Although it sounds strange, the reality is that until very recently, in 2006, an official classification of the celestial bodies of the solar system had not been developed. This definition from the International Astronomical Union (IAU) set the criteria that we still use today to say what is a planet and what is not. It was precisely with this classification that Pluto was demoted in category and was no longer considered a planet. But is Pluto a planet?
What is considered a planet
The solar system, with its stars and planets, has not always been there. In the beginning, our system was nothing more than a cloud made up of dust and gas. Gravity was what caused these materials to gather in a center from which the Sun was created.
The rest of the particles that remained around were colliding with each other, accumulating at different points and creating a gravity strong enough to accumulate more gas and materials. This is how the planets that orbit the Sun, including Earth, were formed.
For centuries, humans have wondered what those celestial bodies that are above us are. After many studies and discussions, in 2006 the definition of the planet was agreed. So what is considered a planet ? Well, a planet is a celestial body that must meet the following characteristics:
- It needs to orbit the Sun.
- It has to be large enough so that the force of its gravity gives it a spherical shape.
- It has to be large enough that the force of its gravity clears objects of similar size orbiting close to it.
There are several characteristics that differ between Pluto and the planets of the Solar System: Mercury, Venus, Earth, Jupiter, Mars, Neptune, Uranus, and Saturn. However, there is a key difference that caused the year 2006 Pluto to see its status degraded and to stop considering itself as a planet.
Unlike the rest of the planets, Pluto has a large group of celestial objects similar to it around it . This is a similar situation to Ceres, the largest object in the asteroid belt between Jupiter and Mars. Pluto also has a lot of objects that orbit closely, something that invalidates it as a planet .
As we have already explained previously, one of the basic characteristics that a planet must meet is to be large enough for the force of its gravity to clear objects orbiting close to it. For its part, Pluto is unable to do so, so it cannot belong to the same class as the other planets. Pluto does not meet the third of the criteria established by the IAU for a celestial body to be considered a planet, that is, it does not have enough size and gravity to clear its orbit.
Pluto is a planet: yes or no?
Once this is explained, it can be said that this decision was not without controversy and, to this day, there is still discussion in certain circles of astronomers . Precisely, that Pluto becomes a planet again is the objective of a study by Philip Metzger, from the Central University of Florida.
As we have already explained throughout this article, in 2006 the IAU established what the rules were to define what is and what is not considered a planet . Previously, we have already specified what its characteristics should be, and what is the one that Pluto does not meet. So what problem do these scientists see that Pluto is not considered a planet?
Well, the reason why this group of scientists do not believe that the decision is correct is that this characteristic – which Pluto does not fulfill – is arbitrary and does not really matter much. On the other hand, it obviates a characteristic that they do consider basic, such as the training process . At this point, Metzger considers the basic point to be whether it is large enough to be spherical in shape.
The IAU has ruled on these opinions saying that what must be done is to propose a resolution for it to be debated, however, to date no resolution has been proposed. Thus, beyond the opinions that may exist within -and surroundings- of the scientific community, Pluto is not considered a plant .
What is Pluto now
But if Pluto is no longer a planet, what is Pluto now? In its 2006 resolution, the UAI not only established the characteristics to know what a planet was, but also established other groups of celestial bodies. In the case of Pluto, it became a dwarf planet , whose characteristics are:
- It orbits around the Sun.
- It has enough mass so that its shape is spherical or almost spherical.
- It is not a satellite.
- It has not cleared its orbit.
So Pluto is now a dwarf planet . In addition to planets and dwarf planets, another category for objects that orbit the Sun that are neither planets nor dwarf planets are the small bodies of the solar system.