Updated: Jan 17
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Pluto was the ninth planet of our solar system. Things were going exceptionally well for it until 2006, when International Astronomical Union said, 'Sorry, not everybody gets to be a planet'. Poor Pluto! But sometimes life isn't fair.
So, what changed in 2006?
Well, before 2006 there wasn't any strict definition of the word 'planet'. Instead, it was just an across-the-board given to celestial bodies that a) definitely weren't stars, b) also not asteroids or comets, and c) kind of large. But Pluto remained peculiar even with this definition. It was small, but not much farther out than one of the giant planets- Neptune. Also, it had an unusual orbit and a giant satellite. A giant satellite! Yes. Charon, one of Pluto's five natural satellite, is Pluto's largest satellite. At half the size of Pluto, Charon is the largest of Pluto's moons and the largest known satellite relative to its parent body. The same surfaces of Charon and Pluto always face each other. This phenomena is called as mutual tidal locking. Pluto-Charon is our solar system's only known double planetary system. Also, Pluto's orbit is more elliptical than those of other planets. Due to this Pluto is sometimes closer to the sun than Neptune.
Pluto and its moon.(left) Orbits of planets.(right)
Then in the beginning of 1990's we found that Pluto had a lot of friends. Friends with similar sizes and orbits. Are we really facing a reality with 20 planets? 200? 20,000?
So now it was time to enforce stringent laws in the wild west of planetary science. In 2006, with a vote at the meeting of the International Astronomical Union, three criterion were adopted as definition of a planet.
To be a planet, you must:
1) Orbit the sun.
2) Be large enough that your own gravity pulls you in a spherical shape.
3) Clear its orbital neighborhood of any debris.
Pluto fails 3), since it has such a large satellite and there's plenty of other junk hanging out nearby. In other words Pluto never became the boss of its own orbit.
Hence, Pluto was eliminated from the list of planets and characterized as a dwarf planet. But, many astronomers and planetary scientists dispute this definition and the resulting demotion of Pluto to a dwarf planet. Their contention: Pluto looks, acts, sounds, tastes, and smells like a planet. If you were to put it anywhere else in the solar system it would have been called a planet without a second thought. The argument continues but in the meantime , we have all accepted this definition of planets. Either way, Pluto will still be there, hanging out, being itself, regardless of what we call it. Check out my blog: https://prathashah.blogspot.com/