We once learned it as:
My Very Educated Mother Just Showed Us the Nine Planets
This meant Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune and Pluto
And now the revised version goes like:
We have always known Planet Pluto as the youngest sibling among the big giants in the Solar System. The dwarf planet is about 3.6 billion miles away from the sun, silently revolving on its orbit for all these years, with no one to talk to and with no visitors to entertain. Yes, little Pluto was once a part of our solar family- etched in all those planetariums, printed on science books of the first graders. However, all this limelight was only short lived. In less than 80 years of its official designation as a planet, the title was taken away.
Pluto was discovered as ‘Planet X’ in the year 1930, by an American astronomer, Clyde Tombaugh. Amassing a lot of popularity during the era, Pluto received more than 1000 proposals for its nomenclature, from all over the world. It was finally named as Pluto, after the Greek god of the underworld, upon the suggestion of an eleven-year-old schoolgirl in England. Ever since then, Pluto enjoyed the stardom, though it was always under the scrutiny of the experts with regard to its mass. The initial calculations showed its mass to be equivalent to that of Earth’s. Followed to that, in 1948, it was estimated to be close to Mars’ mass. Finally, it was the discovery of Pluto’s largest moon, Charon, in the year 1978, which unleashed its actual mass which turned out to be barely 0.2% of the Earth’s mass. Pluto was found to be tiny, and the astronomers built their doubts.
One AU= 92,955, 807 miles (149, 597, 871km) which is approximately 8 light-minutes.
*AU (Astronomical Unit) represents the mean distance between the Earth and the Sun.
For the next decade, things remained calm until the outbreak of new and powerful space-based technologies and observatories. The year 1992 marked the discovery of the Kuiper Belt which is a collection of celestial objects extending from the orbit of Neptune out to 55 astronomical units. Not only was Pluto found to be a part of this belt, but it was estimated that there exist another 70,000 icy bodies with the same composition as that of Pluto. In fact, the size of a number of these objects turned out to be close to Pluto. This fuelled the question of Pluto’s status as a planet, which finally exploded in 2005 when Eris, a trans- Neptunium object, was discovered. Eris was substantially more massive than Pluto, a little bigger in size and its orbit was found be of the same size, probably even larger, than Pluto’s orbit.
Amid the controversy, the General Assembly of the International Astronomical Union (IAU) was held on August 24, 2006, which laid the ground rules for a celestial object to be qualified as a planet.
Out of the three conditions, the first one required the object to be in an orbit around the sun.
Condition two stated that the object should have sufficient gravity to pull itself into a spherical, or nearly spherical, shape.
The third one required the object to have ‘cleared the neighborhood’ of its orbit.
Condition one? Check. Condition two? Check. Condition three?…
Unfortunately, Pluto could not meet the third criterion. This condition implies that the object should be gravitationally dominant on its orbit, either consuming or pushing away other objects with its gravity. Unlike the other planets, with its mass barely 0.7 times the mass of other objects on its orbit, Pluto did not qualify the definition of a planet, and it was demoted. However, any planet which meets the other two criteria, but not the third one, is termed as a dwarf planet. And Pluto thus earned the title of a quintessential dwarf planet.
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