Pluto, named after the god of the underworld in classical Greek mythology, is the last known and perhaps the least impressive member of the solar system. Revolving around the Sun in a period of 248 years, at an average distance of 3666 million miles (40 times as far away as the Earth), Pluto follows a curious orbit which is markedly eccentric so much so, that for part of its journey around the sun, it is actually closer than Neptune. Pluto seems to be a frozen body about 1500 miles in diameter and covered with frozen gases. From variations in the planets brightness it has been deduced that it revolves on its axis in about 6 days and 9 hours.

The existence of Pluto was predicted by an argument similar to the one Adams – Le Verrier had put forth in respect of Neptune on the basis of a perturbation noticed in the orbit of Uranus. It was noticed however, that even after taking Neptune into account, Uranus was slightly perturbed from its corrected orbit and that Neptune itself was slightly deviated. So astronomer Percival Lowell published his predicted position of the new planet Pluto in 1914. He tried many years in vain to discover it. But it was not until 1930, some years after Lowells death, that Pluto was traced.

However in the world of astronomy, Pluto has never commanded much respect or admiration. As we have seen, its very existence remained secret for a long time. Indeed, of all the planets that circle the Sun, Pluto generates the least amount of curiosity. The Voyager-2 Spacecraft which was expected to go past Plutos neighbour Neptune in 1989 was not expected to pause long enough even to take its picture.

Now, Pluto has become the target of the ultimate humiliation in the eyes of a group of astronomers, who are trying to take away even Plutos status as a planet itself and reclassify it as some sort of asteroid on the ground that its diameter seems to be much smaller than originally estimated.

Pluto is indeed a very small planet by any standards. But what is ironical is that every time someone focuses his attention on this planet, it seems to grow even smaller in stature and size, and because astronomers have now better telescopes and more accurate measuring methods they have been able to estimate Plutos diameter with greater accuracy than before. The latest assessment shrinking this figure from 1800 to about 1500 miles implies that this stellar body is smaller than even our little Moon orbiting our own planet. This would tempt us to place it in the category of a larger asteroid.

One of the difficulties in classifying a stellar body either as a planet or an asteroid is the fact that there is no universally accepted definition of a planet beyond the conventional viewpoint that it is a large body orbiting the Sun. What creates further confusion is the fact that there is certainly no official minimum size prescribed anywhere. For these reasons, Pluto has to be considered as an ‘in- between’ object; it can be considered too small to be a bonafide planet or too large to qualify as a typical asteroid. Large asteroids can, therefore, perhaps be classified as “minor planets” and referred to as “planetoids”. By the same reasoning, Pluto can be viewed, perhaps, as the biggest planetoid in the firmament.

Plutos history has never been without controversy. As indicated above it had a hard time being located at all. In the beginning of the last century, two American astronomers, Percival Lowell and William Pickering, suspected that there was another planet beyond Neptune. Both had made independent observations that pointed out to such a conclusion though neither was able to prove that anything was out there in reality. Only much later in the year 1930, another astronomer, in his early twenties Clyde Tombaugh, was able to photograph Pluto and confirm its existence. Tombaugh, in his eighties, was given the status of Professor Emeritus in the University of New Mexico. He was understandably irritated at astronomersrevisionist attempts to devalue the status of his favourite planet. He felt it was ridiculous that Astronomers seem to be eager to call Pluto an asteroid. According to him Pluto which is two-thirds of the size of Mercury and two times larger than any other asteroid, and also has a Moon of its own, by name Chiron, is eminently qualified to retain its original status as a planet. (In Tombaughs view asteroids are generally too small to have moons). In fact most are too tiny to have names—they are usually numbered. Some astronomers and heads of planetariums are inclined to agree with Tombaugh. With all the wonderful discoveries being made in the universe, they feel that a debate over Plutos already established status is a waste of breath and time. (According to them all that the new debate and analysis have revealed is that instead of Plutos diameter being the width of the United States, it is now only found to be the distance from New York to Denver.) As for the name change, they feel that it does not concern scientists. No wonder heads of planetariums are reluctant or unwilling to change or alter their stellar shows which depict the patterns of the heavens displaying configuration of galaxies, stars, planets (inclusive of Pluto!).

Notwithstanding the ideas of some astronomers regarding the lowering of Plutos status, the majority view is that while there are hundreds of Asteroids out there in space there is only one “Pluto”.

One mystery that remains is that even Pluto seems too small to produce the required effects on Uranus and Neptune. 

To sum up, there are only four inner solar system planets: Mercury, Venus, Earth, and Mars) and four terrestrial planets; Uranus and Neptune (the ice giants, containing mainly elements heavier than hydrogen and helium) and Jupiter and Saturn (the gas giants (containing mostly of hydrogen and helium).

Pluto, the ‘dwarf planet’, discovered in 1930 by Clyde Tombaugh, as stated above was initially classified as one of the solar system planets. However, it is now considered to be one of the largest known members of the collection of icy bodies on the outer fringes of the solar system, known as the Kuiper belt. When a body of scientists decided a formalised definition for the term “planet in 2006, Pluto was demoted from its planetary status.

The International Astronomical Union, defines a planet as “a celestial body that has three qualities:

 (a) it should  be in orbit around the Sun,

(b) it should have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,


 (c) it has cleared the neighbourhood around its orbit.”

However as Pluto is part of the Kuiper Belt, and has therefore not met the third criterion, it is no longer considered a planet. Instead, it is classified as a ‘dwarf planet’. Eris, Ceres, Haumea, and Makemake are four other dwarf planets.

Pluto with an atmosphere, stark surface features, and at least five moons, is the most complex ‘dwarf planet’ we know. The New Horizons spacecraft, which was launched on Jan. 19, 2006 and carried out a six-month-long reconnaissance flew past Pluto and its moons in summer 2015, collecting and transmitting useful data to the earth.

But before flying past Pluto, It had a brief encounter with an asteroid and proceeded towards Jupiter making its closest approach on February 28, 2007, at a distance of 2.3 million kilometres (1.4 million miles). After its transmission of data in respect of Pluto in 2015, it moved towards the edge of the solar system. It is the fifth Spacecraft to have acquired the escape velocity necessary, to leave the solar system.

Pluto remains. a riddle, wrapped in an enigma, inside a mystery” and the world needs another Kuiper or Herschel to find the key to solve the problem by making further discoveries in respect of these heavenly bodies.


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