TOPICS: Story of Pluto

The common questions usually strike the minds of common people regarding celestial objects, including stars, planets, comets, asteroids, meteor, pulsar, galaxy etc and how they have been discovered far beyond our solar system, like the recently discovered TRAPPIST –1 system.

Since we grabbed our science book in our schooldays we were reading there were nine planets in the solar system. However, from August of 2006 Pluto has been removed from the list and the number of planets is reduced to eight.

What happened to the Pluto then? Inquisitive people might ask why this change was made?

The credit for this change goes to International Astronomical Union (IAU). It is the organization which determines the nomenclature of any celestial objects. It can modify, classify, and change the existing astronomical phenomenon.

It is an international association of professional astronomers active in professional research and education in astronomy. Among other activities, it acts as the internationally recognized authority for assigning designations to celestial bodies and any surface features on them. It is a member of the International Council for Science (ICSU).

Its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. It also looks for enthusiastic amateur astronomers and encourages them by providing membership and technical assistance.

Until 2006 there were nine planets, however, deep studies showed that there are some objects lying beyond the Neptune (called Kuiper belt objects) which orbit the sun as the planet does. And some of them such as Ceres are even bigger than Pluto.

So, there may be two possibilities, either these objects should be included in the category of planets or the definition of the planet should be broadened so that the new definition keeps the existing planets as such and Kuiper belt objects in different class.

With this in mind, space scientists put forward the new definition of a planet as a celestial object -- if it goes round the sun, has adequate gravity to keep it spherical and has its own independent path around the sun. However, Pluto failed to be housed in this definition as it couldn’t fulfill all the criteria of planets under this new definition.

Finally, Pluto has been kept under the new category called dwarf planets with Ceres, Haumea, MakeMake , Eris etc.