Pluto’s status has been questioned since the late 1970s, when the distant planet 2060 Chiron was discovered and astronomers also learned about its lower mass more precisely.
In June 2008, the International Astronomical Union decided that from Pluto there will now be collective names of approximately the same size – the so-called “plutides”.
less than the moon
There were more arguments about why Pluto ceased to be a planet. Above all, it was a correction of a nearly century-old error—when Pluto was discovered, it appeared to be larger than Earth and about seven times more mass; So it makes sense to belong to the planets. However, astronomers now know that Pluto is smaller than the Moon.
After the year 2000, the need to define the planet in some way became even more pressing. At that time, the discovery of the so-called exoplanets began to increase – planets close to exotic stars, but also larger planets on the borders of the solar system.
Scientists were just waiting to find an object larger than Pluto there. This happened in 2005, when astronomers discovered an object called UB313.
Since it was not certain whether it was a planet or another type of thing, it was not allowed to be named after a deity according to the rules in force at the time – so scientists called it Xena. Only later UB313 got the name Eris after the Greek goddess of strife.
Then there were only two options – either to expand the solar system with more bodies, or to stay with eight indisputable planets, thereby excluding Pluto from this “elite club”.
They sent him an investigation
At the age of 24 in 1930, American astronomer Clyde William Tombaugh discovered Pluto, which he observed at the Lowell Observatory in Arizona. The cosmic body is named after the god of the underworld, Pluto (Greek Hell). Then Pluto became the ninth planet in the solar system.
Pluto, like other objects in the Kuiper belt, is mainly made of stone and ice material. It is a relatively small object with a mass of about one-fifth of the mass of the Moon and one-third of its size.
Pluto has five known moons. The largest of them – Charon – was discovered in 1978, and the other two – Nix and Hydra – did not follow until 2005. The last months – Kerberos and Styx – were discovered between 2011 and 2012.
In July 2015, the US spacecraft New Horizons reached a distance of 12,500 km from Pluto. At that time, the spacecraft took pictures showing craters, mountains and ice formations located in an area about 80 kilometers wide. At the same time, a number of red areas, possibly frozen water, can be seen on the surface of the dwarf planet.
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