Solar: The question sounds easy, but the answer bothers a lot of people. Anyone born before 2000 will answer nine. And whoever was born later will probably answer eight.
The truth is that since the 2006 International Astronomical Union (IAU) meeting, the correct answer is 8. We have 8 official planets in the Solar System. 15 years ago, Pluto was reclassified as a double dwarf planet. But he sends his regards that doesn’t matter to him. In fact, nothing has changed for the celestial object. Pluto physically follows in the same way. In the same orbit, with the same mass, exactly the same. We just classify it differently.
But after all, why do we need a reclassification?
With the technological advancement of telescopes, more and more objects were discovered in the Solar System. And many of these were similar to Pluto. This became a problem as it would be impractical for us to study the Solar System with more than 50 planets. Then, in 2006 an official classification of planets was arrived at. And what the object needs to have to be classified as such. These are:
Need to orbit a star. In our case, the Sun.
It needs to be round. Only an object with sufficient mass achieves hydrostatic balance, acquiring a round shape. So in other words, it needs to have enough mass.
You must have cleared your orbit. In other words, be the dominant object. Planets have moons, this is not a problem as long as the planet is hierarchically the dominant star. And that is not the case for Pluto.
Pluto has a companion, Charon, who until then was considered his moon. It turns out that Charon has a mass very close to that of Pluto. Close enough for us to say that Charon is not orbiting Pluto, but they orbit each other and do a dance around the center of mass. After 2006, the system was considered “double dwarf planets”.