What is a planet? Disputes continue

If you know what a planet is, then you know more than astronomers. Because they are not sure about the definition of this term. For example, some consider Pluto to be a planet, others not.

Изначально так называли Марс, Венеру, Юпитер, Saturn, Mercury. By the way, the names of the planets came to us from Greek and Roman mythology. The earth was for the ancient special, different from other celestial objects. The moon and the sun, too, were ranked as “wandering bodies” of a somewhat different nature. Have you ever wondered why we have one day off in seven days? This is not reflected in the Russian language. But in French, Italian, for example, there is a clear connection between this “magnificent seven” and the days of the week: Monday - Moon, Tuesday - Mars, Wednesday - Mercury, Thursday - Jupiter, Friday - Venus, Saturday - Saturn, Sunday - Sun .

Uranus was discovered in the 18th century.Then, thanks to the studies of Le Verrier and Adams, Neptune (in the 19th century). In 1930, the world learned about the existence of Pluto. This discovery was made by Clyde Tombo. Pluto is still called the ninth planet. Is it so? In order to answer this question, it is necessary to understand what is a planet?

Само это понятие сформировалось у нас исторически.In the sky, we see five planets with the naked eye. And everything would have been much more complicated if the asteroids were brighter. Astronomers have agreed to call a planet an object that is in orbit of a star, moreover, it must be large enough to become a sphere due to gravity. Many comets and asteroids have very strange forms.

There was no exact definition of “what is a planet”.But nevertheless for Pluto stuck just such a name. In fact, this is a very strange object, and it is very different from the rest of the major planets. Its orbit is somewhat more elongated. As it turned out, Pluto is very small. Far less than astronomers had previously believed. All the planets of the Solar system are located "in height": 4 terrestrial groups at the beginning, then the giant planets. Pluto here clearly does not fit.

Then they discovered the satellite of Pluto - Charon, which is almost the same size. This is also somewhat atypical: all planets have a much smaller satellite.

Kuiper (American astronomer) suggested thatbeyond Neptune is the asteroid belt. This was another blow to Pluto’s “status”. This belt really is! Currently it is called the Kuiper belt. The bodies in it are somewhat different from asteroids. But very much like Pluto, only smaller in size. Now it became clear to all that Pluto is one of the large Kuiper belt objects. But while the former name is preserved. Scientists, for the most part, are conservative people, so they decided to leave everything as is for now.

And yet, what is a planet? Soon this question will become very relevant. Because it is known that the planets of other stars are already opening.

The main parameter is mass.Smaller objects are asteroids, more massive objects are stars. Everything is clear with the stars. They must have a high temperature for thermonuclear processes to occur. The planet in its orbit should be one, if there are many objects (“belt”), then these are asteroids.