Why Pluto should be reclassified as a planet

Why Pluto should be reclassified as a planet

Researchers at the University of Central Florida in Orlando, US, have suggested that Pluto should be reclassified as a planet after finding that the loss of its planet status was not valid.

The new research says that Pluto should be reclassified as a planet due to finding that the current definition of planets is erroneous.

The etymology of the word planet is the Greek word meaning ‘wanderer’. The International Astronomical Union (IAU) is responsible for the official definition of planets and dwarf planets and, in 2006, the IAU took a vote from astronomers at the IAU General Assembly in Prague, Czech Republic, and reached a consensus on an updated definition of a planet which is still in place today. According to the IAU, the definition of a planet is: “A celestial body that

  • is in orbit around the Sun,
  • has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
  • has cleared the neighbourhood around its orbit.”

Therefore, the Solar System officially consists of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto is classified as a dwarf planet, and a prototype of a new class of Trans-Neptunian objects, rather than a planet.

Pluto is not considered a planet because it shares its orbit with frozen gases and objects in the Kuiper Belt, and Neptune’s gravity influences it.

Why did Pluto lose its planet status?

The decision to exclude Pluto from the planets has been the subject of much controversy among scientists. Kirby Runyon, a scientist at Johns Hopkins University, Baltimore, US, and the new study’s co-author has previously said THAT “[Pluto] has everything going on on its surface that you associate with a planet … There’s nothing non-planet about it.”

Runyon has also previously argued in a short paper this year that a planet should be defined by the intrinsic qualities of the body itself, rather than external factors such as its orbit or other neighbouring objects.

Now the Florida Space Institute, which is part of the University of Central Florida, has published a paper in the journal Icarus, which finds that the current definition of planets is not supported by research. The author of the research paper, Philip Metzger, has reviewed the scientific literature and has identified a fundamental problem with the IAU definition of planets, which relies on the fact that a cleared orbit is the standard for distinguishing between asteroids and planets. However, Metzger says: “They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.” Runyon added: “We showed that this is a false historical claim … it is therefore fallacious to apply the same reasoning to Pluto.”

The argument for why Pluto should be reclassified as a planet also includes the complexity of Pluto as an interesting part of our solar system. Metzger commented: “The only planet that has more complex geology [than Pluto] is the Earth.”

Pluto is a dynamic body, which has an underground ocean, a multilayer atmosphere, organic compounds, and evidence of ancient lakes as well as multiple moons. Metzger argues that scientists already find it functionally useful to define Pluto as a planet in their research papers, despite this being contrary to the official IAU definition of planets.

What would be the ideal definition of a planet?

Alongside the argument that Pluto should be reclassified as a planet, Metzger has suggested that the classification of a planet should be based on whether it is large enough for its gravity to allow it to become spherical in shape. Metzger added: “Dynamics are not constant, they are constantly changing … So, they are not the fundamental description of a body, they are just the occupation of a body at a current era.”

This supports the assertion that a planet should be defined by the intrinsic qualities of a body, rather than by external factors.


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