Explain why Pluto is no longer considered a planet.

In short (click here for detailed version)

Pluto has not been considered a planet since 2006 because it does not meet the third criterion of the International Astronomical Union: it has not 'cleared' its orbit of other debris. It is now classified as a dwarf planet.

Explain why Pluto is no longer considered a planet.
In detail, for those interested!

Definition of Planets

A planet is a celestial body that orbits the Sun (or another star) and possesses enough mass to have an almost spherical shape due to its own gravity. Additionally, to be considered a planet, this celestial body must have cleared its orbit of other debris. This means it must be dominant in its orbital region, exerting sufficient gravitational force to eject or incorporate objects of comparable size in its immediate vicinity. These criteria distinguish planets from dwarf planets, which, despite their similarities, have not cleared their orbit. The concept of a planet varies according to the types of stellar systems, but these principles are largely accepted for our solar system.

Pluto: History and Context

Discovered in 1930 by American astronomer Clyde Tombaugh, Pluto was initially classified as the ninth planet in the solar system. Its designation as a planet remained largely uncontested for more than seven decades. Located in the Kuiper Belt, a region filled with small icy bodies, Pluto represents a territory that is both fascinating and mysterious for astrologers and astronomers.

Since its discovery, Pluto has intrigued scientists with its unique characteristics. With an elliptical and tilted orbit compared to the other planets, Pluto takes about 248 Earth years to complete a full revolution around the Sun. Moreover, its size is much smaller than that of the other planets — in fact, it is smaller than our Moon!

Initially, Pluto seemed unique in its corner of the cosmos, until recent discoveries revealed the existence of many similar objects in the Kuiper Belt. This accumulation of Pluto-like objects, notably Eris, another large asteroid, sparked a debate within the scientific community. These discoveries prompted astronomers to reexamine what defines a planet.

Classification Criteria for Planets

In 2006, the International Astronomical Union (IAU) established three criteria for a celestial object to be officially recognized as a planet in our solar system.

1. Orbit around the Sun: The object must revolve around our star. This is a basic but insufficient criterion, as there are many objects that orbit the Sun, from asteroids to comets.

2. Sufficient mass to have a spherical shape: Thanks to its own gravity, the object must be massive enough for its shape to be nearly round. In other words, the object must achieve hydrostatic equilibrium. This excludes many smaller and irregular bodies in the solar system.

3. Ability to "clear" its orbit: The object must gravitationally dominate its spatial neighborhood, meaning it must have eliminated or incorporated all debris and comparably sized objects in its orbit. This is the most complex and decisive criterion. An object that cannot clear its orbital zone is not considered a planet.

These three criteria established a clear framework for distinguishing planets from other celestial bodies, such as dwarf planets and small Solar System bodies. It is precisely the third criterion that led the IAU to reclassify Pluto as a dwarf planet. Pluto shares its orbit with other objects in the Kuiper Belt and has not "cleared" its orbital environment.

Decision of the IAU in 2006

In 2006, the International Astronomical Union (IAU) redefined what constitutes a planet. This decision was based on new discoveries and a better understanding of the solar system. For a celestial body to be considered a planet, it must meet three specific criteria.

First, it must be in orbit around the Sun. Second, it must be massive enough to be in hydrostatic equilibrium, meaning it has an almost round shape. Third, it must have cleared its orbital neighborhood, meaning its gravity imposes its dominant influence in its orbit by ejecting or incorporating any other object of comparable size.

Pluto, despite its previous status as the ninth planet, does not satisfy the third criterion. Although it orbits the Sun and is large enough to be almost spherical, Pluto shares its orbit with other objects in the Kuiper Belt, a region full of small icy bodies. Consequently, the IAU reclassified Pluto as a dwarf planet. This change received extensive media coverage and generated much debate among scientists and the general public.

Scientific and Cultural Implications of the Redefinition

The redefinition of Pluto as a dwarf planet by the International Astronomical Union (IAU) in 2006 has led to significant implications both scientifically and culturally.

From a scientific standpoint, the redefinition required a reevaluation of our understanding of celestial objects in our solar system. For astronomers, the classification as a dwarf planet allowed for better organization and comprehension of the many similar objects found in the Kuiper Belt, a region of the solar system beyond Neptune. This also encouraged more detailed exploration of these regions, expanding our knowledge of the diversity and evolution of celestial bodies. By revisiting the criteria for planets, scientists have refined their definitions and increased the precision of their studies.

From a cultural standpoint, Pluto has always held a special place in the popular imagination. Its demotion sparked strong emotional reactions, ranging from disappointment to humor, and sparked numerous debates among the general public and educators. Children's books, films, and even awareness campaigns have been created to explain this change. This decision also highlighted the importance of science and the evolution of our knowledge, illustrating how discoveries and reclassifications can alter our perceptions and collective knowledge.

In summary, although Pluto is no longer considered the ninth planet of our solar system, its reclassification has enriched our understanding of astronomy and sparked passionate discussions about scientific criteria and their impact on our worldview.

Did you know?

Good to know

Frequently Asked Questions (FAQ)

1

What methods do scientists use to study Pluto?

Scientists use telescopes, space missions like New Horizons, as well as computer models to study Pluto and its composition.

2

Could Pluto be reclassified again in the future?

Although it is possible, the reclassification will depend on new scientific discoveries and the evolution of criteria for classifying celestial bodies.

3

How do people react to the reclassification of Pluto?

The reclassification has caused mixed reactions, with some people being attached to the idea of Pluto as the ninth planet and others accepting the scientific definition.

4

What impact has the redefinition of Pluto had on astronomy?

The redefinition sparked debates within the scientific community and recalibrated our understanding of the diversity of celestial bodies in the solar system.

5

What are the criteria set by the International Astronomical Union to define a planet?

According to the IAU, an object must meet three criteria: orbit around the Sun, have a spherical shape, and have cleared its orbit to be considered a planet.

6

Which other dwarf planets exist in our solar system?

Besides Pluto, other recognized dwarf planets include Eris, Haumea, Makemake, and Ceres.

7

What distinguishes a planet from a dwarf planet?

The main distinctions lie in a planet's ability to orbit a star, to have enough mass for its gravity to give it a spherical shape, and to have 'cleared' its orbit of other debris.

8

Why was Pluto reclassified as a dwarf planet?

Pluto was reclassified as a dwarf planet in 2006 by the International Astronomical Union due to its size and its inability to "clear" its orbit of other objects.

Natural Sciences : Astronomy

No one has answered this quiz yet, be the first!' :-)

Quizz

Question 1/8