Our Solar System consists of the Sun, the planets orbiting it, and smaller celestial bodies. All of these are mysterious and surprising because they are still not fully understood. Below will be indicated the sizes of the planets of the solar system in ascending order, and a brief description of the planets themselves.
There is a well-known list of planets, in which they are listed in order of their distance from the Sun:
Pluto used to be in last place, but in 2006 it lost its status as a planet, as larger celestial bodies were found further away from it. The listed planets are divided into rocky (inner) and giant planets.
Brief information about rocky planets
The inner (rocky) planets include those bodies that are located inside the asteroid belt separating Mars and Jupiter. They got their name “stone” because they consist of various hard rocks, minerals and metals. They are united by a small number or absence of satellites and rings (like Saturn). On the surface of rocky planets there are volcanoes, depressions and craters formed as a result of the fall of other cosmic bodies.
But if you compare their sizes and arrange them in ascending order, the list will look like this:
Brief information about the giant planets
The giant planets are located beyond the asteroid belt and therefore are also called outer planets. They consist of very light gases - hydrogen and helium. These include:
But if you make a list by the size of the planets in the solar system in ascending order, the order changes:
A little information about the planets
In modern scientific understanding, a planet means a celestial body that revolves around the Sun and has sufficient mass for its own gravity. Thus, there are 8 planets in our system, and, importantly, these bodies are not similar to each other: each has its own unique differences, both in appearance and in the components of the planet themselves.
- This is the planet closest to the Sun and the smallest among the others. It weighs 20 times less than the Earth! But, despite this, it has a fairly high density, which allows us to conclude that there are a lot of metals in its depths. Due to its strong proximity to the Sun, Mercury is subject to sudden temperature changes: at night it is very cold, during the day the temperature rises sharply.
- This is the next planet closest to the Sun, in many ways similar to Earth. It has a more powerful atmosphere than Earth and is considered a very hot planet (its temperature is above 500 C).
- This is a unique planet due to its hydrosphere, and the presence of life on it led to the appearance of oxygen in its atmosphere. Most of the surface is covered with water, and the rest is occupied by continents. A unique feature is the tectonic plates, which move, albeit very slowly, resulting in changes in the landscape. The Earth has one satellite - the Moon.
– also known as the “Red Planet”. It gets its fiery red color from a large amount of iron oxides. Mars has a very thin atmosphere and much lower atmospheric pressure compared to Earth. Mars has two satellites - Deimos and Phobos.
is a real giant among the planets of the solar system. Its weight is 2.5 times the weight of all the planets combined. The surface of the planet consists of helium and hydrogen and is in many ways similar to the sun. Therefore, it is not surprising that there is no life on this planet - there is no water and a solid surface. But Jupiter has a large number of satellites: 67 are currently known.
– This planet is famous for the presence of rings consisting of ice and dust revolving around the planet. With its atmosphere it resembles that of Jupiter, and in size it is slightly smaller than this giant planet. In terms of the number of satellites, Saturn is also slightly behind - it has 62 known. The largest satellite, Titan, is larger than Mercury.
- the lightest planet among the outer ones. Its atmosphere is the coldest in the entire system (minus 224 degrees), it has a magnetosphere and 27 satellites. Uranium consists of hydrogen and helium, and the presence of ammonia ice and methane has also been noted. Because Uranus has a high axial tilt, it appears as if the planet is rolling rather than rotating.
- despite its smaller size than , it is heavier and exceeds the mass of the Earth. This is the only planet that was found through mathematical calculations, and not through astronomical observations. The strongest winds in the solar system were recorded on this planet. Neptune has 14 moons, one of which, Triton, is the only one that rotates in the opposite direction.
It is very difficult to imagine the entire scale of the solar system within the limits of the studied planets. It seems to people that the Earth is a huge planet, and, in comparison with other celestial bodies, it is so. But if you place giant planets next to it, then the Earth already takes on tiny dimensions. Of course, next to the Sun, all celestial bodies appear small, so representing all the planets in their full scale is a difficult task.
The most famous classification of planets is their distance from the Sun. But a listing that takes into account the sizes of the planets of the Solar System in ascending order would also be correct. The list will be presented as follows:
As you can see, the order has not changed much: the inner planets are on the first lines, and Mercury occupies the first place, and the outer planets occupy the remaining positions. In fact, it doesn’t matter at all in what order the planets are located, this will not make them any less mysterious and beautiful.
The new words couldn’t fit into my head. It also happened that a natural history textbook set us the goal of remembering the location of the planets of the solar system, and we were already selecting means to justify it. Among the many options for solving this problem, there are several interesting and practical ones.
Mnemonics in its purest form
The ancient Greeks came up with a solution for modern students. It is not for nothing that the term “mnemonics” comes from a consonant Greek word, literally meaning “the art of remembering.” This art gave rise to a whole system of actions aimed at memorizing a large amount of information - “mnemonics”.
They are very convenient to use if you simply need to store in memory a whole list of any names, a list of important addresses or telephone numbers, or remember the sequence of location of objects. In the case of the planets of our system, this technique is simply irreplaceable.
We play association or “Ivan gave birth to a girl...”
Each of us remembers and knows this poem from elementary school. This is a mnemonic counting rhyme. We are talking about that couplet, thanks to which it becomes easier for a child to remember the cases of the Russian language - “Ivan Gave Birth to a Girl - Ordered to Drag the Diaper” (respectively - Nominative, Genitive, Dative, Accusative, Instrumental and Prepositional).
Is it possible to do the same with the planets of the solar system? - Undoubtedly. Quite a large number of mnemonics have already been invented for this astronomical educational program. The main thing you need to know is that they are all based on associative thinking. For some it is easier to imagine an object similar in shape to the one being remembered, for others it is enough to imagine a chain of names in the form of a kind of “cipher”. Here are just a few tips on how best to record their location in memory, taking into account their distance from the central star.
Funny pictures
The order in which the planets of our star system move away from the Sun can be remembered through visual images. To begin, associate with each planet an image of an object or even a person. Then imagine these pictures one by one, in the sequence in which the planets are located inside the Solar System.
- Mercury. If you have never seen images of this ancient Greek god, try to remember the late lead singer of the group “Queen” - Freddie Mercury, whose surname is similar to the name of the planet. It is unlikely, of course, that children can know who this uncle is. Then we suggest coming up with simple phrases where the first word would begin with the syllable MER, and the second with KUR. And they must necessarily describe specific objects, which will then become a “picture” for Mercury (this method can be used as the most extreme option with each of the planets).
- Venus. Many people have seen the statue of Venus de Milo. If you show her to children, they will easily be able to remember this “armless aunt.” Plus, educate the younger generation. You can ask them to remember some acquaintance, classmate or relative with that name - in case there are such people in their social circle.
- Earth. Everything is simple here. Everyone must imagine themselves, an inhabitant of the Earth, whose “picture” stands between two planets located in space before and after ours.
- Mars. In this case, advertising can become not only an “engine of trade,” but also of scientific knowledge. We think you understand that you need to imagine the popular imported chocolate bar in place of the planet.
- Jupiter. Try to imagine some landmark of St. Petersburg, for example, the Bronze Horseman. Yes, even though the planet begins in the south, the locals call the “Northern capital” St. Petersburg. For children, such an association may not be beneficial, so invent a phrase with them.
- Saturn. Such a “handsome man” does not need any visual image, because everyone knows him as a planet with rings. If you still have difficulties, imagine a sports stadium with a running track. Moreover, such an association has already been used by the creators of one animated film on a space theme.
- Uranus. The most effective in this case will be a “picture” in which someone is very happy about some achievement and seems to shout “Hurray!” Agree - every child is capable of adding one letter to this exclamation.
- Neptune. Show your children the cartoon "The Little Mermaid" - let them remember Ariel's dad - the King with a mighty beard, impressive muscles and a huge trident. And it doesn’t matter that in the story His Majesty’s name is Triton. Neptune also had this tool in his arsenal.
Now, once again mentally imagine everything (or everyone) that reminds you of the planets of the solar system. Flip through these images, like pages in a photo album, from the first “picture”, which is closest to the Sun, to the last, whose distance from the star is the greatest.
“Look, what kind of rhymes have turned out...”
Now - to mnemonics, which are based on the “initials” of the planets. Remembering the order of the planets of the solar system is indeed easiest to do by the first letters. This type of “art” is ideal for those who have less developed imaginative thinking, but are fine with its associative form.
The most striking examples of versification in order to record the order of planets in memory are the following:
“The Bear Comes Out Behind the Raspberry - The Lawyer Managed to Escape the Lowlands”;
“We Know Everything: Yulia’s Mom Stood on Stilts in the Morning.”
You can, of course, not write a poem, but simply choose words for the first letters in the names of each of the planets. A little advice: in order not to confuse the places of Mercury and Mars, which begin with the same letter, put the first syllables at the beginning of your words - ME and MA, respectively.
For example: In some places Golden Cars could be seen, Julia seemed to see Us.
You can come up with such proposals ad infinitum - as much as your imagination allows. In a word, try, practice, remember...
The study of planets is carried out both with the help of ground-based astronomical instruments installed in observatories and with the help of spacecraft.
Planet Earth
Numerous photographs of the Earth obtained from spacecraft make it possible to see the three main shells of the globe: the atmosphere and its clouds, the hydrosphere and the lithosphere with its natural covers. Most of the planets in the solar system have an atmosphere; a solid shell is characteristic of terrestrial planets, satellites of planets and asteroids. The Earth's hydrosphere is a unique phenomenon in the solar system; no other known planet has it. After all, for water to exist in liquid form, certain conditions are required: temperature and pressure. Water is a very common chemical compound in the Universe, but on other celestial bodies we encounter water mainly in its solid phase, also known on Earth in the form of snow, frost and ice. The thickness of the crust is very small: from 10 km under the oceans to 80 km under mountain ranges. The core has a radius half that of the planet, and between the core and the crust there is an intermediate layer - the Earth's mantle, consisting of substances denser than in the crust.
The gas envelope - the atmosphere surrounding the Earth, contains 78% nitrogen, 21% oxygen and a negligible amount of other gases.
The lower layer of the atmosphere is called the troposphere, which extends to an altitude of 10-12 km (in mid-latitudes). In it, the temperature drops with increasing altitude. Higher up, in the stratosphere, it remains almost constant, about -40 °C. From an altitude of about 25 km, the temperature of the earth's atmosphere slowly increases due to the absorption of ultraviolet radiation from the Sun.
The atmosphere reflects or absorbs most of the radiation coming to the Earth from outer space. For example, it does not transmit X-ray radiation from the Sun. The atmosphere protects us both from the continuous bombardment of micrometeorites and from the destructive effects of cosmic rays - streams of fast-flying particles (mainly protons and nuclei of helium atoms).
The atmosphere plays a critical role in the Earth's heat balance. Visible solar radiation can pass through it with almost no attenuation. It is absorbed by the earth's surface, which heats up and emits infrared rays. The Earth's magnetic field is quite large (about 5 x 10 -5 T). With distance from the Earth, the magnetic field induction weakens.
Moon
The origin of the Moon has not yet been definitively established. Three different hypotheses have been most developed. At the end of the 19th century. J. Darwin put forward a hypothesis according to which the Moon and the Earth originally constituted one common molten mass, the speed of rotation of which increased as it cooled and contracted; as a result, this mass was torn into two parts: a larger one - the Earth and a smaller one - the Moon. This hypothesis explains the low density of the Moon, formed from the outer layers of the original mass. However, it encounters serious objections from the point of view of the mechanism of such a process; In addition, there are significant geochemical differences between the rocks of the Earth's shell and the lunar rocks.
THE MOON is the only natural satellite of the Earth and the closest celestial body to us; the average distance to the Moon is 384,000 kilometers.
The Moon moves around the Earth at an average speed of 1.02 km/s in a roughly elliptical orbit in the same direction in which the vast majority of other bodies in the Solar System move, that is, counterclockwise when looking at the Moon's orbit from the North Pole. The semimajor axis of the Moon's orbit, equal to the average distance between the centers of the Earth and the Moon, is 384,400 km (approximately 60 Earth radii). The period of revolution of the Moon around the Earth, the so-called sidereal (stellar) month, is 27.32166 days. The shape of the Moon is very close to a sphere with a radius of 1737 km, which is equal to 0.2724 of the equatorial radius of the Earth. The mass of the Moon is most accurately determined from observations of its artificial satellites. It is 81 times less than the mass of the Earth. The average density of the Moon is 3.34 g/cm 3 (0.61 the average density of the Earth). The acceleration of gravity on the surface of the Moon is 6 times less than on Earth.
Relief of the lunar surface
The relief of the lunar surface was mainly clarified as a result of many years of telescopic observations. The “lunar seas,” occupying about 40% of the visible surface of the Moon, are flat lowlands intersected by cracks and low winding ridges. Many seas are surrounded by concentric ring ridges. The remaining, lighter surface is covered with numerous craters, ring-shaped ridges, grooves, and so on. Craters smaller than 15-20 kilometers have a simple cup shape; larger craters (up to 200 kilometers in diameter) consist of a rounded shaft with steep internal slopes, have a relatively flat bottom, deeper than the surrounding terrain, often with a central hill.
Craters on the lunar surface have different relative ages: from ancient, barely visible, highly reworked formations to very clear-cut young craters, sometimes surrounded by light “rays”. Due to the absence of an atmosphere and hydrosphere, a significant part of these craters has survived to this day. Nowadays, meteorites fall on the Moon much less frequently; volcanism also largely ceased as the Moon used up a lot of thermal energy and radioactive elements were carried into the outer layers of the Moon.
The uppermost layer of the Moon is represented by the crust, the thickness of which, determined only in the basin areas, is 60 km. It is very likely that on the vast continental areas of the far side the crust is approximately 1.5 times thicker. The crust is composed of igneous crystalline rocks - basalts. Under the crust is the mantle, which, like the earth’s, can be divided into upper, middle and lower. The thickness of the upper mantle is about 250 km, and the middle is about 500 km, and its boundary with the lower mantle is located at a depth of about 1000 km. At the very center, there appears to be a small liquid core with a radius of less than 350 kilometers. The core can be iron sulfide or iron; in the latter case it should be smaller, which is in better agreement with estimates of the density distribution over depth. Its mass probably does not exceed 2% of the mass of the entire Moon. The temperature in the core depends on its composition and, apparently, lies within the range of 1300 - 1900 K.
Terrestrial planets
The terrestrial planets - Mercury, Venus, Earth and Mars - differ from the giant planets in their smaller sizes, lower mass, higher density, slower rotation, much thinner atmospheres, and a small number of satellites or their absence.
Mercury
It is the closest planet to the Sun, slightly larger than the Moon, but its average density is almost the same as that of the Earth. Radar observations have detected an extremely slow rotation of Mercury. Its sidereal day, i.e. the period of rotation around the axis relative to the stars is equal to 58.65 of our days. A solar day on this planet (that is, the period of time between successive noons) is about 176 Earth days. They are equal to two Mercury years, since Mercury makes one revolution around the Sun in 88 Earth days.
There is virtually no atmosphere on Mercury. Therefore, its daytime hemisphere becomes very hot. Temperatures of more than 400°C have been measured at a subsolar point on Mercury. At this temperature, lead, tin and even zinc melt. The surface of Mercury is dotted with craters so that in photographs it is difficult to distinguish it from the surface of the Moon.
Venus
Venus is the same size as Earth, and its mass is more than 80% of Earth's mass. Located closer to the Sun than our planet, Venus receives more than two times more light and heat from it than Earth.
Venus comes closer to Earth than any other planet. But the dense, cloudy atmosphere does not allow you to directly see its surface. Radar images show a very wide variety of craters, volcanoes and mountains. Surface temperatures are hot enough to melt lead, and the planet may once have had vast oceans. Venus has an almost circular orbit, which it travels around in 225 Earth days at a distance of 108.2 million km from the Sun. Venus rotates around its axis in 243 Earth days - the longest time among all the planets. Around its axis, Venus rotates in the opposite direction, that is, in the direction opposite to its orbital movement. Venus is only slightly smaller in size than Earth, and its mass is almost the same. For these reasons, Venus is sometimes called Earth's twin or sister. However, the surface and atmosphere of these two planets are completely different. On Earth there are rivers, lakes, oceans and the atmosphere that we breathe. Venus is a searingly hot planet with a thick atmosphere that would be fatal to humans.
Mars
Mars is half the diameter of Earth. Its orbit has a significant eccentricity, so when Mars is at opposition near perihelion, it shines in the sky, second only to Venus in brightness. Such confrontations are called great and are repeated after 15 and 17 years.
The year of Mars is almost twice as long as the Earth's, there is also a change of seasons, since the axis of the daily rotation of Mars is inclined to the plane of its orbit, almost like the Earth's.
It turned out that the planet’s atmosphere is very rarefied and its pressure is about 100 times less than Earth’s. Basically, it consists of carbon dioxide, oxygen and very little water vapor.
Conditions on Mars are harsh. Daily temperature changes on Mars reach 80-100°C.
Occasionally, powerful dust storms occur on Mars, sometimes lasting for months, lifting colossal amounts of tiny dust particles into the atmosphere. Thus, the existence of sandy deserts there is confirmed, which determined the orange color of Mars as a whole. Judging by dust storms, there can be strong winds on Mars, blowing at speeds of tens of meters per second.
Mars, like the Moon and Mercury, is dotted with craters. The shape of Martian craters indicates the phenomena of weathering and leveling of its surface. Several gigantic, apparently long-extinct volcanoes have been discovered on Mars. The height of the largest of them is 27 km. The magnetic field of Mars is much weaker than that of Earth.
Planets are giants
The solar system is a system of celestial bodies welded together by the forces of mutual attraction. It includes: the central body the Sun, 9 large planets with their satellites (of which more than 60 are now known), several thousand small planets, or asteroids (over 5 thousand have been discovered, in reality there are much more), several hundred observed comets and countless meteor bodies. The large planets are divided into two main groups: the terrestrial planets - Mercury, Venus, Earth and Mars, and the Jupiter group planets, or giant planets: Jupiter, Saturn, Uranus, Neptune. Between the orbits of Mars and Jupiter there is a belt of small planets - asteroids. About 2 thousand of them have been well studied, their orbits have been calculated, their sizes have been established, and the asteroids themselves have been given names. Beyond the asteroid belt, the kingdom of the giant planets begins. There are four of them: Jupiter, Saturn, Uranus and Neptune. The largest of them is Jupiter. It is 1300 times larger in volume than the Earth. Giant planets also have very significant masses. The mass of Jupiter is equal to 318 Earth masses, Saturn -95. All planets in this group rotate rapidly around their axes. A day on Neptune lasts 15 hours 48 minutes. On Jupiter - 9 hours 50 minutes. The chemical composition of the giants is mainly hydrogen-helium based. The average density of their substance is very low. Apparently, giant planets do not have a solid surface. A large number of satellites move around the giant planets.
Table 1. Comparative characteristics of the Planets
| Characteristics of the Planet | Jupiter | Saturn | Uranus | Neptune |
| Radius | 12 R 3 | 10 R W | 4 R W | 4 R W |
| Weight | 318 m3 | 95 m W | 15 m W | 17 m W |
| Density | 1.3 g/cm W | 0.7 g/cm W | 1.3 g/cm W | 1.6 g/cm W |
| Day | 10 o'clock | 10 o'clock | 17:00 | 16 hours |
| From the Sun | 5 a.u. | 10 a.u. | 19 a.u. | 30 a.u. |
| Year | 12 years | 30 years | 84 years old | 165 years |
| Rings | Yes | Yes | Yes | Yes |
| Satellites | 28 | 30 | 17 | 8 |
| Axis of rotation |
Jupiter
Jupiter is surrounded by a thick atmosphere consisting mainly of hydrogen. Helium makes up about 11% of the planet's gaseous envelope by volume. Jupiter's mass is 318 times greater than the mass of Earth. It moves in orbit at a speed of 13 km/s and makes a full revolution around the Sun in 12 Earth years. It rotates very quickly around its axis. His day is 9 hours 50 minutes. Jupiter has a strong magnetic field. This leads to the appearance of auroras in the planet's atmosphere.
Saturn
The most beautiful planet. It completes a full revolution around the Sun in 30 Earth years. A Red Spot has been discovered in the atmosphere. Among the planets, Saturn stands out for its unusual appearance: it has formations - rings encircling its central core. According to theoretical calculations based on astronomical observations and data obtained using spacecraft, the internal structure has much in common with the structure of Jupiter. In the very center is a liquid core, surrounded by an outer core of CH 4, NH 3 and H 2 O. And the outer core is surrounded by a belt of metallic hydrogen.
Uranus
Uranus was discovered by the English scientist Herschel in 1781. A year on Uranus lasts 84 Earth years, and a day is almost equal to an Earth day. Unlike other planets, Uranus seems to lie on its side. Its rotation axis is located in the orbital plane. Uranium is composed of hydrogen and helium. But since the average density is slightly higher than the density of Jupiter and Saturn, it can be assumed that the planet contains an increased amount of helium or a core of heavy metals. In 1977, rings were discovered around Uranus.
Neptune
The farthest of the giant planets is Neptune. A year lasts 165 Earth years. The average density of matter at Neptune is even higher than that of Uranus; apparently, it has a core of silicates, metals and other non-metals that are part of the terrestrial planets.
Features of the structure of giant planets
The most important structural feature is that these planets do not have solid surfaces. This idea is in good agreement with low and medium densities, their chemical composition (they consist mainly of light elements - hydrogen and helium), fast zonal rotation, and some other data.
Asteroids
Minor planets, or asteroids, mainly orbit between the orbits of Mars and Jupiter, and are invisible to the naked eye. The first minor planet was discovered in 1801, and according to tradition it was called one of the names of Greco-Roman mythology - Ceres. Soon other small planets were found, called Pallas, Vesta and Juno. Currently, more than 3,000 asteroids are known. Over billions of years, asteroids collide with each other from time to time.
The brightest asteroid, Vesta, is no brighter than 6th magnitude. The largest asteroid is Ceres. Its diameter is about 800 km. The smallest known asteroids have diameters of only about a kilometer. Of course, asteroids have no atmosphere. In the sky, small planets look like stars, which is why they were called asteroids, which translated from ancient Greek means “star-like.” The orbits of some asteroids have unusually large eccentricities. As a result, at perihelion they approach the Sun closer than Mars and Earth, and Icarus is closer than Mercury. In 1968, Icarus approached the Earth at a distance of less than 10 million kilometers, but its insignificant gravity had no effect on the Earth.
Fireballs and meteorites
A fireball is a rather rare phenomenon - a fireball flying across the sky. This phenomenon is caused by the intrusion of large solid particles called meteoroids into the dense layers of the atmosphere. Moving in the atmosphere, the particle heats up due to braking, and an extensive luminous shell consisting of hot gases forms around it. Fireballs often have a noticeable angular diameter and are visible even during the day.
A meteoroid of small size sometimes evaporates entirely in the Earth's atmosphere. In most cases, its mass decreases greatly during the flight, and only the remnants reach the Earth, usually having time to cool down when the escape velocity has already been extinguished by air resistance.
There are three types of meteorites known: stone, iron and stone-iron. Sometimes meteorites are found many years after they fell. Especially many iron meteorites have been found.
Comets
Being in space far from the Sun, comets look like very faint, blurry, light spots, in the center of which is the nucleus. Only those comets that pass relatively close to the Sun become very bright and “tailed.” The appearance of a comet from the Earth also depends on the distance to it, the angular distance from the Sun, the light of the Moon, etc. Halley's Comet is one of the periodic comets. Many short-period comets are now known with orbital periods of three ( Comet Encke) up to ten years. Their aphelions lie near the orbit of Jupiter. The approach of Comets to the Earth and their future apparent path across the sky are calculated in advance with great accuracy. Along with this, there are comets moving in very elongated orbits with long orbital periods. We mistake their orbits for parabolas, although in reality they appear to be very elongated ellipses, but it is not easy to distinguish these curves, knowing only a small segment of the path of comets near the Earth and the Sun. Most comets do not have a tail and are only visible through a telescope.
There are no specific recommendations for this topic. Read the material carefully. We wish you success.On March 13, 1781, English astronomer William Herschel discovered the seventh planet of the solar system - Uranus. And on March 13, 1930, American astronomer Clyde Tombaugh discovered the ninth planet of the solar system - Pluto. By the beginning of the 21st century, it was believed that the solar system included nine planets. However, in 2006, the International Astronomical Union decided to strip Pluto of this status.
There are already 60 known natural satellites of Saturn, most of which were discovered using spacecraft. Most of the satellites consist of rocks and ice. The largest satellite, Titan, discovered in 1655 by Christiaan Huygens, is larger than the planet Mercury. The diameter of Titan is about 5200 km. Titan orbits Saturn every 16 days. Titan is the only moon to have a very dense atmosphere, 1.5 times larger than Earth's, consisting primarily of 90% nitrogen, with moderate methane content.
The International Astronomical Union officially recognized Pluto as a planet in May 1930. At that moment, it was assumed that its mass was comparable to the mass of the Earth, but later it was found that Pluto’s mass is almost 500 times less than the Earth’s, even less than the mass of the Moon. Pluto's mass is 1.2 x 10.22 kg (0.22 Earth's mass). Pluto's average distance from the Sun is 39.44 AU. (5.9 to 10 to 12 degrees km), radius is about 1.65 thousand km. The period of revolution around the Sun is 248.6 years, the period of rotation around its axis is 6.4 days. Pluto's composition is believed to include rock and ice; the planet has a thin atmosphere consisting of nitrogen, methane and carbon monoxide. Pluto has three moons: Charon, Hydra and Nix.
At the end of the 20th and beginning of the 21st centuries, many objects were discovered in the outer solar system. It has become obvious that Pluto is only one of the largest Kuiper Belt objects known to date. Moreover, at least one of the belt objects - Eris - is a larger body than Pluto and is 27% heavier. In this regard, the idea arose to no longer consider Pluto as a planet. On August 24, 2006, at the XXVI General Assembly of the International Astronomical Union (IAU), it was decided to henceforth call Pluto not a “planet”, but a “dwarf planet”.
At the conference, a new definition of a planet was developed, according to which planets are considered bodies that revolve around a star (and are not themselves a star), have a hydrostatically equilibrium shape and have “cleared” the area in the area of their orbit from other, smaller objects. Dwarf planets will be considered objects that orbit a star, have a hydrostatically equilibrium shape, but have not “cleared” the nearby space and are not satellites. Planets and dwarf planets are two different classes of objects in the Solar System. All other objects orbiting the Sun that are not satellites will be called small bodies of the Solar System.
Thus, since 2006, there have been eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The International Astronomical Union officially recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris.
On June 11, 2008, the IAU announced the introduction of the concept of "plutoid". It was decided to call celestial bodies revolving around the Sun in an orbit whose radius is greater than the radius of Neptune’s orbit, whose mass is sufficient for gravitational forces to give them an almost spherical shape, and which do not clear the space around their orbit (that is, many small objects revolve around them) ).
Since it is still difficult to determine the shape and thus the relationship to the class of dwarf planets for such distant objects as plutoids, scientists recommended temporarily classifying all objects whose absolute asteroid magnitude (brilliance from a distance of one astronomical unit) is brighter than +1 as plutoids. If it later turns out that an object classified as a plutoid is not a dwarf planet, it will be deprived of this status, although the assigned name will be retained. The dwarf planets Pluto and Eris were classified as plutoids. In July 2008, Makemake was included in this category. On September 17, 2008, Haumea was added to the list.
The material was prepared based on information from open sources