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How come a star is demoted

Pluto, the ninth planet, may not be a planet at all

By: Avi Blizovsky (published at the time by Baharez)

"Leave it in its place as a planet, leave it alone," responds with a smile the chairman of the Israeli Astronomical Society, Yigal Fatal. He is referring to the planet Pluto, which has recently been at the center of a loud debate in the astronomical community - a debate about its very status as the ninth planet of the solar system.
The journal "THE ATLANTIC MONTHLY" reported in its last issue that Pluto may lose its status as a planet. In recent years, reports reporter David Friedman, after countless studies and photographs by space telescopes, it became clear how small Pluto is. At the time of its discovery, in 1930, a size equal to that of the Earth was attributed to Pluto. In the 60s, he cut the textbooks in half. In '78, astronomers discovered that Pluto had a relatively large moon, whose brightness was mistakenly mixed with that of the planet. When this was taken into account, Pluto was left with a diameter of about one-sixth that of the Earth, 2000 km, which is even half the diameter of the planet Mercury, previously considered the smallest planet in the solar system.
Seven moons in the solar system are larger than Pluto itself. In addition, it is significantly different from its stellar neighbors at the edge of the solar system. The four terrestrial planets are rocky and medium in size, the other four planets are gas giants. What is a small ball of ice doing at the edge of the solar system? A surprising answer to this question has been received in recent years. It turns out that Pluto is only one of about 60, and some claim that there are hundreds and thousands - small bodies, like comets, that reside in the belt that extends beyond the frame of the planets. But this discovery, which provides an answer to a long-standing mystery, involved another question, more painful to many astronomers: Is Pluto really a planet? A growing number of scientists studying the solar system today include Pluto in the family of asteroids and comets. Others feel offended by the idea, insisting that even though his identity has changed, demoting him would be an insult to astronomy, and no less, would cause public confusion. Indeed, in the end, today the debate mainly revolves around a sentimental matter: the facts are known, we have to agree on the name and status.
According to Fatal, the considerations in favor of disqualification are many. Pluto's small size, much smaller than the planet Mercury, our Moon, the four largest moons of Jupiter and Titan. In fact, it is more or less the size of Triton, a moon of the planet Neptune, and quite similar to it in its specific gravity and composition (ice). In terms of specific gravity and size it has the characteristics of a moon. The inclination of its orbit is 17 degrees relative to the plane in which the Earth and most of the other planets (except Mercury whose inclination is seven degrees) orbit the Sun. This plane is called the Malka plane (from the language of defects).
Its orbit is also very elliptical. Currently, the farthest planet from the solar system is Neptune. Pluto's orbit is so long that it intersects with Neptune's orbit, and only in the year 2000 will it again become the most distant planet. Its specific gravity, 2.1 grams per cubic centimeter, is lower than that of the terrestrial planets (5-4 grams per cubic centimeter). The gaseous planets are around 1 gram per cubic centimeter. In this respect, Pluto is similar to the large moons of Jupiter, Uranus or Neptune. More ice moon than planet. The orbit is more like that of a comet than that of a planet. Pluto also differs in composition from the distant planets, which are mostly gas giants. the little one
Among them, Neptune, about 25 times larger than Pluto in terms of characteristics, therefore, it is more likely to say that Pluto is a giant comet, than a dwarf planet. Even the fact that it has a moon, which until recently was considered a characteristic of a planet alone, does not mean anything, since recently it was discovered that the asteroids Ida and Tactile have moons. Satellites (moons) can also be a comet.
The fact that Pluto has a moon, discovered in 1969 and called Charon, does not prevent it, then, from being a comet or a large asteroid. Beyond Neptune's orbit lies the Kuiper belt. This is the region from which comets come. Pluto also resides there. Recently, comets hundreds of kilometers in diameter have been discovered there. For example 1996TL66 with a diameter of about 500 km. The diameter of Pluto is about 2000 km, the diameter of its moons is about 300 km.
If so, why not demote Pluto? The reasoning sounds a little strange: parental right. After all, argue the defenders of Pluto, this is a debate about semantics, not about facts. And since the public has gotten used to seeing Pluto as a planet, there is no point in suddenly changing the situation. The followers of Pluto also do not spare slander from other causes: even among the asteroids there are some that are rocks, and others metallic. There are also several types of gaseous and rocky planets. So why not say that Pluto is simply a model of a planet of the third type - only that the others similar to it we have not yet discovered because they are far away. "I'm in favor of keeping it, if only because starting to teach now that the solar system has eight planets doesn't work for me," concludes Fatal.
At the head of those demanding to remove Pluto from the family of planets is Brian Marsden, who served for 30 years as a senior member of the International Astronomical Union - a body whose mission was to report on the discovery of comets and asteroids. But even Marsden, as he lays out his arguments, begins to stutter. "Pluto is a long-standing myth that has been difficult to eliminate," he admitted in an interview with the magazine.
No, Marsden has no grudge against Pluto. On the contrary, he spent most of his life trying to calculate the complicated orbits of the small bodies in the solar system, which made him fond of the only planet whose position causes it to circle the sun in an orbit that takes hundreds of years, and which is difficult to predict exactly. Either way, Marsden says, people won't find Pluto's planetary history fit for celebration, especially if they learn the circumstances in which it was given the top rank.
Percival Lovell, a Brahmin priest from Boston and an amateur astronomer, became, towards the end of the 19th century, obsessed with his search for a planet he called "X". After assuming that the observed disturbances in the orbits of Uranus and Neptune indicate the existence of a massive planet - he built an observatory in Arizona, partly to locate that X. Even after Lovell's death in 1916, without having discovered what he wanted, the observatory continued to operate. The young astronomy enthusiast Clyde Tombaugh, who worked at the observatory, succeeded in 30 in casting X out of a thick field of stars, in an operation that is still considered one of the most impressive of astronomical observation. The name Pluto was decided because it contains the letters - PL, the initials of Percival Lovell. The World Astronomical Union, influenced quite a bit by the euphoria that prevailed in the USA following the discovery, hastened to give Pluto an official nod as a planet. It was a reasonable decision then. According to the observatory's claim, Pluto is close to the place where Wall predicted the existence of Planet X. At that time it was believed that if the object was so small, it could not be seen from Earth. So they assumed it was big. In retrospect, it turns out that you see it because it is mainly composed of ice, which reflects sunlight similar to comets. And anyway, Pluto is not an X. It is too small to cause deviations in the orbits of the outer planets, as Lovell believed, whose observations were probably mistaken. It was, then, pure coincidence. Pluto happens to be in an area where they mistakenly thought there should be a planet. and therefore was included in the list of planets.

Pluto - not really a planet?

The International Astronomical Union will probably be asked to intervene in the debate that spans the community of astronomers: is the planet Pluto indeed a planet, or should it be downgraded - and draw the map of the solar system known to us, so that it only includes eight...
The International Astronomical Union will probably be asked to intervene in the debate that spans the community of astronomers: is the planet Pluto indeed a planet, or should it be demoted - and draw the map of the solar system we know, so that it only includes eight planets, not nine.
Pluto was discovered in 1930 by Clyde Tombaugh, an amateur astronomer, at an observatory in Arizona, USA, and since then it has been considered one of the nine planets in the solar system. The Atlantic Monthly magazine reported in its last issue on a move that leads a senior American astronomer, Brian Marsden, to remove Pluto from the group of planets. Marsden and other astronomers rely on a long series of findings, which they claim deny Pluto the title. Pluto's size, composition, specific gravity and orbital inclination are all significantly different from those of the other known planets (Hema, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune).
Although there is no dispute about the findings, many astronomers are against the initiative. Their claims are mainly based on sentimental and traditional reasons. Pluto has been considered a planet for 68 years, they say, and there's no point in changing it now. The chairman of the Israeli Astronomical Society, Yigal Fatal: "I'm in favor of keeping it, if only because it doesn't work out for me to start teaching now that the solar system has eight planets."

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