How many planets are there in the solar system and what are their names?

1. Inner Solar System

The inner solar system is traditionally the name of the terrestrial planets and asteroid belt region, which is mainly composed of silicates and metals. This region is squeezed close to the sun and has a radius shorter than the distance between Jupiter and Saturn.

Inner Planets All Inner Planets

The four inner planets, or terrestrial planets, are characterized by being dense, rocky, with few or no moons, and no ring systems. They are composed of high melting point minerals, such as silicate minerals, a solid surface crust and a semi-liquid mantle, and a metallic core composed of iron and nickel. Three of the four (Venus, Earth, and Mars) have substantial atmospheres, and all have surface features such as impact craters and geological structures (grabens, volcanoes, etc.). The inner planets are easily confused with the inner planets (Mercury and Venus) that are closer to the sun than Earth. The planets move in one plane and in one direction.

Mercury

Mercury (0.4 AU) is the closest planet to the sun and the smallest planet (0.055 Earth mass). It has no natural satellites, and its only known geological features, apart from impact craters, are wrinkled ridges presumably created during its early history and contraction. Mercury has only a negligible atmosphere, consisting of gas atoms blasted out by the solar wind. The relatively large iron core and thin mantle cannot yet be explained. Hypotheses include a huge impact that stripped off its outer shell, and that solar energy in its youth inhibited the growth of the outer shell.

Venus

Venus (Venus) (0.7 astronomical units) is similar in size to the Earth (0.86 Earth mass), and like the Earth, it is surrounded by a thick silicate mantle At the core, there is also a thick atmosphere and evidence of internal geological activity. However, its atmosphere is 90 times denser than Earth's and very dry, and it has no natural satellites. It is a hot planet, with surface temperatures exceeding 400°C, which is likely caused by the large amount of greenhouse gases in the atmosphere. There is no clear evidence that Venus's geological activity is still ongoing, but the atmosphere without the protection of a magnetic field should be depleted, so it is believed that Venus's atmosphere is replenished through volcanic eruptions.

Earth

Earth (1 AU) is the largest and densest of the inner planets. It is also the only planet with ongoing geological activity and life. It also has hydrospheres and observed plate structures that are unique among Earth-like planets. The Earth's atmosphere is also completely different from other planets. It has been modified by the organisms living here to contain 21% of free oxygen. It has only one satellite, the moon; the moon is also the only large satellite among the terrestrial planets. The Earth's revolution (the sun) takes about 365 days, and its rotation takes about 1 day. (The Sun does not always shine directly at the equator because the Earth is tilted slightly as it orbits the Sun.)

Mars

Mars (1.5 AU) is smaller than Earth and Venus (0.17 Earth mass), with only a thin atmosphere dominated by carbon dioxide. Its surface, such as Olympus Mons, has dense and huge volcanoes, and Mariner Canyon has deep grabens, indicating that there were still violent geological activities not long ago. . Mars has two small natural satellites, Deimos and Phobos, which may be captured asteroids.

Asteroid Belt

Main Belt of Asteroids and Trojan Asteroids Asteroids are the most important members of small bodies in the solar system and are mainly composed of rocks and non-volatile materials.

The main asteroid belt is located between the orbits of Mars and Jupiter, 2.3 to 3.3 astronomical units from the sun. They are considered to be remnants of material that failed to aggregate due to the gravitational disturbance of Jupiter during the formation of the solar system. .

Asteroids range in size from hundreds of kilometers to microns.

Except for the largest Ceres, all asteroids are classified as small celestial bodies in the solar system. However, there are several asteroids, such as Vesta and Hygiea. If they can be confirmed to have reached a state of hydrostatic equilibrium, they may Will be reclassified as a dwarf planet.

The asteroid belt contains tens of thousands, possibly millions, of small objects with a diameter of more than one kilometer. Still, the total mass of the asteroid belt is unlikely to be one thousandth the mass of Earth. Members of the asteroid main belt are still sparse, so no spacecraft accidents have occurred while passing through it.

Small celestial bodies with a diameter of 10 to 10.4 meters are called meteoroids.

Ceres

Ceres (2.77 AU) is the largest celestial body in the main belt and the only dwarf planet in the main belt. Its diameter is nearly 1,000 kilometers, so its own gravity is enough to make it a sphere. When it was discovered in the early 19th century, it was considered a planet. It was reclassified as a minor planet in the 1850s as more small objects were discovered. In 2006, it was reclassified again as a dwarf planet.

Asteroid families

The asteroids in the main belt can be divided into several asteroid groups and asteroid families based on orbital elements. Asteroid moons are small bodies that orbit larger asteroids. Their identification is not as clear-cut as that of planet-orbiting moons, because some are nearly as large as the parent body they orbit.

There are also comets in the main belt, which may be the main source of water on Earth.

The Trojan asteroid is located at Jupiter's L4 or L5 point (the unstable gravitational balance point in front and behind the planet's orbit), but the name "Trojan" is also used for other planets. Or a small body located at a Lagrangian point in a satellite orbit. The Hilda family is a family of asteroids whose orbital period is 2:3* that of Jupiter. When Jupiter orbits the sun twice, this group of asteroids will orbit the sun three times.

The inner solar system also contains many "naughty" asteroids and dust particles, many of which will cross the orbits of the inner planets.

2. Middle Solar System

The central region of the solar system is home to gas giants and their planet-sized satellites. Many short-period comets, including the Centaurs, are also in this region. This region has no traditional name and is occasionally referred to as the "outer solar system", although the outer solar system usually refers to the region beyond Neptune. The main component of the solids in this region is "ice" (water, ammonia and methane), which is different from the inner solar system, which is dominated by rocks.

Outer Planets

All Exoplanets The four outer planets, also known as the Jovian planets, encompass 99% of the known mass surrounding the Sun. The atmospheres of Jupiter and Saturn both contain large amounts of hydrogen and helium, while the atmospheres of Uranus and Neptune contain more "ices" such as water, ammonia and methane. Some astronomers believe that they should be in another category, called the "Uranus family" or "ice giants." All four gas giants have planetary rings, but only Saturn's rings can be easily observed from Earth. The name "exoplanet" is easily confused with "outer planet", which actually refers to the planets outside the orbit of the Earth. In addition to the outer planets, there is also Mars.

Jupiter

Jupiter (5.2 astronomical units) is mainly composed of hydrogen and helium. Its mass is 318 times that of the Earth and 2.5 times that of the other planets combined. Jupiter's abundant internal heat has created some near-permanent features in its atmosphere, such as cloud bands and the Great Red Spot. Jupiter has 63 discovered moons. The four largest ones, Ganymede, Callisto, Io, and Europa, show characteristics similar to those of Earth-like planets, such as volcanism and internal heat. Ganymede is larger than Mercury and is the largest satellite in the solar system.

Saturn

Saturn (9.5 AU) is famous for its obvious ring system. It is very similar to Jupiter, such as the structure of its atmosphere.

Saturn is not very big, with a mass only 95 times that of Earth. It has 60 known moons, Titan and Enceladus, and has huge ice volcanoes that show signs of geological activity. Titan is larger than Mercury and is the only moon in the solar system that actually has an atmosphere.

Uranus

Uranus (19.6 AU) is the lightest outer planet, with a mass 14 times that of the Earth. Its axis of rotation is tilted 90 degrees to the ecliptic, so it orbits the sun lying sideways, which is very unique among planets. Among gas giants, its core has the lowest temperature and radiates very little heat into space. There are 27 known satellites of Uranus, the largest ones being Titania, Oberon, Umberriol, Ariel, and Miranda.

Neptune

Although Neptune (30 astronomical units) looks smaller than Uranus, its higher density means that its mass is still 17 times that of the Earth. Although it radiates more heat, it is far less than Jupiter and Saturn. Neptune has 13 known moons. The largest, Triton, still has active geological activities and has geysers that erupt liquid nitrogen. It is also the only large retrograde moon in the solar system. In the orbit of Neptune, there are some 1:1 orbiting asteroids that vibrate, forming the Neptune Trojan Group.

Comets

Comets are small celestial bodies in the solar system, usually only a few kilometers in diameter, and are mainly composed of volatile ice. Their orbits are highly eccentric, with perihelion generally inside the orbit of the inner planets and aphelion beyond Pluto. When a comet enters the inner solar system, its approach to the sun will cause the material on its icy surface to sublimate and ionize, creating a coma and dragging out a comet tail composed of gas and dust particles that can be seen with the naked eye.

Short-period comets are comets with orbital periods shorter than 200 years, while long-period comets can have orbital periods as long as thousands of years. Short-period comets, like Halley's Comet, are thought to originate from the Kuiper Belt; long-period comets, like Hale-Bopp, are thought to originate from the Oort Cloud. Many groups of comets, such as the Cruz family, may have originated from a collapsed parent body. Some comets have hyperbolic orbits and may come from outside the solar system, but it is difficult to accurately measure these orbits. Comets whose volatile materials have been dispersed by the sun's heat are often classified as asteroids.

Centaurs

Centaurs are celestial bodies scattered in the range of 9 to 30 astronomical units, that is, orbiting between Jupiter and Neptune, similar to comets and mainly composed of ice. . The largest known object in the Centauri group is 10199 Chariklo, with a diameter of 200 to 250 kilometers. The first one to be discovered was 2060 Chiron, which is currently classified as a comet because it produces a coma like a comet when it approaches the sun. Some astronomers classify the Centaurs as discrete objects within the Kuiper Belt and as continuations of the outer discrete disk.

3. Trans-Neptune Region

The region beyond Neptune, usually called the outer solar system or the Trans-Neptune region, is still a vast unexplored space. This area seems to be a world of small celestial bodies in the solar system (the largest is less than one-fifth the diameter of the Earth and has a mass far less than the moon), mainly composed of rock and ice.

Kuiper Belt

The Kuiper Belt, in its original form, is considered to be a ring of debris and debris similar in size to asteroids but mainly composed of ice, spreading in 30 to 50 astronomical units from the sun. This region is thought to be the source of short-period comets such as Halley's Comet. It is mainly composed of small solar system objects, but many of the largest objects in the Kuiper Belt, such as Genesis, Varuna, 2003 EL61, 2005 FY9 and Ergus, may be classified as dwarf planets. It is estimated that there are more than 100,000 objects with diameters greater than 50 kilometers in the Kuiper Belt, but the total mass may be only one-tenth or even one percent of the Earth's mass. Many Kuiper Belt objects have more than two moons, and most orbit outside the ecliptic plane.

The Kuiper Belt can be roughly divided into two parts: the primary vibration belt and the traditional belt. The primary vibration belt is composed of celestial bodies that have a primary vibration relationship with Neptune’s orbit (when Neptune orbits the sun Three times it goes around the sun twice, or Neptune only goes around once when it orbits twice). In fact, Neptune itself is also considered a member of the *** vibration belt. The traditional members are celestial bodies that do not vibrate with Neptune and are scattered in the range of 39.4 to 47.7 astronomical units. Traditional Kuiper Belt objects are named after 1992 QB1, one of the first three discovered objects, and are classified as QB1-like objects.

Pluto and Charon

Pluto and the three known moons It is not yet certain whether Charon should be classified as a moon as currently considered or a dwarf planet. Because the centers of mass of Pluto and Charon's mutual orbits are not beneath the surface of either planet, a Pluto-Charon binary system is formed. Two other very small moons, Nix and Hydra, orbit Pluto and Charon.

Pluto is in the oscillation zone and has a 3:2 oscillation with Neptune (when Pluto orbits the sun twice, Neptune orbits three times). Objects with such orbits in the Kuiper Belt are collectively called Plutoid Objects.

The divergent disk

The divergent disk overlaps with the Kuiper Belt, but extends outward into space. The objects in the discrete disk should have been thrown from the Kuiper Belt into unstable orbits during the early formation of the solar system due to the gravitational disturbance caused by Neptune's outward migration. The perihelion of most ecliptic discrete objects is within the Kuiper Belt, but the aphelion can be as far as 150 astronomical units; the orbits also have a large inclination angle to the ecliptic plane, and some are even perpendicular to the ecliptic plane. Some astronomers believe that the zodiacal discrete objects should be another part of the Kuiper Belt and should be called "Kuiper Belt Discrete Objects".

Eris (also known as Xena)

Eris (136199 Eris) (average distance 68 AU) is the largest known ecliptic discrete object, and what caused it It's a planetary debate. With a diameter at least 15 times larger than Pluto and an estimated 2,400 kilometers (1,500 miles), it is the largest known dwarf planet. Eris has a satellite, Dysnomia, and its orbit has a large eccentricity like Pluto. The perihelion distance is 38.2 AU (about the average distance between Pluto and the Sun), and the aphelion reaches 97.6 AU. Unit, the tilt angle to the ecliptic plane is also very large.

Scientists from the California Institute of Technology discovered this planet at the edge of the solar system in 2003. It was numbered 2003UB313 and was temporarily named Xina. The discovery was not announced to the outside world until July 29, 2005. It is reported that astronomers from various countries denied that it is a major planet at the International Astronomical Union Conference on August 24, 2006.

According to reports, Xena has a diameter of about 1,490 miles, which is seven to seven miles larger than the dwarf planet Pluto at the edge of the solar system. Xena is 9 billion miles away from the sun. This distance is about three times the distance between Pluto and the sun, which is about 97.6 astronomical units. One astronomical unit refers to the distance between the sun and the earth. It takes Xena 560 years to orbit the sun. It is also the farthest star in the solar system that we know of so far, and is the third brightest star in the "Kuiper Belt." It is lower than the surface temperature of Pluto, about minus 214°C, making it a very uninhabitable place.

This star is round and may be up to twice the size of Pluto. He estimated that the diameter of the newly discovered star is estimated to be 2,100 miles, which is 1.5 times that of Pluto.

This star maintains an angle of 45 degrees with the main plane of the solar system, and most other planets orbit in this main plane. That's why it has never been discovered, Brown said.