When and why was Pluto expelled from the list of planets?

Pluto is one of the most poorly studied objects in the solar system. Because of the great distance from the Earth, it is difficult to observe it in telescopes. Its appearance is more like a small star than a planet. But until 2006 it was he who was considered the ninth planet of the known Solar System. Why was Pluto expelled from the list of planets, what led to this? Consider everything in order.

Unknown to science "Planet X"

At the end of the XIX century, astronomers suggested that in our solar system there must be another planet. Assumptions were based on scientific evidence. The fact is that when observing Uranus, scientists found a strong influence on its orbit of foreign bodies. So, after a while Neptune was discovered, but the influence was much stronger, and the search for another planet began. It was called "Planet X". The search continued until 1930 and was crowned with success - Pluto was discovered.

The movement of Pluto was noticed on photographic plates made within two weeks. Observations and confirmation of the existence of the object beyond the known limits of the galaxy of another planet took more than a year. Clyde Tombaugh, a young astronomer from the Lowell Observatory, who initiated the study, in March 1930, announced the discovery of the whole world. So, in our Solar system for 76 years, the ninth planet appeared. Why did they exclude Pluto from the solar system? What was wrong with this mysterious planet?

New discoveries

At one time Pluto, ranked as a planet, was considered the last of the objects of the solar system. According to preliminary data, its mass was considered equal to the mass of our Earth. But the development of astronomy constantly changed this indicator. To date, the mass of Pluto is less than 0.24% of the Earth's mass, and its diameter is less than 2,400 km. These indicators became one of the reasons why Pluto was excluded from the list of planets. It is more suitable for a dwarf than a full-fledged planet of the solar system.

He also has many of his features that are not inherent in the ordinary planets of the solar system. Orbit, its small satellites and atmosphere are unique in themselves.

Unusual orbit

The orbits familiar to the eight planets of the solar system are practically round, having a slight inclination along the ecliptic. But the orbit of Pluto is a strongly elongated ellipse and has an inclination angle of more than 17 degrees. If we represent the model of the solar system, then the eight planets will rotate uniformly around the sun, and Pluto - to cross the orbit of Neptune because of its angle of inclination.

In view of this orbit, he orbits the Sun around 248 terrestrial years. And the temperature on the planet does not rise above minus 240 degrees. It is interesting that Pluto rotates in the opposite direction from our Earth, like Venus and Uranus. This orbit unusual for the planet was another reason why Pluto was excluded from the list of planets.

Satellites

Today, five satellites of Pluto are known : Charon, Nykta, Hydra, Kerber and Styx. All of them, except for Charon, are very small, and their orbits are too close to the planet. This is another difference from officially recognized planets.

In addition, Charon, discovered in 1978, half the size of Pluto itself. But for a satellite, it is too large. Interestingly, the center of gravity is outside of Pluto, and therefore it seems to swing from side to side. For these reasons, some scientists consider this object a double planet. And this also serves as an answer to the question of why Pluto was excluded from the list of planets.

Atmosphere

It is very difficult to study an object that is at an almost inaccessible distance. It is assumed that Pluto consists of rock and ice. The atmosphere on it was discovered in 1985. It consists mainly of nitrogen, methane and carbon monoxide. The presence of it could be determined by studying the planet, when it covered the star. Objects that do not have an atmosphere close the stars sharply, and those that have it gradually.

Because of the very low temperature and elliptical orbit, the melting of ice produces an antipark effect, which leads to an even lower temperature on the planet. After studies conducted in 2015, scientists came to the conclusion that the atmospheric pressure depends on the approach of the planet to the Sun.

Newest technologies

The creation of new powerful telescopes marked the beginning of further discoveries beyond known planets. Thus, in time, space objects were found within the orbit of Pluto. In the middle of the last century this ring was called the Kuiper belt. To date, hundreds of bodies with a diameter of at least 100 km and a composition similar to Pluto are known. The belt found was the main reason why Pluto was expelled from the planets.

The creation of the Hubble Space Telescope has made it possible to explore in greater detail outer space, and especially distant galactic objects. As a result, an object was discovered, called Eris, which was further away from Pluto, and in time - and two more celestial bodies, which in diameter and mass were similar to it.

The spacecraft AMS New Horizons, sent to study Pluto in 2006, confirmed many scientific data. Scientists have a question about what to do with open objects. Do they be classed as planets? And then in the solar system there will be not 9, but 12 planets, or the exclusion of Pluto from the list of planets will solve this question.

Revision of status

When was Pluto expelled from the list of planets? On August 25, 2006, the participants of the Congress of the International Astronomical Union (2,500 people) made a sensational decision to exclude Pluto from the list of planets of the Solar System. This meant that it was necessary to review and rewrite many textbooks, as well as maps of the starry sky and scientific works in this field.

Why was this decision made? Scientists had to reconsider the criteria by which the planets are classified. Long debates have led to the conclusion that the planet must meet all parameters.

First, the object must rotate around the Sun in its orbit. Pluto is suitable for this parameter. Although its orbit is strongly extended, it orbits around the Sun.

Secondly, he should not be a companion of another planet. This point also corresponds to Pluto. At one time it was believed that he was a companion of Neptune, but this assumption was discarded with the advent of new discoveries, and especially his own satellites.

The third point is to have enough mass in order to get a spherical shape. Pluto, although small in mass, but is round, and this is confirmed by photographs.

And, finally, the fourth requirement is to have a strong gravitational field to clear its orbit from other cosmic bodies. On this one point, Pluto is not suitable for the role of the planet. It is in the Kuiper belt and is not the largest object in it. Its mass is not enough to clear its way in orbit.

Now it is understandable why Pluto was excluded from the list of planets. But where do you enumerate such objects? For such bodies, the definition of "dwarf planets" was introduced. They began to include all objects that do not correspond to the last point. So Pluto is still a planet, although it's a dwarfish one.