The New Horizon spacecraft of NASA in July 2015, flew past the earlier considered smallest planet Pluto, and the encounter created history. In the year 2006, the International Astronomical Union (IAU) made an announcement of putting forth a redefinition for the word “planet.” The redefinition eliminated many of the objects, encompassing Pluto. The scientists now have the thoughts that the decision was not correct and a more useful and logically sound definition of the word “planet” would encompass a lot more worlds.
As said by the planetary scientists they have spent a long time in the study and exploration of the objects, which orbit the stars, and they use the word “planet” to define any world exhibiting these qualities. When they witness a world as that of the Pluto exhibiting a lot of similar features such as- the nitrogen glaciers, icy mountains, and the blue sky having smog layers, the scientists cannot help themselves from landing up calling out “planet” for describing it and/or comparing it to the other known planets.
The scientists even end up using the word “planet” for describing the biggest “moons” in our Solar System. The word “moon” points out the fact, they revolve around the other worlds that themselves revolve our star. However, when any other world is discussed like that of the Titan of the Saturn that is bigger than that of Mercury and features mountains, rivers, clouds, lakes, and dunes, the scientists call it as “planet” in their conferences.
Basically, the planetary worlds are those which are big enough to pull themselves by their gravity into the form of a ball. Under a fixed size, the worlds get lumpy as the strength possessed by the rocks and ice prevent rounding by their gravity. By this method, the scientists distinguish the planets and the non-planets and with the same technique, Ultima Thule was not regarded a planet even before the New Horizons spacecraft arrives.
However, the need to redefine the word “planet” came up due to two thrilling findings regarding the universe. Firstly, there are a large amount of planets beyond the Solar System known as “exoplanets” that orbit almost all the stars. Secondly, there is a massive amount of tiny icy objects that orbit the biggest star of the Solar System out in the realm of Pluto, ahead of the belt of the “terrestrial planets”, the “ice giants”, and the “gas giants.”
These findings forced to question as to which objects found orbiting the other stars could be called planets. Some of them are nearly stars themselves and are known as “dwarf stars” and it is somewhere sensible to put tiny icy worlds as that of the Pluto to another subcategory called “dwarf planet.”