The centuries-old search for the boundaries of the solar system has repeatedly redrawn the harmonious picture of the universe, forcing scientists to offer new hypotheses as to why the sun has so many satellites and planets. First, astronomers discovered that in addition to large planets, there are thousands of small cosmic bodies in the solar system. They form an asteroid belt located inside Jupiter's orbit. Then Pluto, Sedna, Orc, Kvaoar, Varuna and many other objects orbiting the Sun at distances tens and hundreds of times greater than Jupiter were discovered.
The so-called Kuiper belt, in which the above-mentioned celestial bodies are located, discovered at the end of the 20th century, destroyed the existing system of views, as a result, a number of astronomers even proposed to deprive Pluto of the planetary status. Remember, recently we discussed the controversy about Pluto: is it a planet, a dwarf planet or a double planet?
Let's remember the history of these discoveries …
Planets are celestial bodies that revolve around the Sun, have sufficient weight and size, a spherical shape, and are able to clear their orbit of small cosmic bodies. In 2006, members of the International Astronomical Union decided that there are eight planets in the solar system: Venus, Mercury, Earth, Jupiter, Mars, Saturn, Neptune and Uranus.
In contrast to this concept, there is the term "dwarf planet", which is understood as a celestial body, which also revolves around the Sun, has weight and shape in order to take the shape of a ball, but is not able to clear its orbit and is not a satellite.
Scientists, after the research, came to the conclusion that in ancient times, in the early stages of the existence of the solar system, dwarf planets existed in it. The first objects of the system were formed a little more than 4.5 billion years ago from a gas and dust cloud. Then, for the first three million years, small objects revolved around the sun, colliding with each other and collapsing. The remains of these objects today are presented in the form of ancient asteroids.
An international team of research scientists used a supersensitive magnetometer to study samples of ancient meteorites. Scientists have established the origin of the magnetic field of these objects: as it turned out, it arose as a result of magnetization in a more powerful field. From all this, we can conclude that the first bodies of the solar system, under the outer shell, had a hot metal core, because it is the liquid metal in motion that creates the planet's magnetic field.
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The first objects were approximately 160 kilometers in diameter. Thus, in order for a magnetic field to appear sufficient to magnetize the minerals of the outer layer, the metal had to move quite rapidly. That is, it turns out that the ancient planets of the solar system were much more like modern planets than previously thought.
In addition to Pluto, there are many other small dwarf planets in the solar system, which are called asteroids, or minor planets.
The most significant of these small planets is Ceres, with a diameter of 770 kilometers. It is smaller in size than the Moon by as much as the Moon is smaller than planet Earth.
Ceres was discovered on January 1, 1801. Italian astronomer Giuseppe Piazzi discovered a star that was behaving strangely. In the course of research, he discovered that this star moves slowly in relation to other stars. The astronomer concluded that he had discovered a new planet. A little later, the German astronomer and mathematician Karl Gauss calculated the orbit of Ceres. It turned out that it is located between the orbits of Jupiter and Mars, just in the place where another planet should have been. Of course, this was a great victory, because scientists finally managed to find the long-predicted planet.
A year later, in 1802, scientists were even more surprised when an astronomer from Germany Heinrich Olbers discovered the planet Pallada at about the same place. Two years later, another planet was discovered - Juno, and in 1807 - Vesta. Then, for forty years, scientists did not manage to find new space objects, and only in 1845 the planet Astrea was discovered, and in 1847 - Hebe, Iris and Flora. By the end of the century, scientists had discovered about four hundred minor planets.
In 1920, scientists discovered the asteroid Hidalgo, which moves through Jupiter's orbit and passes relatively close to Saturn's orbit. This asteroid is also notable for the fact that the only one of all the known planets has a very elongated orbit, which is inclined to the plane of the Earth's orbit at an angle of 43 degrees. This small planet was named after the famous hero of the Mexican revolution Gidalgo y Castilla, who died in 1811.
In 1936, the zone of dwarf planets was replenished with new objects. Then the asteroid Adonis was discovered. The peculiarity of this small planet was that it moves away from the Sun at the most distant point at the distance of Jupiter, and at the closest point it approaches the orbit of Mercury.
In 1949, Icarus was also discovered, a minor planet, which is removed from the Sun at its maximum point at a distance equal to two radii of the earth's orbit. The minimum distance of a planet is equal to one fifth of the distance from our planet to the Sun. It is noteworthy that none of the known planets approaches the Sun at such a close distance. As a matter of fact, hence the name (remember the legend of Icarus).
Scientists estimate that there are currently about 40-50 thousand minor planets in the solar system. But of all this set, only a small part can be explored with the help of astronomical instruments.
If we talk about the sizes of small planets, then they are quite diverse. There are few planets that are approximately equal in size to Pallas or Ceres (they reach about 490 kilometers in diameter). Approximately seventy planets have a diameter of about 100 kilometers. Most dwarfs are 20-40 kilometers across, but there are some that are about 2-3 kilometers in diameter. Despite the fact that far from all asteroids have been discovered and investigated, we can already say that their total mass is about one thousandth of the Earth's mass. But this is only for now, because, as scientists believe, currently no more than five percent of the total number of asteroids that are available for research with modern equipment have been discovered.
Of course, one can assume that the physical features of asteroids are about the same, but in fact, scientists are faced with a great variety. In particular, during the study of the reflectivity of asteroids, it was found that Pallas and Ceres reflect light like terrestrial rocks, Juno - like light rocks, and Vesta reflects light like white clouds. This is very interesting, because asteroids are so small that they are not able to keep the atmosphere around them. Thus, asteroids lack an atmosphere and their reflectivity depends directly on the materials that make up the surface of these planets. And yet - in some cases, there is a fluctuation in brightness, which may indicate that these planets have an irregular shape and rotate around their axis.
By the end of the last century, astronomers had discovered about 20 thousand minor planets or asteroids. All in all, astronomers read, there are about a million asteroids in space, the size of which exceeds one kilometer, and which may be of interest to science.
Three kinds of planets
The great planetographic discovery - the discovery of the outer belt of asteroids located beyond the orbit of Neptune - significantly changed the idea of the solar system. On the scale of our planet, such an event would correspond to the discovery of a previously unknown continent. There was a new look at the structure of the planetary system, which until then seemed not quite harmonious, since it had a "strange" planet - the farthest, ninth in a row from the Sun, Pluto. It did not fit into the regular alternation of the eight previous planets. The four planets closest to the Sun (Mercury, Venus, Earth and Mars) belong to the so-called terrestrial type - they are relatively small, but "heavy", composed mainly of rock, and some even have an iron core. The next four planets (Jupiter, Saturn,Uranus and Neptune) are called giant planets - they are very large, several times larger than the Earth, and "light", consisting mainly of gases. Even further away is Pluto, which is not like the planets of the first and second groups. It is much smaller than the Moon and consists mainly of ice. Pluto also differs in the nature of its motion: if the first eight planets move around the Sun in almost circular orbits located in the same plane, then this planet has a very elongated and strongly inclined orbit.if the first eight planets move around the Sun in almost circular orbits located in the same plane, then this planet's orbit is very elongated and strongly inclined.if the first eight planets move around the sun in almost circular orbits located in the same plane, then this planet's orbit is very elongated and strongly inclined.
So Pluto would have been an "outcast" of the solar system, if in the last five years a worthy company had not picked up for him: a completely new, third, type of planetary bodies - ice planetoids. As a result, it became just one of the objects in the outer asteroid belt. Thus, the inner, or main, asteroid belt, located between Mars and Jupiter, ceased to be a unique formation and it has an “ice brother”, the so-called Kuiper belt. Such a structure of the solar system is in good agreement with modern ideas about the formation of planets from a protoplanetary cloud of matter. In the hottest region near the Sun, refractory materials remained - metals and rocks, from which terrestrial planets were formed. The gases escaped to a cooler, more remote area, where they condensed into giant planets. Part of the gaseswhich turned out to be at the very edge, in the coldest region, turned into ice, forming many tiny planetoids, since there was little substance on the outskirts of the protoplanetary cloud. In addition to the planets, comets were formed from this cloud, whose trajectories penetrate all three regions, as well as satellites orbiting the planets, cosmic dust and small stones - fragments of asteroids that plow airless space and sometimes fall to Earth in the form of meteorites.plowing airless space and sometimes falling to the Earth in the form of meteorites.plowing airless space and sometimes falling to the Earth in the form of meteorites.
Ice belt
In 1930, when Pluto was discovered, the orbit of this planet began to be considered the boundary of the solar system, since only vagrant comets fly out of it. Pluto was believed to carry out its border service all alone. This was thought until 1992, when the asteroid 1992 QB1 was discovered beyond the orbit of Pluto, but not too far from it. This event was the beginning of subsequent discoveries. The creation of new powerful telescopes on Earth and the launch of several space telescopes contributed to the identification of many small objects on the outskirts of the solar system that had not previously been possible to see. The "Impact Five-Year Plan" was the period from 1999 to 2003, during which about 800 previously unknown asteroids were discovered. It became apparent that Pluto has a huge family of thousands of small celestial bodies.
The outer asteroid belt, located beyond the orbit of Neptune, is most often called the Kuiper belt after the American astronomer Gerard Peter Kuiper (1905-1973), who studied the Moon and planets in the solar system. However, the assignment of its name to the outer asteroid belt looks very strange. The fact is that Kuiper just believed that all small planets, if any were ever near Pluto's orbit, should have moved to very distant regions, and the space immediately adjacent to Pluto should be free of cosmic bodies. As for the assumption of the existence of numerous small icy asteroids beyond the orbit of Neptune (indistinguishable in telescopes of that time), it was repeatedly expressed from 1930 to 1980 by other astronomers - Americans Leonard and Whipple, Irish Edgeworth, Uruguayan Fernandez. Nevertheless, the name of Kuiper, who denied the very possibility of its existence, somehow firmly "stuck" to this asteroid belt. The International Astronomical Union recommends calling the asteroids of the outer belt simply trans-Neptunian objects, that is, located beyond the orbit of the eighth planet - Neptune. This designation corresponds to the geography of the solar system and has nothing to do with any scientific hypotheses of the past. This designation corresponds to the geography of the solar system and has nothing to do with any scientific hypotheses of the past. This designation corresponds to the geography of the solar system and has nothing to do with any scientific hypotheses of the past.
Kuiper inhabitants
About 1,000 Kuiper belt asteroids are now known, most of which are several hundred kilometers across, and ten of the largest have a diameter of more than 1,000 kilometers. Nevertheless, the total mass of these bodies is small - if one ball is “blind” of them, then it will be equal in volume to 2/3 of the Moon. Small satellites revolve around 14 asteroids. It is assumed that there are about 500 thousand asteroids in the Kuiper belt with a size of more than 30 km. In area, the Kuiper belt is one and a half times larger than that part of the solar system around which it is located, that is, limited by the orbit of Neptune. It is not yet known what the asteroids in the Kuiper belt are made of, but it is clear that ice of various types (water, nitrogen, methane, ammonia, methanol - alcohol, carbon dioxide - "dry ice", etc.) should play the main role in their structure.because the temperature in this region extremely far from the Sun is very low. In such a natural “freezer”, the substance from which the planets of the solar system were formed in the distant past could remain unchanged.
More than 90% of new objects move in almost circular "classical" orbits located at distances from 30 to 50 astronomical units from the Sun. Many of the orbits are strongly inclined to the plane of the solar system, 20 asteroids have an inclination exceeding 40 °, and in some it even reaches 90 °. Therefore, the outlines of the Kuiper belt look like a thick donut, within which thousands of small celestial bodies move. The outer boundary of the belt is at a distance of 47 AU. That is, from the Sun it is expressed very sharply, so there was an assumption about the presence there of a rather large planetary object, possibly even the size of Mars (that is, half the size of the Earth), whose gravitational effect does not allow the asteroids to "disperse". The search for this hypothetical planet is now underway. However, the outer boundary of the belt does not serve as an insurmountable barrier,and 43 asteroids (4% of their known number) go beyond its limits into an area of almost absolute cold and darkness, following strongly elongated orbits extending over 100 astronomical units (15 billion km) from the Sun.
Year after year, the idea of Pluto's role in the solar system changed, and now it is considered as the leader of the icy dwarf planets of the Kuiper belt. A group of two hundred asteroids, whose orbital arrangement and movement speeds practically coincide with the same characteristics of Pluto, were even singled out into a special family called "plutinos", that is, "plutons".
The outer edge of the Kuiper belt, sharply outlined at a distance of 47 AU. from the Sun, it could well be called the new boundary of the solar system. However, some of the ice asteroids are moving beyond this limit. In addition, there is a magnetic field around the Sun, extending up to about 100 AU. e. This area is called the heliosphere - the sphere of the Sun's magnetic field.
A dwarf planet or a giant asteroid?
Since 1992, the number of asteroids discovered on the outskirts of the solar system has increased and it has gradually become clearer that Pluto is not an independent planet, but only the largest representative of the outer asteroid belt. Thunder struck in 1999, when it was proposed to assign Pluto a serial number, which every asteroid has. There was also a suitable reason - the number of numbered objects was approaching ten thousand, so they wanted to transfer Pluto from planets to asteroids with honor, assigning it the "remarkable" number 10,000. The discussion flared up immediately - some astronomers were for this proposal, others were sharply opposed. As a result, Pluto was temporarily left alone, and the "honorary" number went to the next ordinary asteroid. However, in 2005, discussions about Pluto's status erupted with renewed vigor. The discovery of another asteroid in the Kuiper belt at the Palomar Observatory in the United States added fuel to the fire. This object, which was given the designation 2003 UB313, was not ordinary, but rather large. It is now considered most likely that the new object has a diameter of 2,800 km, while Pluto is 2,390 km. However, the data on the new asteroid has yet to be refined in more reliable ways. For example, wait until it passes against the background of a distant star and obscures its light. By the time between the disappearance and appearance of the star, it will be possible to know the diameter of the asteroid very accurately. True, such astronomical events rarely happen, and all that remains is to wait for the right moment.turned out to be not an ordinary, but rather large. It is now considered the most likely that the new object is 2,800 km across, while Pluto is 2,390 km across. However, the data on the new asteroid has yet to be refined in more reliable ways. For example, wait until it passes against the background of a distant star and obscures its light. By the time between the disappearance and appearance of the star, it will be possible to know the diameter of the asteroid very accurately. True, such astronomical events rarely happen, and all that remains is to wait for the right moment.turned out to be not an ordinary, but rather large. It is now considered the most likely that the new object is 2,800 km across, while Pluto is 2,390 km across. However, the data on the new asteroid has yet to be refined in more reliable ways. For example, wait until it passes against the background of a distant star and obscures its light. By the time between the disappearance and appearance of the star, it will be possible to know the diameter of the asteroid very accurately. True, such astronomical events rarely happen, and all that remains is to wait for the right moment. From the time between the disappearance and appearance of the star, it will be possible to know the diameter of the asteroid very accurately. True, such astronomical events rarely happen, and all that remains is to wait for the right moment. From the time between the disappearance and appearance of the star, it will be possible to know the diameter of the asteroid very accurately. True, such astronomical events rarely happen, and all that remains is to wait for the right moment.
The discoverers said that if a new asteroid is larger than the planet Pluto, then it should also be considered a planet. At the same time, they said that if Pluto had been discovered not in 1930, but now, then the question of its classification would not even have arisen - it would certainly be ranked as an asteroid. However, history is history, and Pluto's belonging to the planets has become not so much an astronomical as a general cultural phenomenon, so the question of transferring Pluto into asteroids is encountering quite strong resistance.
A new large object had to be given its own name, and it was here that the discoverers had a serious difficulty. If it is a planet, then according to the rules of the International Astronomical Union (IAS) and in accordance with tradition, it should receive the name of a deity from classical Greco-Roman mythology, and if it is an asteroid, then it should be called the name of a mythological character associated with the underworld ruled by Pluto … True, Brown's group found a clever way out of this situation, proposing to name the new "giant asteroid" Persephone - the name of Pluto's wife in Greek mythology. This name complies with all the rules. But here a purely bureaucratic obstacle arose: the planets are managed by one IAS working group, and the asteroids by another. The controversy reached such an intensity that a special committee of 19 astronomers from different countries was formed,designed to decide whether or not 2003 UB313 is considered a planet.
The members of this committee have been unable to come to a consensus for several months. In the end, the desperate chairman, British astronomer Ivan Williams (who, by the way, claims his name is typically Welsh, characteristic of a native of Wales), found a simple way out of the impasse, saying that if an agreed conclusion could not be reached soon, then he will not follow a scientific path, but will hold the most ordinary vote, and the issue will be decided by a simple majority of votes.
The most distant planetoid
The new idea of Pluto's belonging not so much to planets as to asteroids has not yet had time to settle, but has already found many adherents. It seemed that harmony was found in the arrangement of the planets, which was not hindered by the presence of the "extra" ninth planet. However, the discoveries of new planetoids continued and on March 15, 2004 led to another disruption of harmony among the planets. On this day, a group of American astronomers, led by Michael Brown, announced that during observations at the high-altitude Palomar Observatory (California) in November 2003, they discovered the farthest object in the solar system. It turned out to be located 90 times farther from the Sun than the Earth, and 3 times farther than the "farthest" planet Pluto. And such a giant distance turned out to be only the part of its orbit closest to the Sun. The diameter of this asteroid is smaller,than Pluto - about 1,500 km. He received the name Sedna after the sea mermaid, the ruler of the cold and dark depths of the northern seas in the myths of the Eskimos (Inuit). Such a character was not chosen by chance - after all, this planetoid "dives" into the darkest and coldest region of the solar system, moving away from the Sun 928 times farther than the Earth, and 19 times - than Pluto. Not a single known asteroid goes that far. Sedna immediately took the place of the "rogue planet" that had previously belonged to Pluto. Its highly elongated orbit has once again violated the established understanding of the solar system.moving away from the Sun 928 times farther than the Earth, and 19 times - than Pluto. Not a single known asteroid goes that far. Sedna immediately took the place of the "rogue planet" that had previously belonged to Pluto. Its highly elongated orbit has once again violated the established understanding of the solar system.moving away from the Sun 928 times farther than the Earth, and 19 times - than Pluto. Not a single known asteroid goes that far. Sedna immediately took the place of the "rogue planet" that had previously belonged to Pluto. Its highly elongated orbit has once again violated the established understanding of the solar system.
It makes one revolution around the Sun in a monstrous time - 10,500 years! This planetoid is no longer considered to be in the Kuiper belt, since even with the closest approach, Sedna is 1.5 times farther from the Sun than the outer boundary of this belt. The asteroid has become a kind of "Pluto of the XXI century" - an object whose role is not clear. It is constantly in complete darkness, and the Sun looks like a small star from its surface. Eternal cold reigns on it. In this case, the planetoid turned out to be painted in a rather intense red color and is inferior in "redness" only to Mars. It is unclear whether Sedna is alone or if there are other planetoids at such a great distance - after all, the capabilities of telescopes allow detecting an object with a similar orbit only during 1% of its revolution around the Sun, when it is on the closest part of its trajectory. For Sedna, such a period lasts about 100 years, and then it goes into a distant region for more than 10,000 years, and there it is impossible to see an object of its size in modern telescopes.