On many of our daily astronomical tours, it is common for some people ask whether Pluto is a planet or not? And if it was one, why isn’t it one now? Today in our blog we give you the keys to understanding this… astronomical confusion.
Pluto was discovered in 1930 in the United States and this is precisely one of the first keys to the affair:
#1: Pluto is the only planet in the solar system discovered by the US. Remember that the classical planets, those visible to the naked eye (Mercury, Venus, Mars, Jupiter and Saturn) have been known for centuries and centuries, so it is not possible to attribute their discovery to a particular person. Uranus was discovered by William Herschel in 1971 and Neptune by the German Johann Galle.
From the moment of its discovery Pluto seemed to be a “complicated” planet. It was clear that it was tiny, which broke the original idea that our Solar System was organized in such a way that the small, rocky planets were near the Sun and the gaseous giants were further away. Then Pluto appears, a small rocky body out in the confines of the Solar System.
#2: Pluto broke the acknowledged distribution of the planets in our solar system.
In addition, Pluto did not fulfill the orbital resonance that seems to “order” our Solar System, which causes each planet to be approximately twice the distance from the Sun than the planet before it. To simplify it (a lot) if Mercury is 1 away, Venus is 2 away, Earth 4 away, Mars 8 away … but nevertheless Pluto is not twice the distance from the Sun as Neptune is. In fact, at some points of its orbit, Pluto invades the orbit of Neptune and is positioned closer to the Sun!!
#3: Pluto does not conform to the rules of orbital resonance with the other planets.
One of the biggest problems with Pluto is that it is not on the same orbital plane as the rest of the planets. I.E. while all the planets orbit the Sun on the same plane, Pluto does it with an inclination of up to 16º.
#4: Pluto orbits on a different orbital plane to the other planets.
But without a doubt, the biggest obstacle occurred when we began to study the orbit of this planet and began to discover dozens and even hundreds of objects that shared the same orbit as Pluto, exactly the same orbit. In fact, even some objects of almost the same size, such as Eris, were found. The fifth reason is the most compelling.
# 5: Pluto appears simply to be one more object on an asteroid belt, called the Kuiper belt.
But of course … if we go back to reason # 1, which says that it is the only planet discovered by the US, we can find the reason why, when all these things were discovered and its status as a planet was questioned, the Americans got seriously angry! In the end, it was THEIR planet and they bitterly defended that Pluto should continue to be defined as a planet. The truth is that with very good arguments, in that, to call a body which is so large that it had acquired the spherical shape of a planet, an “asteroid” was not very logical either.
The compromise solution was found in 2006 in Prague, when a meeting of the International Astronomical Union dictated the three requirements for a planet to be considered as such:
- The object must be in orbit around the sun.
- The object must have gravity enough to be round.
- The object must have cleared its neighboring orbit.
The third point is the one that caused Pluto to lose its status of Planet, because it does not meet it. However, to satisfy everyone, it was agreed to propose an intermediate category called “dwarf planet” for those bodies that only meet the first two. That’s why Pluto is our favorite dwarf planet.
At AstroAndalus , your agency specializing in astronomical tourism, we do not often observe the planet Pluto, as it is extremely difficult to see, but if we have lots of fun observing its big brothers like Júpiter and Saturno.
We are looking forward to meeting you on one of our activities! Information and reservations at www.astroandalus.com/en