Solar System

Pluto was discovered in 1930 by Clyde W. Tombaugh at Lowell Observatory in Flagstaff Arizona. Astronomers have long predicted that there would be a ninth planet in the solar system, which they called Planet X. Only 22 at the time of Tombaugh was given the difficult task of comparing photographic plates. These were two pictures of an area of sky, taken two weeks apart. Any moving object, an asteroid, comet or planet that seems to jump from one image to the next.

After a year of observations, Tombaugh finally discovered an object in the right way, and declared that he had discovered Planet X. Because they had discovered Lowell team was allowed to call it. They settled on Pluto, a name suggested by a 11-year-old school girl in Oxford, England (no, it was not named after the Disney character, but the Roman god of the underworld). 

The solar system now had 9 planets: 

Astronomers were not sure about Pluto's mass until the discovery of its largest moon, Charon, in 1978. And by knowing its mass (0.0021 Earth), they could more accurately measure its size. The most accurate measurements now give the size of Pluto at 2,400 km (1,500 miles) across. Although this is small, Mercury is only 4,880 kilometers (3,032 miles) across. Pluto is small, but it was considered larger than any previous orbit of

Neptune. 

In recent decades, powerful new ground-and space-based observatories have completely changed the earlier understanding of outer solar system. Instead of being the only planet in the region, like the rest of the solar system, Pluto and its moons are now known to be just a good example of a collection of objects called the Kuiper Belt. This area extends from the orbit of Neptune out to 55 astronomical units (55 times the distance from Earth to the sun). 

Astronomers estimate that there are at least 70,000 icy objects with the same composition as Pluto, measuring 100 km in diameter or more in the Kuiper Belt. And under new rules, is Pluto not a planet. It's just another Kuiper Belt object. 

Here's the problem. Astronomers had been appearing more and more objects in the Kuiper Belt. 2005 FY9, discovered by Caltech astronomer Mike Brown and his team are only slightly smaller than Pluto. And there are several other Kuiper belt objects in the same classification. 

Astronomers realized that it was only a matter of time before an object larger than Pluto was discovered in the Kuiper Belt. 

And in 2005, Mike Brown and his team lost bomb. They had discovered an object more distant than Pluto's orbit, which was probably the same size or larger. Official name 2003 UB313, the object was later identified as Eris. Since its discovery, astronomers decided that Pluto's size is approximately 2,600 kilometers (1,600 miles) across. It also has approximately 25% more mass than Pluto. 

As Eris is larger, is made of the same ice / rock mixture, and more massive than Pluto, the concept that we have nine planets in the solar system began to fall apart. What is Eris, planet or Kuiper Belt object, what is Pluto, for that matter? Astronomers have decided that they would take a final decision on the definition of a planet to XXVI General Assembly of the International Astronomical Union, which was held from 14 August to 25 August 2006 in Prague, Czech Republic. 

Astronomers from the association got the opportunity to vote on the definition of planets. A version of the definition would have actually increased the number of planets to 12, Pluto is a planet and Eris was so smooth and Ceres, which was intended as the largest asteroid. Another proposal, which kept the total to 9, which defines the planets, who only knows the ones we know, without any scientific justification, and a third would drop the number of planets down to 8, and Pluto will be out of planet club. But then ... what is Pluto? 

Ultimately, astronomers voted on the controversial decision to demote Pluto (and Eris) down to the newly created classification of "dwarf planet". 

Is Pluto a planet? Not fall? For an object to be a planet that is needed to meet these three requirements, which the IAU: 

It should be in orbit around the sun - yes, then maybe Pluto is a planet. 

It is necessary to have enough gravity to pull itself into a spherical shape - Pluto ... check 

It is necessary to have "cleared the neighborhood" of its orbit - Uh oh. Here is the rule

breaker. According to this, Pluto is not a planet. 

What does "cleared its neighborhood" mean? As planets form, they become the dominant gravitational body in their orbit in the solar system. As they interact with other, smaller things that they either hold them or throw them away with their gravity. Pluto is only 0.07 times the mass of other objects in its path. Earth, by comparison, has 1.7 million times the mass of other objects in its path. 

Any item not meeting these 3rd Criteria considered a dwarf planet. And so, Pluto is a dwarf planet. There are many objects with similar size and mass of Pluto pushed around in its orbit. And until Pluto goes into many of them and gains mass, it will remain a dwarf planet. Eris suffer the same problem. 

It is not impossible to imagine a future, though, when astronomers discovered a large enough object in the distant Solar System that could qualify for a planet cap status. So our Solar System will have 9 planets again. 

Although Pluto is a dwarf planet, and no longer officially a planet, it will still be an interesting target for investigation. And that is why NASA has sent its New Horizons spacecraft from visiting it. New Horizons will reach Pluto in July 2015, and captured the first close-ups of (dwarf) planet's surface. 

Space enthusiasts will admire the beautiful and remote and Pluto, and the painful deplaneting memories will fade. We just want to be able to appreciate it, as Pluto, and not worry about how to categorize it. At least now you know why Pluto was demoted.