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Why Is Pluto Not a Planet

The Story behind Why Is Pluto Not a Planet

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Ever wondered why is Pluto not a planet? After nearly 100 years of being a planet of our solar system, Pluto planet was discarded from the solar system. In August 2006, the International Astronomical Union (IAU) issued that the status of Pluto was downgraded to that of a “dwarf planet.” Curious about what happened with the planet, I researched and found out that Pluto was indeed an interesting planet. Read below to uncover the story behind the dwarf planet.

The Discovery of Pluto

In 1906, Percival Lowell started a far-reaching project in search of a potential ninth planet, which he termed “Planet X.” By 1909, Lowell and Pickering had suggested several possible celestial coordinates for the planet. Lowell and his observatory searched for his death in 1916, but to no avail. However, on 19th March 1920, Lowell’s observatory captured two faint images of the Pluto planet but they were unrecognized for their contribution. Apart from this, there are sixteen more pre-discoveries but the oldest one remains to be made by the Yerkes Observatory on August 20, 1909.

Until the year 1929, the search for Planet X did not resume when the job was then handed over to Clyde Tombaugh. Clyde was asked to systematically image the night sky in pairs of photographs taken two weeks apart. Following that, he had to observe each pair to check if any objects had shifted position. Clyde used a machine called the blink comparator to create a delusion of movement of any objects that had altered. After nearly a year of searching, he discovered a possible moving object, and after the observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory.

How did Pluto get its Name?

Planet X was named on the suggestion of an 11-year-old girl in England. The girl was extremely interested in Roman legends and thought of naming the icy planet after the god of the underworld. Her grandfather conveyed her idea to a member of the UK’s Royal Astronomical Society. The Society then suggested to its American counterparts at Lowell Observatory. The members of the Society ended up agreeing on the name Pluto as the ‘PL’ possibly gave homage to Percival Lowell. The newly discovered planet then went on to be known as the “King of the Kuiper Belt.”

Why is Pluto no longer a Planet?

When the IAU redefined what it means to be a planet, things went downhill for Pluto in 2006. Pluto planet failed on the third account because its orbit overlaps with Neptune. The planet Pluto was considered to be the ninth planet of our solar system. Despite Pluto being smaller in size, it orbits the sun and has a spherical shape. The planet was relegated in 2006 when the International Astronomical Union (IAU) created a new definition for planets and decided Pluto did not fit the bill. Since the declaration, almost everyone has one question in mind: Why is Pluto no longer a planet?

The IAU downgraded Pluto from being a planet because it did not fulfill one out of three to being a planet.  Essentially Pluto meets all the criteria except one—it “has not cleared its neighboring region of other objects.” The IAU stated Pluto to be a dwarf planet. Pluto is smaller than Earth’s Moon and has a heart-shaped glacier that’s the size of Texas and Oklahoma.

The IAU reclassified it as a dwarf planet, also calling it a “Trans-Neptunian Object.” For many space lovers, Pluto’s demotion felt sudden. But in the academic world of astronomy, it was a process that began just decades after the dwarf planet’s discovery.

What is a Dwarf planet?

A “dwarf planet” is defined as a celestial body in direct orbit of the Sun that is massive enough that its shape is controlled by gravitational forces rather than mechanical forces (and is thus ellipsoid in shape), but has not cleared its neighboring region of other objects. The three criteria of the IAU for a full-sized planet are:

  1. It is in orbit around the Sun.
  2. They has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
  3. It has “cleared the neighborhood” around its orbit.

Pluto meets only two of these criteria, losing out on the third. In all the billions of years it has lived there, it has not managed to clear its neighborhood. You may wonder what that means, “not clearing its neighboring region of other objects?” This means that the planet has become gravitationally dominant and there are no other bodies of comparable size other than its satellites.

Thus, any large body that does not meet these criteria is thereby classified as a “dwarf planet,” and that includes Pluto.

Get your mind-blown by the below-mentioned facts about Pluto:

  • Pluto is the largest dwarf planet.
  • Pluto is only about 1,400 miles wide.
  • It is only about half the width of the United States.
  • Pluto planet has five known moons.
  • Pluto is smaller than the number of moons.
  • Pluto’s atmosphere is thin and composed mostly of nitrogen, methane, and carbon monoxide.
  • Pluto is one-third of water.
  • A year on Pluto is 248 Earth years. A day on Pluto lasts 153 hours or about 6 Earth days.
  • The planet has an eccentric and inclined orbit.
  • Pluto has been visited by one spacecraft.

why is pluto not a planet

Also Read: Everything you need to know about human environment interaction

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