Pluto's discovery was pure coincidence. The discovery of it was pretty much an accident on the part of Percival Lowell. But what exactly was this mistake, or who is Percival Lowell? Well, I'd better start from the beginning.
After Neptune was discovered in 1846 by a series of conflicting observations, which is another story, Astronomers noticed that, according to their observations, Uranus and Neptune's orbits seemed to shift slightly, which led astronomers to believe that there was another planet further out than Neptune. Over the years, this came to be popularly known as Planet X.
Meanwhile, while this was happening, astronomers had begun to realize that some comets were on periodic orbits that could be predicted to a fairly good accuracy. The most famous was Halley's comet, displaying a huge tail, to the awe of observers around the world, every 75.3 years. After this was found, astronomers began to calculate the orbits of other comets, finding many comets with fairly short periods. However, as they began to calculate the orbits, they noticed that some appeared to take much longer to go around the Sun. People began to wonder where they came from, how they got here from so far away, and why they appeared to- in some cases- be making a single orbit around the Sun before being flung into deep space. In 1950, a man named Jan Oort proposed that the comets came from an area far away from the Solar System, where numerous icy bodies orbited the Sun in very, very slow orbits. Occasionally, gravitational interactions between these bodies would catapult one onto a new orbit. Most of the time, they flew out of the Solar System, but sometimes it send them hurtling on parabolic orbits straight towards the sun. Today, this theoretical cloud of bodies is called the Oort cloud in his honor.
Astronomers thought that Planet X was from the inner Oort cloud, and that it sometimes came on an elliptical orbit to where Uranus and Neptune's orbits were. One of them, named Percival Lowell, was especially determined to find this planet. He spent the last few years of his life making calculations based on the observed discrepancies in the ice giants' orbits, and searched for the planet based on these calculations. Although he, oddly enough, actually did find Pluto in his images, he deemed it too small to be the object he was looking for and went on. Lowell never found the planet he was looking for, but the search for Planet X was not over.
A few decades later, in Burdett, Kansas, Clyde Tombaugh was working on telescopes, aspiring to a career as an Astronomer. He built his own telescopes and used the images from his telescopes to draw maps of Mars and Jupiter. After sending these images of the Lowell Observatory, they recognized his passion and talent, and hired him to look for the long-saught planet.
Tombaugh looked repeatedly in the area predicted by Lowell, searching for any sign of movement. He worked long hours in the observatory, comparing photographic plates. Finally, on February 18th, 1930, Lowell was looking at a couple of plates taken the previous month, and finally found the planet. Astronomers around the world celebrated the new discovery, and quickly began to propose names for it. The final name, however, came from an unlikely place. Venetia Burney, a girl only 11 years old, heard about the planet's discovery, suggested the name Pluto to her mother. After her mother gave the idea to the astronomers at the Lowell observatory, it was soon decided to be chosen because Pluto was the Roman god of the underworld, who had the ability to turn invisible. Plus, the first two letters of it were Percival Lowell's initials.
Pluto had a name, and the search for Planet X was complete, but it didn't end there. Astronomers making further, more detailed observations of Uranus and Neptune noticed that the observed wobbles in their orbits was only a result of bad observations. This meant that the calculations that led to the discovery of Pluto were only a mistake, and Tombaugh was just extremely lucky to find Pluto near the incorrectly predicted spot.
Meanwhile, astronomers made mass estimates of Pluto to see just how large it was, and more observations of it brought the mass from 1 Earth in 1931, to 0.1 Earths in 1948. By 1976, the estimate had dropped to 0.01, or only 1/100th Earth's mass. Meanwhile, other object in the area began to be discovered. In 1977, astronomers found a Centaur, or a frozen comet, called 2060 Chiron. It orbited from 8 to 18 Astronomical units out. While this wasn't as far out as Neptune or Pluto, it was only the second recent discovery of its kind. However, in 1992, (15760) 1992 QB1 was discovered with an orbit taking it from 40 to 47 AU out. this meant that it orbited as far out as Pluto! This led astronomers to question Pluto's special role as a planet, but observations showed the asteroid to be only about 1/9th the size of Pluto. The designation sticked.
This wasn't for long, however. In 2003, astronomer Mike Brown discovered 136199 Eris, which, due to observations, was found to be more massive than Pluto, by about 0.0007 Earths. This may not seem like much, but Pluto's mass was only 0.0028 that of Earth's. This was the only thing astronomers needed to finally demote Pluto's position.
In 2006, the International Astronomical Union decided to revise the classification of what a planet was. First, a planet must orbit around the Sun, not another planet. This means moons can not be planets. Second, a planet must be massive enough to make itself into a sphere. Semispheres like Vesta couldn't be planets even if they did fulfill the final requirement. This was that the object must have enough gravity to clear any objects with a significant mass of it out of its orbital path. While pluto fulfills the first two, it doesn't fulfill the third.
Simultaneously, astronomers created the classification of Dwarf Planet. These bodies have the first two requirements fulfilled, but not the third. Today, there are 6 of these: Ceres, Pluto, Haumea, Makemake, Eris, and Sedna. Many more objects in the Kuiper Belt are suspected dwarf planets.
Despite its current status as Dwarf Planet, Pluto has had arguably one of the most interesting histories of any of the planets in the Solar System, and is more than worthy of this title, if not being an official Planet. But, no matter whether it's classified as a Dwarf Planet, regular one, or anything else around the Sun, it was simply a matter of pure coincidence that lead to the discovery of the (almost) 9th planet...
Do you think Pluto should have been a planet?
After Neptune was discovered in 1846 by a series of conflicting observations, which is another story, Astronomers noticed that, according to their observations, Uranus and Neptune's orbits seemed to shift slightly, which led astronomers to believe that there was another planet further out than Neptune. Over the years, this came to be popularly known as Planet X.
Meanwhile, while this was happening, astronomers had begun to realize that some comets were on periodic orbits that could be predicted to a fairly good accuracy. The most famous was Halley's comet, displaying a huge tail, to the awe of observers around the world, every 75.3 years. After this was found, astronomers began to calculate the orbits of other comets, finding many comets with fairly short periods. However, as they began to calculate the orbits, they noticed that some appeared to take much longer to go around the Sun. People began to wonder where they came from, how they got here from so far away, and why they appeared to- in some cases- be making a single orbit around the Sun before being flung into deep space. In 1950, a man named Jan Oort proposed that the comets came from an area far away from the Solar System, where numerous icy bodies orbited the Sun in very, very slow orbits. Occasionally, gravitational interactions between these bodies would catapult one onto a new orbit. Most of the time, they flew out of the Solar System, but sometimes it send them hurtling on parabolic orbits straight towards the sun. Today, this theoretical cloud of bodies is called the Oort cloud in his honor.
Astronomers thought that Planet X was from the inner Oort cloud, and that it sometimes came on an elliptical orbit to where Uranus and Neptune's orbits were. One of them, named Percival Lowell, was especially determined to find this planet. He spent the last few years of his life making calculations based on the observed discrepancies in the ice giants' orbits, and searched for the planet based on these calculations. Although he, oddly enough, actually did find Pluto in his images, he deemed it too small to be the object he was looking for and went on. Lowell never found the planet he was looking for, but the search for Planet X was not over.
A few decades later, in Burdett, Kansas, Clyde Tombaugh was working on telescopes, aspiring to a career as an Astronomer. He built his own telescopes and used the images from his telescopes to draw maps of Mars and Jupiter. After sending these images of the Lowell Observatory, they recognized his passion and talent, and hired him to look for the long-saught planet.
Tombaugh looked repeatedly in the area predicted by Lowell, searching for any sign of movement. He worked long hours in the observatory, comparing photographic plates. Finally, on February 18th, 1930, Lowell was looking at a couple of plates taken the previous month, and finally found the planet. Astronomers around the world celebrated the new discovery, and quickly began to propose names for it. The final name, however, came from an unlikely place. Venetia Burney, a girl only 11 years old, heard about the planet's discovery, suggested the name Pluto to her mother. After her mother gave the idea to the astronomers at the Lowell observatory, it was soon decided to be chosen because Pluto was the Roman god of the underworld, who had the ability to turn invisible. Plus, the first two letters of it were Percival Lowell's initials.
Pluto had a name, and the search for Planet X was complete, but it didn't end there. Astronomers making further, more detailed observations of Uranus and Neptune noticed that the observed wobbles in their orbits was only a result of bad observations. This meant that the calculations that led to the discovery of Pluto were only a mistake, and Tombaugh was just extremely lucky to find Pluto near the incorrectly predicted spot.
Meanwhile, astronomers made mass estimates of Pluto to see just how large it was, and more observations of it brought the mass from 1 Earth in 1931, to 0.1 Earths in 1948. By 1976, the estimate had dropped to 0.01, or only 1/100th Earth's mass. Meanwhile, other object in the area began to be discovered. In 1977, astronomers found a Centaur, or a frozen comet, called 2060 Chiron. It orbited from 8 to 18 Astronomical units out. While this wasn't as far out as Neptune or Pluto, it was only the second recent discovery of its kind. However, in 1992, (15760) 1992 QB1 was discovered with an orbit taking it from 40 to 47 AU out. this meant that it orbited as far out as Pluto! This led astronomers to question Pluto's special role as a planet, but observations showed the asteroid to be only about 1/9th the size of Pluto. The designation sticked.
This wasn't for long, however. In 2003, astronomer Mike Brown discovered 136199 Eris, which, due to observations, was found to be more massive than Pluto, by about 0.0007 Earths. This may not seem like much, but Pluto's mass was only 0.0028 that of Earth's. This was the only thing astronomers needed to finally demote Pluto's position.
In 2006, the International Astronomical Union decided to revise the classification of what a planet was. First, a planet must orbit around the Sun, not another planet. This means moons can not be planets. Second, a planet must be massive enough to make itself into a sphere. Semispheres like Vesta couldn't be planets even if they did fulfill the final requirement. This was that the object must have enough gravity to clear any objects with a significant mass of it out of its orbital path. While pluto fulfills the first two, it doesn't fulfill the third.
Simultaneously, astronomers created the classification of Dwarf Planet. These bodies have the first two requirements fulfilled, but not the third. Today, there are 6 of these: Ceres, Pluto, Haumea, Makemake, Eris, and Sedna. Many more objects in the Kuiper Belt are suspected dwarf planets.
Despite its current status as Dwarf Planet, Pluto has had arguably one of the most interesting histories of any of the planets in the Solar System, and is more than worthy of this title, if not being an official Planet. But, no matter whether it's classified as a Dwarf Planet, regular one, or anything else around the Sun, it was simply a matter of pure coincidence that lead to the discovery of the (almost) 9th planet...
Do you think Pluto should have been a planet?
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