classified as “dwarf planets”. There are only eight planets in the solar system.
Bragg’s decision came and sparked outrage in the United States because Pluto was “America’s planet” (the only one of the nine planets ever discovered by Americans). Prior to this, the “Pluto Planetary Identity Protection Association” had appeared. At this time, some lawmakers pushed legislation to “defend” Pluto in at least two states, and submitted a motion to the California State Legislature to “take away the planetary identity of Pluto against the International Astronomical Union.” condemned by a resolution”, while the New Mexico State Legislature passed legislation: “We declare Pluto a planet, and designate March 13, 2007, as Pluto Planetary Day in the State Legislature.” Various civil protests have emerged in large numbers, various sarcastic headlines have appeared in the media, and even news such as “Presidential Candidate Said: If Successfully Elected, Will Recognize Asteroid’s Planetary Status”.
Of course, all protests are in vain after all. After all, this is a scientific issue. After a while, the public, parliamentarians, and the media did not stop the “eight planets of the solar system” from being written into textbooks.
The scientific significance of the story of the rise and fall of Pluto
In the history of planetary science, none of the eight planets in the solar system today has such an encounter as Pluto: the truth is difficult to see, and many new discoveries constantly revise old cognitions, resulting in identity changes and causing a variety of disputes. What does this indicate?
At least one thing shows that the existing astronomical observation methods of human beings are close to the limit of capability when it comes to Pluto and the Kuiper belt. On July 14, 2015, the New Horizons probe launched by NASA arrived at the closest point to Pluto (still 12,500 kilometers away) and took the clearest picture of Pluto to date. However, we still know very little about this “dirty hockey puck”, which is about 5.5 hours light distance from Earth.
So, think of Pluto as the next astronomical benchmark—for any news that talks about astronomical discoveries in distant places (like 1,400 light-years away), let’s think about Pluto first.
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