How many planets are there in the solar system?

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Le soleil et les planètes qui l'entourent

Astronomical knowledge has evolved rapidly in recent years, sometimes leading to the redefinition of already established models. It is even more legitimate to wonder how many planets the solar system has. The solar system is a complex made up of all kinds of celestial bodies, more precisely planets, asteroids and comets, all revolving around the sun, that luminous ball that gives us the pleasant feeling of warmth and light during the summer holidays. Until a few years ago, young students were taught that the solar system had nine planets. However, Pluto lost its ninth planet status in August 2006, following a redefinition of what a planet is. After a vote by the International Astronomical Union, it was downgraded to a dwarf planet. Then we witnessed the discovery of a hypothetical planet that would also orbit the sun: Planet 9. The official planets are therefore eight and can be classified into two higher categories: telluric planets and gas giants. The world of stars, an immeasurable dimension… In astronomy, the universe represents the largest known dimension, to the point that its observable diameter from the earth is estimated at about 45 billion light-years in radius. That corresponds to 450,000 billion billion kilometers, incredible, isn’t it? In this seemingly endless universe there are approximately 2000 billion galaxies. They are gatherings of stars and their possible planets that form this cosmic structure. They contain gas, interstellar dust, and generally have a large black hole at their center. All these massive bodies float there under the effect of gravitation. The Sun, so visibly large, is in fact only one star of the 200,000,000,000 that populate our galaxy. Its composition is a priori hydrogen, helium and also heavy elements, such as carbon, nitrogen and oxygen. The fusion as well as the compression of these elements produce energy. This is how we can see it from earth in the form of heat and light. The central temperature is 12 million degrees Celsius against 5,600 °C on the surface. What exactly is a planet? The exact definition of a planet has caused some divergence of theories and ideas among scientists. To find common ground, astronomers, meeting at the International Astronomical Union (IAU) congress in August 2006, decided by vote to divide the planets and other bodies of the solar system into three categories. 1 – Planets in simple terms: these planets must meet the following conditions: revolve around the Sun; be relatively spherical and in hydrostatic equilibrium; to have eliminated any rival body moving in close orbit (or turn it into one of its satellites, or cause its destruction by impact). They are eight in number to correspond to these criteria: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. 2 – Dwarf planets These are celestial bodies that meet the following conditions: to be in orbit around the sun, to be relatively spherical and in hydrostatic equilibrium, not to have removed any body capable of moving in a close orbit, not to be a satellite. If we take all these criteria into account, there are therefore five dwarf planets in the solar system, including Ceres, Pluto, Eris, Haumea and Makemake. 3 – The small bodies of the solar system They correspond to all other objects in orbit around the Sun, with the exception of satellites, which do not meet the criteria listed above. The main planets of the solar system Some components of our solar system are visible to the naked eye. This is indeed the case of the sun and the moon, but also of some neighboring planets such as Mercury, Venus, Mars, Jupiter and Saturn. There are currently eight main planets that can be classified into two higher categories: telluric planets and gas giants. Telluric planets These are planets that have condensed from heavy elements (silicates and metals). They generally have three concentric envelopes that include the core, mantle, and crust. Its surface is solid and composed mainly of non-volatile materials. There are four of them and they are the planets closest to the sun. 1- Mercury It is the smallest of the planets, measuring approximately 4,878 km in diameter. It is on average 58 million km from the sun, making it the closest. Minerals, fractures and craters cover its surface. Its metallic core is composed of nickel and iron corresponding to 55% of the planet’s mass. It has no satellites and no internal activity. 2- Venus Located 108 million km from the sun, Venus is the second largest of the terrestrial planets since its diameter is 12,100 km. It has the thickest atmosphere of the four terrestrial planets with a ground pressure more than 90 times that of Earth. This yellow atmosphere composed of sulfuric acid, carbon dioxide, sulphur, nitrogen and various other gases has earned it the name “hidden planet”. It has no satellites. Earth Our beloved planet is the third telluric planet. It is about 149 million km from the sun and measures 12,756 km in equatorial diameter. It is the only planet in the solar system that can host living beings and, moreover, the only possessor of liquid water. We have all been able to observe its sublime and only natural satellite: the moon! SEE ALSO: Moon rising sign, what is it? 4- Mars Called the red planet, it is at an average distance of 228 million km from the sun. Its approximate diameter is 6,794 km. In addition, it has two satellites between them: Phobos which measures about 18 km and Déimos which measures 10.4 km in diameter. It is also on Mars that we find Olympus Mons, the most immense volcano in the entire solar system. In fact, it measures 21.2 km high by a base of 624 km wide. The gas giants are planets without a solid surface that formed far from the Sun from lighter elements such as hydrogen, helium, methane and also water ice. 5- Jupiter This is the largest of the planets, located at a distance of 778.4 million km from the sun. It has a colossal size of 14,2800 km so that only its core, in size is comparable to that of the Earth and more than 10 times its mass. Its atmosphere has three distinct cloud layers, namely: the outer part consisting of ammonia track ice clouds, ammonium hydrogen sulfate clouds and the last of water and ice clouds. Violent winds circulate on its surface, among which is a gigantic storm called “the eye of Jupiter”, in particular an oval shape measuring 40,000 km long and 12,000 km wide. The gigantic planet also has 16 satellites. SEE ALSO: What is the largest planet in the solar system? 6- Saturn This is the second largest planet in the solar system. It is about 1.4 billion km from the sun and measures 120.600 km in equatorial diameter. It must be said that it is easily recognizable by the gigantic rings that surround it since these form a disc of 140,000 km in diameter separated into several divisions by dark areas. A rocky core of silicates as well as iron surrounded by a layer of metallic hydrogen. lic. constitutes its internal structure. It also holds the record for the largest number of satellites, estimated at 200, and about 150 smaller moons. the most important are Titan, Rhea, Iapetus, Dione, Thetis, Enceladus, Hyperion, Mimas and Phoebe. 7- Uranus Uranus is 2.9 billion km from the sun, in terms of its diameter, it is 51,300 km. It is a pastel blue ice planet that is mainly composed of hydrogen, helium and even heavy elements like oxygen, carbon, neon, nitrogen, silicon and iron. It has a total of 27 satellites and 13 rings. 8- Neptune It is the most distant planet of all since it is 4,490 million km from the sun. Measuring 49,100 km in diameter at the equator, Neptune also has five rings with widths ranging from approximately 100 km to 5,000 km. It has two major moons called Nereid and Triton, but there are at least 12 more than these. SEE ALSO: Is the Moon a Planet? And why not? “The Man Who Killed Pluto” Clyde W. Tombaugh is the man who discovered Pluto in 1930. After that, Pluto was considered the ninth planet in the solar system before being declassified in 2006. In 1992 , astronomers have found the Kuiper Belt, a vast area of ​​frozen objects that extend beyond the orbit of Neptune. This asteroid belt would contain more than 100,000 objects within 100 km, of which Pluto was the largest representative. Until… Michael E. Brown sees a body called Eris, considerably larger in size than Pluto. The question of including it as the tenth planet arose, but the discoveries were related to the identification of Makemake, Sedna, Ocus and Quaoar. If we accept that Pluto and Eris are planets, then all these objects would fall into the same category and the solar system would encompass at least 110 planets (including the moon and other Kuiper belt bodies). By then it had become clear that astronomers needed a renewed definition. Brown then asked the International Astronomical Union to reformulate the definition of a planet. It was precisely in 2006 when Pluto was officially removed from the list and cataloged among the dwarf planets. Because of this event, Brown received the name “the man who killed Pluto”. A new planet 9ᵉ? At the same time, the discovery of these objects revealed an unexplored clue in the search for a hidden planet. In fact, Mike Brown and his colleague Konstantin Batygin, have suggested in an article the possible existence of an unknown planet five times larger than Earth. It should be noted that it was Sedna’s abnormal behavior that tipped them off. It’s supposed to draw an elliptical path around the sun, but instead it takes a strange path. It goes from about 11 billion km to 135 billion km from the sun, as if something is attracting it, and distorts its orbit. Thus, if we count this hypothetical planet in the list, the number of the solar system is again 9. Sedna did not remain the only disturbed object, 19 other bodies also stretch in the same direction and each of them tilts on its axis. exactly in the same direction. As a result, the two scientists concluded that there is a 99.8% chance that these disturbances are external in nature. Thus, if one counted this hypothetical planet in the list, the number of the solar system returns to 9.
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