Not so long ago, Pluto was excluded from the list of planets in the solar system and classified as a dwarf planet. Let's see why Pluto is not a planet.
1. History, or everything is fine
Pluto was first discovered in 1930 by Clyde Tombaugh at the Lowell Observatory in Arizona. Astronomers had long predicted that there was a ninth planet in the solar system, which they called Planet X. Tombo was given the laborious task of comparing many photographic plates with images of areas of the sky taken at intervals of two weeks. Any moving object, such as an asteroid, comet or planet, had to change its position in different photographs.
After a year of observations, Tombaugh finally found an object with a suitable orbit and claimed that he had finally found Planet X. Since the discovery was made at the Lowell Observatory, the observatory team got the right to give the planet a name. The choice was made in favor of the name Pluto, which was suggested by an 11-year-old schoolgirl from Oxford, England (after the Roman god of the underworld).
Astronomers could not determine the mass of Pluto until the discovery of its largest moon, Charon, in 1978. Then, having determined the mass of Pluto (0.0021 Earth masses), they were able to more accurately estimate its size. According to the latest data, the diameter of Pluto is 2400 km. Pluto is just tiny, but then it was believed that there was nothing bigger than this dwarf planet beyond the orbit of Neptune.
2. Something went wrong, or the root of the problem
However, over the past few decades, new powerful ground and space observatories have completely changed the previous ideas about outer areas solar system. Instead of being the only planet in its region, like all the other planets in the solar system, Pluto and its moons are now known to be an example of a large number of objects, united under the name of the Kuiper belt. This region extends from the orbit of Neptune to a distance of 55 astronomical units (the boundary of the belt is 55 times farther from the Sun than the Earth).
According to recent estimates, there are at least 70,000 icy objects in the Kuiper belt that are 100 km or more in diameter and have the same composition as Pluto. According to the new rules for identifying planets, the fact that Pluto's orbit is inhabited by such objects is the main reason why Pluto is not a planet. Pluto is just one of many Kuiper belt objects.
That's the whole problem. Since the discovery of Pluto, astronomers have been discovering larger and larger objects in the Kuiper Belt. The dwarf planet 2005 FY9 (Makemake), discovered by Caltech astronomer Mike Brown and his team, is only slightly smaller than Pluto. Later, several other similar objects were discovered (for example, 2003 EL61 Haumea, Sedna, Orc, etc.).
Astronomers have realized that the discovery of an object larger than Pluto in the Kuiper Belt is only a matter of time.
And in 2005, Mike Brown and his team broke the astonishing news. They found an object beyond the orbit of Pluto that was probably the same size, maybe even larger. Officially named 2003 UB313, the facility was later renamed Eridu. Astronomers later determined that Eris had a diameter of about 2600 km, plus it had a mass about 25% greater than that of Pluto.
With Eris, more massive than Pluto, made up of the same mixture of ice and rock, astronomers have been forced to rethink the concept that the solar system has nine planets. What is Eris - a planet or a Kuiper belt object? What is Pluto? The final decision was to be taken at the XXVI General Assembly of the International Astronomical Union, which was held from 14 to 25 August 2006 in Prague, Czech Republic.
3. Pluto is no longer a planet, or a difficult decision
The astronomers of the association were given the opportunity to vote for various options for determining the planet. One of these options would increase the number of planets to 12: Pluto would continue to be considered a planet, Eris and even Ceres, which was previously considered as the largest asteroid, would be added to the number of planets. Various proposals supported the idea of 9 planets, and one of the options for determining the planet led to the deletion of Pluto from the list of the planetary club. But then how to classify Pluto? Do not consider it an asteroid.
What is a planet according to the new definition? Is Pluto a planet? Does it pass the classification? For a solar system object to be considered a planet, it must meet four requirements defined by the IAU:
The object must orbit the Sun - And Pluto passes.
It has to be massive enough to be spherical by its force of gravity - And here Pluto seems to be all right.
It must not be a satellite of another object. Pluto itself has 5 moons.
It should be able to clear the space around its orbit from other objects - Aha! This rule breaks Pluto, it is the main reason why Pluto is not a planet.
What does it mean to "clear the space around your orbit from other objects"? At a time when the planet is just being formed, it becomes the dominant gravitational body in a given orbit. When it interacts with other, smaller objects, it either absorbs them or pushes them away with its gravity. Pluto is only 0.07 of the mass of all objects in its orbit. Compare with the Earth - its mass is 1.7 million times the mass of all other objects in its orbit combined.
Any object that does not meet the fourth criterion is considered a dwarf planet. Therefore, Pluto is a dwarf planet.
In the solar system, there are a lot of objects with similar sizes and masses that move in approximately the same orbit. And until Pluto collides with them and takes their mass to its hands, it will remain a dwarf planet. It's the same with Eris...
And his orbit is not a circle, but an ellipse, and he himself is very small, so he cannot be on the same list with such as the Earth and with such giants as p.
“It has a different density and small dimensions. It cannot be attributed either to the terrestrial planets or to the giant planets, and it is not a satellite of the planets,” explains Vladislav Shevchenko, professor at Lomonosov Moscow State University.
The conference in Prague left on star charts only eight planets, instead of the usual nine. Since 1930, when Pluto was discovered, astronomers have found at least three more objects in space that are comparable to it in size and mass - Charon, Ceres and Xena. Pluto is six times smaller than the Earth, Charon, its satellite, is ten times smaller. And Xena is bigger than Pluto. Maybe it's all the planets? Yes, and the Moon was then offended by the name "satellite" undeservedly. None of the contenders for planetary status could compare with its dimensions.
“If we say that Pluto is a planet, then we must include not one, but already at first several planets in this class. And then it should consist not of nine planets, but of 12, and a little later - 20- 30 or even hundreds of planets. Therefore, the decision is correct, both culturally correct and physically correct," says Andrey Finkelstein, director of the Institute of Applied Astronomy Russian Academy Sciences.
But astrophysicists protest. If we classify objects by size and type of orbit, then any shapeless, but very large cosmic body, What revolves around the sun, also a contender for the title of the planet. A planet, astronomers' opponents say, is a sphere created by gravity.
“It’s just that the size doesn’t mean anything. If the body is loose, then even a small one can only be supported by gravity and will have round shapes. That is, a small body can be a planet,” explains Vladimir Lipunov, astrophysicist, professor at Moscow State University named after M.V. Lomonosov. The results of this conference put an end to a long-standing dispute
astronomers and answered the question why Pluto is not a planet in the solar system.Pluto has always been the least explored planet. The only one where the atmosphere appears only for a while, when the cosmic body approaches the Sun - the ice melts from the heat. But they again tighten Pluto as soon as it moves away from the star.
Now the American scientists are in frustration. Not only does the US own the discovery of 1930, but the status of the greatest expedition of the already sent New Horizons probe is in jeopardy. In nine years, the Earth was supposed to see pictures of the planet farthest from us, and would receive only a photo of the asteroid.
So, by the will of the earth, the most mysterious planet of the solar system has been crossed out from the lists. Pluto is beautiful, it is a very regular ball, reflecting sunlight several hundred times brighter than the moon. In motion, he is sedateness itself: one year on Pluto is 248 of ours. Finally, the "planet" Pluto is so far from the Sun that the celestial body from its orbit is only a point. Hence the cold - minus 223 degrees Celsius. Enough reasons to be mysterious! Not even a hundred years have passed since the discovery of the planet. (Hence, in the ancient astrological forecasts Pluto was not taken into account.) Yes, and having opened it, they did not immediately figure out what it was. At first it was believed that it was much larger than now proved, and in textbooks it is called the ninth planet, although it moves in its orbit in such a way that sometimes it turns out to be the eighth planet from the sun! And for a long time it was considered a double planet, until it was found out that Charon, its satellite, has no atmosphere.
But controversy over former planet Pluto led to the adoption (this is 400 years after Galileo pointed the first telescope at the stars) the following definition: only celestial bodies that revolve around the Sun, have enough gravity to have a shape close to a sphere and occupy their orbit alone are considered planets .
But there is no cause for concern, since nothing has changed. Pluto, at least, remains in its original place. We answered the main question: "Why Pluto is not a planet."
The existence of Pluto was first discovered at the Lovell Observatory in Flagstaff, Arizona. Astronomers had long predicted the existence of a distant ninth planet in the solar system, which they called among themselves Planet X. The discovery of the planet Pluto Twenty-two-year-old Tombo was given the laborious task of comparing photographic plates.
The task was to compare two images of a section of outer space taken with a difference of two weeks. Any object moving in space, like an asteroid, comet or planet, would have to have a different location in the images. After a year of observations, Tombo finally managed to locate an object in the correct orbit and realized that he had discovered Planet X.
Since the celestial body was discovered by Lovell's team, the team was given the right to assign a name to it. It was decided to give the celestial body the name Pluto. The name was proposed by an eleven-year-old schoolgirl from Oxford (in honor of the Roman god - the guardian of the underworld). From that moment on, the solar system had 9 planets.
Before discovery in 1978 largest moon Pluto Sharon, astronomers could not accurately determine the mass of the planet. Knowing its mass (0.0021 Earth), scientists were able to more accurately determine the size of the object. At the moment, the most accurate calculations indicate that Pluto is 2,400 km in diameter. This is a very small value, for example: Mercury has a diameter of 4.880 km. Although Pluto is tiny, it is considered the largest celestial body beyond the orbit of Neptune.
Why was Pluto excluded?
In the past few decades, new ground-based and space-based observatories have begun to change previous ideas about the outer solar system. In contrast to the old assumption that Pluto was a planet like the others in the solar system, it was now believed that Pluto and its moons were a case of a large cluster of objects known as the Kuiper Belt.
This location extends from the orbit of Neptune by about 55 astronomical units (55 distances from the earth to the Sun). Authoritative astronomers estimate that there are at least 70,000 icy objects in the Kuiper Belt, with the same composition as Pluto, reaching a size of 100 kilometers or more.
According to the new terminology, Pluto was no longer a planet, but simply one of many Kuiper Belt objects.
How did Pluto stop being a planet?
The problem was that astronomers were able to discover larger and larger objects in the Kuiper Belt. FY9, discovered by Caltech astronomer Brown Mike and his team, was only slightly smaller than Pluto. There were also several other objects in the Kuiper Belt with the same classification.
Astronomers realized that the discovery of an object in the Kuiper Belt, more massive than Pluto, was only a matter of time. Finally, in 2005, Brown Mike and his team caused the effect of a “bombshell”. They managed to discover a celestial body located beyond the orbit of Pluto, which has the same, and maybe a larger size. Named UB13 since 2003, it was later named Eris. Since its discovery, scientists have been able to calculate its size - 2,600 km. It also has a mass 25% greater than that of Pluto.
Since Eris was larger, had the same ice-stony composition and was more massive than Pluto, the assumption that there are 9 planets in the solar system began to completely fall apart. The astronomers decided that they would make the final decision on the status of the planet at the XXVIth General Assembly of the Congress of the International Astronomical Union, which was held from 14 to 25 August 2006 in Prague, the capital of the Czech Republic.
IAU General Assembly
What was Eris, a palnet or a Kuiper Belt object; for that matter, what was Pluto (or was Pluto a planet)?
Astronomers were given an opportunity to review and determine the status of the planets. One of the proposals under consideration was: increasing the number of planets to 12. At the same time, Pluto remained a planet, and Eris and Ceres, which had previously had the status of giant asteroids, were equated to the status of planets. An alternative proposal suggested: leave the number of planets at nine, without any scientific justification. The meaning of the third proposal was to reduce the number of planets to eight, with the release of Pluto from among the planets. What was decided?.. In the end, the vote was controversial decision, about the downgrading of Pluto (and Eris) to the status of a "dwarf planet", according to the newly created classification.
What was decided? Is Pluto a planet? Or is it an asteroid? For an asteroid to be considered a planet, it must meet these three requirements defined by the IAU:
- it must orbit around the Sun - YES, so Pluto can be a planet.
“It must have enough gravity to form a ball on its own,” Pluto agrees.
- It must have a "cleaned orbit" - what is it. Here's where Pluto doesn't follow the rules and isn't a planet.
What is Pluto anyway?
What does “cleaned orbit” mean, why is Pluto not a planet? When planets form, they become the predominant gravitational object in their orbit in the solar system. When interacting with other, smaller objects, they either absorb or tie them into orbit with their gravitational force. In Pluto, there are only 0.07 masses of all objects in the vicinity of its orbit. In turn, the Earth, 1.7 million times the mass of all objects in the vicinity of its orbit, respectively.
Any object that does not meet at least one condition is considered a dwarf planet. Therefore, Pluto is a dwarf planet. There are many objects of various masses and sizes in the immediate vicinity of its orbit. And until Pluto collides with many of them and takes their mass, it will retain its status as a dwarf planet. Eris has a similar problem.
It's not hard to imagine a future in which astronomers can detect in the far reaches of solar system an object large enough to qualify as a planet. Then our solar system will again have nine planets.
Even though Pluto is no longer officially a planet, it is still of great interest for research. This is the reason NASA launched their spaceship New Horizons to explore Pluto. New Horizons will reach the planet's orbit in July 2015 and take the first close-up pictures of the dwarf planet.
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Why is Pluto not considered a planet?: discovery of Pluto with photo, finding objects in the Kuiper belt, new IAU classification and criteria, dwarf planet.
In 1930, Clyde Tomb managed to find Pluto, which became the 9th planet of our system. The scientist photographed the sky for a whole year and studied the pictures. On one pair, he noticed a shifting object. The name came from an 11-year-old schoolgirl in honor of the Roman deity who rules the other world.
Why Pluto is no longer a planet
Little was known about the mass until the discovery of a large satellite of Charon nearby (1978). As a result, we managed to come to the size (2400 km). Despite its tinyness, it was considered the last object and planet beyond the orbit of Neptune.
But terrestrial instruments improved, we managed to launch devices into space, and we were able to expand the boundaries of observation. Soon they found the rest of the moons of Pluto, and then the Kuiper belt, distant from Neptune at 55 AU.
At least 70,000 icy bodies live in this area, which are the same as Pluto in composition and extend 100 km or more in width. With their discovery, new rules appeared and Pluto did not pass the test for planetary nature.
The problem is the following. Each time there were more and more objects that exceeded the parameters of Pluto.
And in 2005, Michael Brown finds Eris, located further, but larger than Pluto (2600 km) and larger in mass. The concept of 9 planets started to crumble. What is Eris? Also a planet or just an object from the Kuiper belt? And then what is Pluto? A dispute ensued between scientists, and in 2006 a meeting of the IAU was convened in Prague.
It was important to derive a clear definition of the concept of "planet". If they voted for one version, then the number solar planets increased to 12, but as a result, we reduced it to 8. What is Pluto?
Now it is a class of dwarf planets.
To become a planet, the body must:
- make revolutions around the sun;
- have sufficient massiveness to become spherical;
- clear the surroundings of objects;
Pluto failed to fulfill the last condition. Now all bodies that meet the first two but fail on the third requirement are called dwarf planets.
But let's not forget that large objects are hidden in the Kuiper belt and one of them can become the 9th planet. With the downgrade, Pluto has not lost its popularity and scientific interest. Therefore, in 2015, the New Horizons mission was sent to him. Let's not forget that there are still scientists who do not recognize the decision of the IAU.
