Why isn’t pluto a planet anymore: Reason for removing Pluto from the list of planets after 70 years

Why isn’t pluto a planet anymore: Reason for removing Pluto from the list of planets after 70 years

All the controversy ended and all the wars and quarrels between astronomers over whether or not a number of Kuiper belt objects were planets were over. Pluto was removed from the list of planets by a new criterion presented at the meeting of the International Astronomical Society. Pluto is a distant object that has been discovered for more than 70 years, but the fate of this icy world, which until recently was known as the ninth planet in the solar system, removed from the orbit of the planets.

Pluto Facts

Fast Facts

  • Diameter at equator = 1, 457 miles (2,344 km)
  • Average temperature = -380 degrees Fahrenheit (-223 degrees Celsius)
  • Average distance from the Sun = 3675 miles (5914 million kms)
  • Length of year = 248 Earth years
  • Period of rotation = 6 days, nine hours (retrograde)
  • Number of moons = 1
  • Volume of planet compared with Earth = one two-hundredth
  • Minimum traveling time from Earth = Approx 14 years

Distinguishing features

Embroiled in a scientific debate as to whether it should be classified as a planet.


Pluto is the solar system’s smallest and most distant planet and is never visible without the aid of a fairly large telescope. However, it you’re really keen, these directions and move star-to-star you’ll locate Pluto:

Use a star chart to help locate the naked-eye, 2.6-mag Zeta Ophichus star in your telescope finder.

Move the telescope 3.1-degrees east toward the 4.6-mag star at the edge of the finder’s field. That star is labelled “20” on star charts.

You will need to use the main telescope for the final move. You’ll need to know the eyepiece field-of-view — a 1º field is best for these steps. Centred on the 20-Oph star, move the telescope slightly more than 1½º directly south until you centre an 8-mag star.

Now swing the telescope in RA east through a field of ¾º.

If you can accomplish the above, you’ll have Pluto in your sights!

Probing the facts

The Pluto Express will consist of two spacecraft, each taking twelve years to reach Pluto. The goal of the mission is to learn more about Pluto’s atmosphere, surface features and geologic composition.

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Why was Pluto removed as a planet after 70 years?

Pluto was removed from the list of planets in the solar system because it failed to meet one of the three conditions for being a planet. In a meeting of the International Astronomical Society, it was confirmed that a space object would be called a planet if it orbited primarily a star. The second condition states that it must have sufficient mass to achieve hydrostatic equilibrium. The implication of this condition is that only objects with a spherical shape can expect to be a planet.

Read more: How Old is the Universe? (All Calculations so far)

Pluto had the first two conditions, but because it was a member of the Kuiper belt, it could not meet the third condition and was therefore removed from the list of planets in the solar system . In this controversial meeting, the International Astronomical Society not only determined the characteristics of a planet, but also introduced new definitions in order to avoid future problems. In this session, the non-stellar objects of a system were divided into three categories, which are as follows:

  1. Planet: A object that orbits a star, has reached hydrostatic equilibrium, is not in the asteroid belt, and is not orbiting a planet like a moon.
  2. Dwarf planets: A group of objects that are in the asteroid belt has reached hydrostatic equilibrium, that is, they are spherical in shape, and the moon is not considered a dwarf planet.
  3. Objects of the third group: The members of this group include all moons (moons), asteroids, and small and large rocks in the interplanetary space and in general all the small objects of a stellar system.

How Does A Planet Become A Dwarf Planet?

It has to be in orbit around the Sun that is tilted to about 60 degrees, as opposed to the usual 180 degrees for the plane of Earth’s orbit. Dwarf planets are the “missing planets” between the eight planets in our Solar System. How Was Pluto Downgraded? In 2005, the IAU was asked to settle a dispute about whether Pluto was a full planet or a dwarf planet by the International Astronomical Union Working Group for Planetary System Nomenclature (IAU-WGPSN), which was established to settle similar disputes about the classification of astronomical objects. The IAU-WGPSN ruled that Pluto was not a full planet and, therefore, it was renamed as a dwarf planet.

While the IAU downgraded Pluto to “dwarf planet,” it did not downrank it from its status as a planet—and to understand why one must look at the technical criteria the IAU uses to determine what a planet is and what a planet’s orbit is. In order for a celestial body to be considered a planet by the IAU, it must:

  • Be in orbit around the Sun (which is the only “semiclassical” type of orbit in which a planet is defined).
  • Be massive enough to retain an atmosphere (this requires a mean albedo of 0.069, which Pluto currently has)
  • Move across its own plane of rotation, and not perturb the orbit of any other objects
  • Over the course of many years the IAU’s Planetary Science Committee (PSC) recommended dropping Pluto from the list of planets.

Now all the controversy is over and the solar system, which was supposed to have several new planets, became an eight-planet system with the loss of one old planet. The decision of the International Union of Astronomers, which led to the removal of Pluto from the list of planets in the solar system, provoked the anger and reaction of some of the world’s leading astronomers.

According to the BBC: Dr. Allen Stern, NASA senior scientist who is leading the “New Horizons” space mission to Pluto, has said in a strong reaction that this decision is a shame. Mr. Stern, who did not take part in the vote, rejected the new definition of a planet that removed Pluto, saying it was incorrect. He was not present at the polling station.

Read more: What is the structure of the Universe? Geometry of spacetime

On the other hand, voting was not possible electronically and this has caused criticism among astronomers. Dr. Stern, a well-known NASA scientist who launched the New Horizon spacecraft to Pluto, has said that he and some astronomers are seeking a request to return Pluto to the list of planets in the solar system by changing the definition of the planet. The decision of the International Astronomical Union has been ridiculed in some online circles.

The International Union of Astronomers has been the official reference for designations in the world of astronomy since 1919. Of the 2,500 astronomers present at the summit on Thursday, only 424 remain in Prague. Pluto is much farther and smaller than the eight planets in the solar system and orbits the sun on a different plane from the other planets. Experts have long disagreed on whether Pluto deserves the title of planet. Astronomers at the summit described Pluto as a small “ice dwarf” planet.

Read more: Planets – Fast Facts, Distinguishing features, Visibility etc.

The issue of Pluto being removed from the list of planets in the solar system became more acute when another object beyond Pluto and larger, called 2003 UB313, was discovered by an American astronomer. After observing the 2003 UB313 by the Hubble Space Telescope, it was discovered that this celestial body is larger than Pluto and has a diameter of 3,000 kilometers. The new decision of these astronomers will cause many changes in textbooks and encyclopedias. The solar system after these changes includes eight planets, namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.


For some reason, most of the popular astronomy community—and most Americans, in particular—lack a clear and understandable understanding of the planet and dwarf planet systems. By relying on circular definitions and understanding, it is possible to analyze this topic and come to a clear understanding of where Pluto currently resides in the solar system and why it was once considered a planet.

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Why was Pluto removed as a planet

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