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.
Pluto was discovered in 1930 by American astronomer Clyde Tombaugh. At the time, it was the ninth planet, right after Neptune, at the edge of the Solar System. Small, icy, and distant from the Sun, it quickly found its place in popular culture as the last planet of the solar system. For decades, everyone considered it a full-fledged planet, even though it already seemed a bit different from the others, especially due to its size and its particularly inclined and elliptical orbit. Its discovery had initially responded to the search for a mysterious "Planet X", supposed to influence Neptune's orbit, but it ultimately turned out that Pluto was far too small to produce that effect.
In 2006, the International Astronomical Union (IAU) established three specific criteria to distinguish a planet. First, the object must orbit around the Sun. Next, it must have enough mass to assume a roughly round shape due to its own gravity (this is called hydrostatic equilibrium). Last but not least, the planet must have "cleared" its orbital neighborhood, in other words, become the dominant object in its zone without being disturbed by many other celestial bodies sharing its orbit. It is this third point, quite tricky, that changed the game for Pluto.
In August 2006, the International Astronomical Union (IAU), the recognized authority for naming and defining celestial objects, met in Prague to finally settle the question: Is Pluto a true planet or not? After lively discussions among astronomers, they established three clear criteria for being a planet: orbiting the Sun, having a nearly round shape, and most importantly, having "cleared the neighborhood" around its orbit. The result: Pluto meets the first two criteria but fails the last test miserably. Its orbit is located in an area full of other similar objects, the famous Kuiper Belt, which it has never really "cleared." Thus, Pluto lost its official status as a planet to become a dwarf planet, a new term created on this occasion to designate these celestial objects that are halfway between classic planets and small solar bodies.
Pluto is no longer considered a planet in the strict sense because it does not meet one of the three criteria set in 2006 by the International Astronomical Union. It does orbit the Sun and has a nearly round shape due to its own gravity, no problem there. However, Pluto has not managed to clear its orbit: it has not eliminated or absorbed all the space objects that wander near it. Its region is full of comparable celestial bodies, grouped in what is called the Kuiper Belt. Because of this, Pluto is now classified as a dwarf planet, along with other small companions like Eris and Haumea.
The reclassification of Pluto has triggered strong reactions all over the world, and not just among astronomers. Many people have expressed their sentimental attachment to Pluto with humorous slogans like "Pluto, we still love you!" or ironic campaigns: "Give us back the ninth planet!" Petitions have even circulated to defend the poor little celestial body, proving its unique status in popular imagination. TV series and cartoons like The Simpsons have gently mocked this downgrade, showing how much this scientific decision has impacted minds far beyond academic circles.
The dwarf planet Pluto has five known moons: Charon, Styx, Nix, Kerberos, and Hydra. Surprisingly, Pluto and its largest moon Charon orbit around each other, forming a type of double planet known as a 'binary system.'
Pluto takes about 248 Earth years to complete one full revolution around the Sun. Since its discovery in 1930, Pluto has not yet completed a single full orbit around the Sun.
Even though Pluto is no longer classified as a planet, it remains the largest known object in the Kuiper Belt, a vast region of icy objects at the edge of our solar system.
Some other dwarf planets, such as Eris, discovered in 2005, have been at the center of the astronomical debate that led to Pluto's reclassification in 2006. Eris is even slightly more massive than Pluto.
This remains unlikely in the immediate future. The International Astronomical Union (IAU) would need to change its current criteria defining the status of a planet. To do this, it would be necessary to adopt new parameters or to reconsider the current interpretation of the "clearing the neighborhood" criterion.
Sure! Here’s the translation: "Yes! Pluto is now classified as a dwarf planet, a category that includes other similar objects such as Eris, Haumea, Makemake, and Ceres. These bodies orbit the Sun, are spherical due to their own gravity, but do not fully meet the orbital clearing criteria required to be classified as major planets."
The main argument concerns the new criterion introduced by the IAU in 2006, according to which a planet must have cleared its orbital neighborhood. Pluto shares its orbit with several other trans-Neptunian objects and therefore does not meet this condition.
Yes, this reclassification has encouraged astronomers to study the Kuiper Belt and trans-Neptunian objects similar to Pluto more precisely. It has refined our understanding of the composition, origin, and dynamics of this distant part of the solar system.
The decision of the IAU sparked passionate debates. While many supported this decision based on specific scientific criteria, some astronomers and institutions expressed their disagreement and nostalgia regarding Pluto's traditional status. This debate is also reflected in the cultural and media reactions of society, thus creating an increased interest in astronomy.
No one has answered this quiz yet, be the first!' :-)
Question 1/8
