Why is Pluto no longer a planet? The sensational decision was made on August 25, 2006 by 2.5 thousand participants of the Congress of the International Astronomical Union. Millions of astronomy students‚ thousands of star charts‚ hundreds of scientific papers will be rewritten. From now on, Pluto will be removed from the list of planets in the solar system. In ten days of debate, the International Astronomical Union has stripped the most mysterious object of the solar system of the status that it had for only 76 years. However, over the past few decades, powerful new ground-based and space-based observatories have completely changed previous ideas about the outer regions of the 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 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. 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 the planet Jupiter. "It has a different density, and the dimensions are small. 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 only eight planets on the star maps instead of the usual nine. Since 1930, when Pluto was discovered, astronomers have found at least three more objects in space 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. Could it be that these are all the planets? Yes, and the Moon was then undeservedly named "satellite". None of the contenders for planetary status could compare with its dimensions. "If we say that Pluto is a planet, then we should attribute to this class not one, but already at first several planets. And then the solar system should not consist of nine planets, but of 12, and a little later - 20 -30 and even hundreds of planets. Therefore, the decision is correct. It is both culturally correct‚ and physically correct," says Andrey Finkelstein, director of the Institute of Applied Astronomy of the Russian Academy of Sciences. In the end, astronomers voted for a rather controversial decision by the standards of that time and attributed Pluto (and other similar objects) to a new class of objects - to the "dwarf planets". What is a planet according to the new definition? Is Pluto a planet? Does it pass the classification? For an object in the solar system to be considered a planet, it must meet four requirements defined by the IAU: 1. The object must orbit the Sun - AND Pluto passes. 2. It has to be massive enough to be spherical with its gravitational force - And here everything seems to be all right with Pluto. 3. It must not be a satellite of another object. Pluto itself has 5 moons. 4. He must be able to clear the space around his 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. The same is true of Eris. But astrophysicists protest. If we classify objects by size and type of orbit, then any shapeless, but very large cosmic body that revolves around the Sun, is also a contender for the name of the planet. Planets‚ say opponents of astronomers‚ is a sphere‚ created by gravity. "Just the size does not mean anything. If the body is loose, then even a small one can be supported only by gravity and will have round shapes. That is, a small body can be a planet," explains Vladimir Lipunov, astrophysicist, professor of Moscow State University named after M.V. Lomonosov. The results of this conference put an end to the long-term dispute of 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, Pluto is so far from the Sun that the celestial body from its orbit is just 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. (Consequently, Pluto was not taken into account in ancient astrological forecasts.) 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 the controversy over 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 sufficient gravity to have a shape close to a sphere and occupy its orbit alone. Although Pluto is now considered a dwarf planet, it is still a fascinating object to explore. And so NASA sent the New Horizons spacecraft to visit Pluto. New Horizons will reach Pluto in July 2015 and will take a close-up photo of Pluto for the first time in human history. Of course, it is worth noting that Nature, in general, does not care how a tiny civilization in one of the billions of star systems classifies the objects of this system. Earth, Mars, Pluto are just clumps of matter revolving around a much more massive body, and Pluto will always be just Pluto, no matter what category of objects we have invented, we refer to it. But there is no cause for concern, since nothing has changed. Pluto, at least, remains in its original place.
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, powerful new ground-based and space-based observatories have completely changed previous ideas about the outer regions of the 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 Pluto seems to be doing just fine here.
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...
Some say with all certainty that all the planets are just clumps of matter revolving around the Sun, having their own indicators: diameter, mass, volume and area. And Pluto is no exception. Judge for yourself:
So why did Pluto, "born", not bother to honor until the very "death" to be a planet? It turns out that in order to be officially called a planet of the solar system, it is necessary that its data and functions meet certain conditions, namely:
- revolved in orbit around the sun;
- so that they take a shape close to a ball under the influence of their own gravitational forces (for this you need to be massive);
- the ability to clear the vicinity of its orbit from other objects by gravity (i.e., when interacting with smaller objects, they must either push them out with their gravity or absorb them).
- should not be satellites of other planets, and should not themselves have one (and the New Horizons spacecraft photographed all five of Pluto's moons).
Why is Pluto not a planet? They "pumped up" the correspondence to the points for clearing the surroundings and the presence of satellites. It is so small that its mass is only 0.07 of all objects, and this is not enough to clear the area from asteroids.
For such planets, scientists introduced a new definition: they began to be called "dwarf". This included Pluto. Another version of why he is so "offended." Astronomers claim that its orbit is very elongated and too inclined with respect to the plane in which the Earth's orbit lies (by 17 °; next comes Mercury ─ a deviation of only 7 °). As for elongation, yes, Pluto's orbit is elongated, but, for example, the same Mercury is elongated in almost the same way.
And the message that NASA managed to open in 2003 added fuel to the fire. the celestial body UB13, called Eris, differs from the declared planet in its large size (2,600 km) and a mass that is 25% higher than its mass. A real "bombshell" effect! Pluto is not a planet (yet!), as there is talk of returning this status to it, but it, just as before, revolves with a period of 248 Earth years around the Sun and will do so for a very long time.
More articles
Why does Easter change every year?
Historically, this happened: to calculate the day of Christ, the eastern church used the Julian calendar, and the western one ─ the Gregorian. This is one of the reasons why the day of Easter changes every year. In addition, everything changes with other representatives of confessions.
From now on, July 14 will no longer be associated in the minds of people exclusively with the bloody events that accompanied the taking of the Bastille in 1789.
Because on the same day, July 14, only in 2015, another historical event took place, this time on a global, even cosmic scale. At 14:50 Moscow time, the NASA probe " New Horizons» (New Horizons) passed the point of closest approach to Pluto.
This robotic space station was launched on January 19, 2006 to explore the ninth planet in the solar system, Pluto, and its moon Charon. It reached the Moon much faster than Apollo did in its time, and on the way to its goal, it passed Jupiter and its satellites, on which scientists tested the onboard equipment.
The New Horizons team rejoices.
But in August of the same 2006, the incredible happened: after long discussions, the International Astronomical Union deprived Pluto of the status of a full-fledged planet. However, on that day, the solar system did not shrink, as one might think, but, on the contrary, expanded unimaginably.
In connection with all this history that is happening before our eyes, we decided to tell you, dear readers, about Pluto, and about its status, and about how it all happened. And our colleagues from the magazine " fantasy world” kindly shared with us very interesting and lengthy materials on this topic.
The best image of Pluto available so far. Taken on July 13, sixteen hours before peak approach.Search for wanderers
Before the advent of telescopes in the 17th century, mankind was well aware of five celestial bodies called planets (translated from Greek - "wanderers", "wandering"): Mercury, Venus, Mars, Jupiter, Saturn. Later, two more large planets were discovered: Uranus and Neptune.
The discovery of Uranus is remarkable in that it was made by an amateur music teacher William Herschel. On March 13, 1781, he was conducting his usual survey of the sky and suddenly noticed a small yellow-green disk in the constellation Gemini. At first, Herschel considered it to be a comet, but the observations of other astronomers confirmed that a real planet was discovered with a stable elliptical orbit.
Herschel wanted to name the planet Georgia after King George III, but the astronomical community ruled that any new planet's name must match others and come from classical mythology. The planet was named Uranus after the ancient Greek god of heaven.
Amateur astronomer William Herschel, discoverer of Uranus.
But the seventh planet of the solar system stubbornly refused to follow the immutable laws of celestial mechanics, deviating from the calculated orbit. Twice astronomers developed mathematical models of the motion of Uranus, adjusted for the effect of the gravity of other planets, and twice he "deceived" them.
Then scientists suggested that Uranus is affected by another planet located beyond its orbit. On June 1, 1846, an article by the mathematician Urbain Le Verrier appeared in the journal of the French Academy of Sciences, where he described the expected position of a hypothetical celestial body. On the night of September 24, 1846, the German astronomers Johann Galle and Heinrich d'Arre, at his prompting, discovered an unknown object, which turned out to be a large planet and was subsequently named Neptune.
Planet X
These discoveries have tripled the boundaries of the solar system in just half a century. Satellites were discovered near Uranus and Neptune, which made it possible to accurately calculate the masses of the planets and their mutual gravitational influence. Based on these data, Urbain Le Verrier built the most accurate model of orbits at that time. And again, reality diverged from the calculations! A new mystery has inspired astronomers to search for a trans-Neptunian object, which has become conventionally called "Planet X".
Astronomer Clyde Tombaugh, discoverer of Pluto.
The glory of the discoverer went to the young astronomer Clyde Tombaugh. He abandoned mathematical models and engaged in persistent study of the sky with the help of a special photographic refractor. On February 18, 1930, comparing photographic plates in January, Tombaugh discovered the displacement of a faint star-shaped object - it turned out to be Pluto.
Tombo flies to Pluto
Only after launch new horizons mission chief Alan Stern confirmed rumors that some of the ashes left from the cremation of Clyde Tombaugh (he died in 1997) had been placed on board. The first photo of Pluto apparatus " New Horizons' did back in late September 2006 to test the high-definition camera. Pictures taken from a distance of approximately 4.2 billion km confirmed the ability of the device to observe space objects.
on board" new horizons» Enough instruments to map Pluto, Charon and other moons in detail, as well as to study the structure and composition of their surface. After completing work on Pluto, the device will head towards one of the Edgeworth-Kuiper belt objects. The cost of the project, including the launch vehicle and space communications services, is $650 million, which corresponds to an amount of 20 cents per US citizen annually during the ten years of the station's flight.
Soon, astronomers found that Pluto is a very small planet, smaller than the Moon, and its mass is clearly not enough to influence the movement of huge Neptune. Then Clyde Tombaugh launched a powerful search program for another "planet X", but, despite all efforts, it was not possible to find it.
Today, thanks to many years of observations and orbiting telescopes, it is known that this body has a very elongated orbit, inclined to the plane of the ecliptic (the plane of the earth's orbit) at a significant angle of 17.1 °. Such an unusual property made it possible to speculate freely on whether Pluto can be considered the home planet of the solar system, or whether it was accidentally attracted by the gravity of the Sun (this hypothesis is considered, for example, by Ivan Efremov in the novel Andromeda Nebula).
An artist's view from Pluto.
Pluto has small satellites: Charon (discovered in 1978), Hydra (2005), Nix (2005), P4 (2011) and P5 (2012). The presence of such a complex system of satellites has allowed astronomers to say that Pluto may have rarefied debris rings - such are always formed when small bodies collide in orbits around planets.
Pluto and its satellites.
Maps compiled from data from the Hubble Space Telescope have shown that Pluto's surface is not uniform. The part facing Charon contains predominantly methane ice, while the opposite side has more nitrogen and carbon monoxide ice. At the end of 2011, complex hydrocarbons were discovered on Pluto, which allowed scientists to claim that the simplest forms of life exist there. The rarefied atmosphere of Pluto, consisting of methane and nitrogen, has noticeably “swollen” in recent years, which directly indicates the presence of climate change.
Pluto based on images from the Hubble Space Telescope.
What was Pluto called?
Pluto was officially named on March 24, 1930. Astronomers chose from three options: Minerva, Kronos and Pluto, and considered the third option to be the most suitable - the name of the ancient god of the kingdom of the dead, also known as Hades and Hades.
The name was suggested by Venetia Burney, an eleven-year-old schoolgirl from Oxford. She was interested not only in astronomy, but also in classical mythology, and decided that the name Pluto perfectly suited the dark and cold world. The name came up in a conversation with her grandfather, who read about the discovery of the planet in a magazine. He conveyed Venice's proposal to Professor Herbert Turner, who telegraphed his colleagues in the United States. For her contribution to the history of astronomy, Venetia Burney received a prize of five pounds sterling.
Interestingly, Venice survived until the moment when Pluto lost its status as a planet. When asked about her attitude to this "demotion", she replied: "At my age, there is no such debate anymore, but I would like Pluto to remain a planet."
Edgeworth-Kuiper Belt
By all indications, Pluto is an ordinary planet, albeit a small one. Why did astronomers react so unfavorably to him?
The search for a hypothetical "Planet X" continued for decades, which led to many interesting discoveries. In 1992, a cluster of small bodies similar to asteroids and comet nuclei was discovered beyond the orbit of Neptune. The existence of a belt of debris left over from the formation of the solar system was predicted by the Irish engineer Kenneth Edgeworth in 1943 and the American astronomer Gerard Kuiper (in 1951).
Telescopes on Mauna Kea that discovered the Edgeworth-Kuiper belt.
The first trans-Neptunian object from the Kuiper belt was discovered by astronomers David Jewitt and Jane Lu while observing the sky with the latest technology. On August 30, 1992, they announced the discovery of the 1992 QB1 body, which they named Smiley after one of the John Le Carré characters. The name is not officially used as there is already an asteroid Smiley.
By 1995, seventeen more bodies had been found beyond the orbit of Neptune, eight of them beyond the orbit of Pluto. By 1999, the total number of registered objects of the Edgeworth-Kuiper belt exceeded one hundred, by now - over a thousand. Scientists believe that in the foreseeable future it will be possible to identify more than seventy thousand (!) Objects larger than 100 km.
It is known that all these bodies move in elliptical orbits, like real planets, and a third of them have the same orbital period as Pluto (they are called “plutinos” - “plutons”). The objects of the belt are still very difficult to classify - it is only known that they have sizes from 100 to 1000 km, and their surface is dark with a reddish tint, which indicates an ancient composition and the presence of organic compounds.
The confirmation of the Edgeworth-Kuiper hypothesis, however, did not revolutionize astronomy. Yes, now we know that Pluto is not a lonely wanderer in the abyss of space, but neighboring bodies are not able to compete with it in size, and besides, they have no atmosphere and satellites. The scientific world could continue to sleep peacefully.
And then something terrible happened!
The Edgeworth-Kuiper belt as seen by an artist.
Oplutonili
Society reacted differently to the decision of the International Astronomical Union: some did not attach any importance, while others were even more convinced that scientists were fooling around. The authorities of the states of New Mexico and Illinois, where Clyde Tombo lived and worked, decided by law to retain the status of a planet for Pluto and declared March 13 the annual Day of the planet Pluto.
The verb “to pluto” (“to pluto”) appeared in English, recognized as the word of 2006 by the American Dialectological Society. The word means "decrease in value or value."
Ordinary citizens responded with both online petitions and street protests. It was difficult for people who had considered Pluto a planet all their lives to get used to the decision of astronomers. In addition, Pluto was the only planet discovered by an American.
distant worlds
Astronomer Mike Brown, in his memoirs, claims that even as a child, through observations, he independently discovered the planets, unaware of their existence. Becoming a specialist, he dreamed of the greatest discovery - "Planet X". And he opened it. And not just one, but sixteen.
The surface of Sedna as seen by an artist.
The first trans-Neptunian object, designated 2001 YH140, was discovered by Mike Brown and Chadwick Trujillo in December 2001. It was a standard Edgeworth-Kuiper belt celestial body, about 300 km in diameter. The astronomers continued their search, and on June 4, 2002, the team discovered the much larger object 2002 LM60, 850 km in diameter (now estimated at 1170 km). That is, the size of 2002 LM60 is comparable to the size of Pluto (2302 km). Later, this body, which looks like a full-fledged planet, was called Quaoar - after the creator god worshiped by the Tongva Indians of Southern California.
Further more. On November 14, 2003, Brown's team discovers the trans-Neptunian object 2003 VB12, named Sedna, after the Eskimo goddess of the sea, who lives at the bottom of the Arctic Ocean. At first, the diameter of this celestial body was estimated at 1800 km. Additional observations with the Spitzer Orbiting Telescope reduced the estimate to 1,600 km, but Sedna is now thought to be 995 km. Spectroscopic analysis has shown that Sedna's surface is similar to some other trans-Neptunian objects. It moves in a very elongated orbit, and scientists believe that it was once influenced by a star that passed by the solar system.
Quaoar as imagined by the artist.
Harvest planets
I must say that Pluto is the only one who lost in status, the rest of the dwarf planets were previously classified as asteroids. Among them is Ceres (named after the Roman goddess of fertility), discovered in 1801 by the Italian astronomer Giuseppe Piazzi.
For some time, Ceres was considered the very missing planet between Mars and Jupiter, but later it was assigned to asteroids (this term was specifically introduced precisely after the discovery of Ceres and neighboring large objects).
Ceres, whose diameter reaches 950 km, is located in the asteroid belt, which seriously complicates its observation. By the decision of the astronomical union in 2006, Ceres began to be considered a dwarf planet. The dwarf planet is hypothesized to have an icy mantle or even oceans of liquid water below the surface.
A qualitative step in the study of Ceres was the mission of the Rassvet interplanetary apparatus, which reached this celestial body on March 6, 2015, becoming the first spacecraft delivered into the orbit of a dwarf planet.
On February 17, 2004, Mike Brown discovered the object 2004 DW, named Orc (deity of the underworld in Etruscan and Roman mythologies), with a diameter of 946 km. Spectral analysis of Ork showed that it is covered with water ice. Most of all, Orc is similar to Charon - a satellite of Pluto.
On December 28, 2004, Mike Brown discovered object 2003 EL61, named Haumea (the Hawaiian goddess of fertility), with a diameter of about 1300 km. Later it turned out that Haumea rotates very quickly, making one revolution around its axis in four hours. Accordingly, its shape should be strongly elongated.
Modeling showed that in this case, the longitudinal size of Haumea should be close to the diameter of Pluto, and the transverse size - half as much. Perhaps Haumea appeared as a result of the collision of two celestial bodies. Upon impact, a significant amount of light components partially evaporated, partially ejected into space, subsequently forming two satellites - Hiiaka and Namaka.
Haumea as seen by the artist.
goddess of discord
Mike Brown's finest hour struck on January 5, 2005, when his team discovered a trans-Neptunian object estimated to be 3,000 km in diameter (later measurements gave a diameter of 2,326 km). Thus, a celestial body larger than Pluto was found in the Edgeworth-Kuiper belt. Scientists made a noise: the tenth planet has finally been discovered!
After the discovery of a new planet, astronomers gave her the unofficial name of Xena in honor of the heroine of the popular fantasy television series. Well, when Xena found a companion, he was immediately named Gabrielle, because that was the name of the permanent companion of the warrior queen.
But the International Astronomical Union could not accept such "frivolous" names, so Xena was renamed Eris (Greek goddess of discord), and Gabriel - Dysnomia (Greek goddess of lawlessness).
Eris has indeed caused discord among astronomers. Logically, Xena-Eris should have been recognized as the tenth planet, and the Michael Brown group should have been entered into the annals of history as its discoverers. But it was not there!
Previous discoveries have indicated that there may be dozens more objects lurking in the Edgeworth-Kuiper belt that are comparable in size to Pluto. Which is easier - multiplying the number of planets, rewriting astronomy textbooks every couple of years, or throwing Pluto off the list, and with it all the newly discovered celestial bodies?
We won't be found!
The American interplanetary spacecraft "Pioneer-10" and "Pioneer-11", which went into flight in the early seventies, placed aluminum plates with a message to aliens. In addition to images of a man, a woman and directions to find us in the galaxy, there is a diagram of the solar system, which included nine planets, along with Pluto.
The devices have long flown away, and it is impossible to correct the information on the plates. It turns out that if someday the "brothers in mind", guided by the "Pioneers" scheme, want to find us, they are very likely to pass by, confused in the number of planets. True, if it turns out to be evil alien invaders, you can always say that we purposely confused them.
The verdict was passed by Mike Brown himself, having discovered on March 31, 2005 the object 2005 FY9 with a diameter of 1500 km, named Makemake (the creator god of mankind in the mythology of the Rapanui people, the indigenous inhabitants of Easter Island). The patience of the colleagues ran out, and they gathered at the conference of the International Astronomical Union in Prague to determine once and for all what a planet is.
During the debate, scientists decided that a planet can be considered a celestial body that revolves around the Sun, is not among the satellites of another planet, has sufficient mass to acquire a spherical shape, and “cleared” the neighborhood of its orbit from bodies of comparable size.
This decision drew criticism and ridicule. Pluto scientist Alan Stern said that if this definition were applied to Earth, Mars, Jupiter and Neptune, in whose orbits asteroids were found, then they should also be stripped of the title of planets. According to him, less than 5% of astronomers voted for the decision, and their opinion cannot be considered universal.
The largest trans-Neptunian objects in comparison with the Earth.
However, Mike Brown himself accepted the definition of the International Astronomical Union, content with the fact that the discussion finally ended to everyone's satisfaction. And indeed - the storm subsided, the astronomers went to their observatories.
* * *
So far it seems that the classification of Pluto, Eris, Sedna, Haumea and Quaoar is unlikely to ever be revised. And only Mike Brown is not discouraged - he is sure that in the coming years, a celestial body the size of Mars will be found at the far edge of the Edgeworth-Kuiper belt. It's terrible to imagine what will happen then!
Having lost the status of a planet, Pluto has become an inexhaustible source of inspiration for Internet creativity.
Yes, yes, it's true. Pluto is no longer a planet. Didn't you know? This "fresh" information appeared a little over 10 years ago. However, according to estimates "by eye", about half of the adult visitors to planetariums are surprised by this fact. But the children in this matter are at their best, they know for sure that there are eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune). But to the question "Why is Pluto no longer a planet?" may not always be answered. Why did they do this to him and who are these "scoundrels," explains astronomer, lecturer at the St. Petersburg Planetarium Maria Borukha.
So what happened to Pluto back in 2006?
Some people believe that Pluto has left the solar system. We hasten to reassure: Pluto is in place and has not left us. It still revolves around the Sun with a period of 248 Earth years and, most likely, will do so for a very, very long time.
It's all about the names that astronomers use to classify objects. It was they who decided not to call Pluto the word "planet" anymore.
Imagine that one child gave another toy. There used to be Petya the engine, and Colin the engine became. Although the toy itself has not changed at all, we began to call it differently. Something similar happened to the waters of the Indian, Pacific and Atlantic oceans surrounding Antarctica - in 2000 they were recognized as a separate Southern Ocean.
Same with Pluto:Until 2006, Pluto was called the "planet" of the solar system, and now it is called the "dwarf planet". It is important that dwarf planets (they are marked with arrows in the figure below) are not a subclass of "planets" (they can also be easily distinguished in the image) - this is a new type of object in the solar system, which was introduced in that same 2006. Now it includes five objects: Ceres, Pluto, Haumea, Makemake and Eris.
How are planets and dwarf planets different?
It can be seen from the figure above that, firstly, all dwarf planets are smaller than planets. So maybe Pluto is just too small or light to be called a real planet? And this was only discovered in 2006?
No, the size of Pluto was known accurately enough until 2006 to conclude that it is not much, but smaller than Mercury (the status of the smallest planet passed to it).
Moreover, many bodies of the solar system, even larger than Mercury, are not included in the list of planets (for example, Ganymede is the largest satellite of Jupiter). And our Moon, a well-known cosmic body from ancient times, is, of course, smaller than Mercury, but at the same time larger than Pluto!
Yes, if the Moon lived separately from the Earth and revolved around the Sun, it could receive the status of a planet. Now it is called a satellite and is unlikely to change its status in the near future.
We understand this word intuitively and say that the Moon is a satellite of the Earth, and the Earth is a satellite of the Sun, implying the movement of one body around another. But formalizing the definition of this term has proved so difficult that the International Astronomical Union has not yet introduced a precise definition of the word "satellite".
Now we can come to the conclusion: in order to be called a planet, it is important not only to be a sufficiently large body, but it is also necessary to be a satellite of the Sun, and not another body.
But Pluto fits that definition! Maybe he, being a large body, flies in some special orbit around the Sun?
Partly yes.
With this drawing, you can almost accurately represent the scale of the solar system and the position of the orbits of the planets. It is striking that the orbit of Pluto is strongly inclined - by as much as 17 degrees in relation to the plane in which the Earth's orbit lies. Next comes Mercury, whose inclination is only 7 degrees.
In addition to its anomalously high inclination, Pluto's orbit is more elongated than the orbits of the planets, although the difference from Mercury in this parameter is small.
Maybe this is the answer: Pluto's orbit is too elongated and too tilted?
Let's now look at the orbits of bodies that are farther from the Sun than Pluto (they are highlighted in red in the figure below). This can be done more clearly with the help of this resource.
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Dwarf planets of the solar system. Photo:
So what property is common to such different objects, which at the same time distinguishes them from the planets?
It turns out that it is necessary to consider not only the bodies themselves, their size and orbit, but also pay attention to what is in their vicinity: the small bodies of the solar system are mostly asteroids.
It is in this region of the solar system that main asteroid belt lives one of the dwarf planets - Ceres. By the way, the classification of this object was also changed: earlier, Ceres was considered an asteroid (it was the first discovered celestial body of its kind), and now it is one of the dwarf planets.
The difference between asteroids and dwarf planets is in their shape. Dwarf planets are massive enough to be round, while asteroids are lighter bodies and have irregular shapes.
The other four dwarf planets live much farther from the Sun, beyond the orbit of Neptune. And in the same region of the solar system is the Kuiper belt - another asteroid belt.
Now we can conclude that the dwarf planets of the solar system differ from the planets mainly in the presence of asteroids in the vicinity of their orbits.
At the same time, dwarf planets and planets have a rounded shape and revolve around the Sun.
And what was the reason to lower the status of Pluto?
Ideas that Pluto should no longer have the status of a planet began to appear at the beginning of the 21st century. After 70 years of Pluto's tenure as the ninth planet, one after another, discoveries of bodies that are further than Pluto, but comparable in size and mass, rained down. The final chord in the sequence of discoveries was the discovery of Eris in 2005 by a group of scientists led by Michael Brown. Subsequently, he even wrote the book "How I Killed Pluto."
The fact is that Eris turned out to be significantly more massive than Pluto and actually began to claim the role of the 10th planet. Scientists had a choice: to continue expanding the list of planets, or to come up with a definition for the word planet that would ensure peace and stability in their family. They chose the second path and gave the following definition to the word planet:
- A body that revolves around the sun.
- Massive enough to take on a near-circular shape under the influence of gravity forces, and in a state of hydrostatic equilibrium.
- Clearing the space of its orbit from other bodies.
Does this mean that the list of planets will never be replenished again? In no case! Until now, new objects, usually small ones, are regularly discovered in the solar system. But even with the existing variety of powerful telescopes, a planet the size of the Earth, but located 500 times farther from the Sun than the Earth itself, astronomers would not be able to notice. Moreover, in January 2016, the same "Pluto killer" Michael Brown predicted the existence of a large planet (10 times more massive than the Earth!) On the visible outskirts of the solar system. During 2016, this hypothetical object (predicted theoretically, but not necessarily existing in reality) was not found. But it is possible that in the coming years, astronomers will find a real ninth planet that will be more worthy of this status than Pluto.
