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The solar system is the star system where we are now. It consists of the sun, eight planets (originally there were nine planets because Pluto was excluded from dwarf planets), 66 satellites (originally there were 67, Pluto's satellites were excluded) and countless asteroids, comets and meteorites. The order of planets from the sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Mercury, Venus, Earth and Mars near the sun are called terrestrial planets. Spacecraft have all detected and landed on Mars and Venus, and achieved important results. Their common characteristics are high density (>: 3.0 g/cm3), small volume, slow rotation, few satellites, mainly silicate inside and firm shell. Jupiter, Saturn, Uranus and Neptune, which are far away from the sun, are called woody planets. They all have a thick atmosphere, and their surface features are difficult to understand. Generally speaking, they all have solid cores similar to terrestrial planets. There are more than 1000000 asteroids (that is, irregular small stars composed of rocks) between Mars and Jupiter. It is speculated that they may be formed by fragments of a planet between Mars and Jupiter, or some rock fragments failed to accumulate into a unified planet. Meteorites exist between planets and are made of stone or iron.

All these planets revolve around the sun in elliptical orbits, although it is very close to a circle except Mercury. Planetary orbits are more or less in the same plane (called ecliptic plane, based on the orbital plane of the earth). The ecliptic plane is only 7 degrees from the equator of the sun. Pluto's orbit is mostly outside the ecliptic, with an inclination of 17 degrees. The above picture shows the relative size and relationship of each orbit from a specific perspective higher than the ecliptic plane (non-circular phenomenon is obvious). Their orbits run in the same direction (counterclockwise from the north pole of the sun), so scientists exclude Pluto from the nine planets. Except Venus and Uranus, the rotation direction is the same.

The position of the solar system in the universe

The solar system lies at the edge of the Milky Way.

The solar system is a celestial body system, which consists of the sun and celestial bodies orbiting the sun under its gravity. It includes the sun, eight planets and their satellites, asteroids, comets, meteoroids and interplanetary matter. The earth where human beings live is a member of the solar system.

The composition of the solar system

The center of the solar system is the sun. Although it is only a small and medium-sized star, its mass has occupied 99.85% of the total mass of the entire solar system. The rest of the mass includes planets and their satellites, planetary rings and interplanetary matter, such as asteroids, comets, Kuiper Belt objects, outer Neptune objects, theoretical Oort clouds, dust, gas and interplanetary particles. The total surface area of all celestial bodies in the whole solar system is about 65.438+0.7 billion square kilometers. The sun tightly controls all the celestial bodies around itself in the solar system with its strong gravity, making them rotate around themselves in an orderly manner. At the same time, the sun and all the members of the solar system orbit around the center of the galaxy.

So far, eight big planets have been discovered in the solar system. Sometimes they are called "Eight Planets". According to the distance from the sun, these eight planets are: the nearest mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Mercury, Venus, Earth and Mars are also called terrestrial planets, Jupiter and Saturn are also called giant planets, and Uranus and Neptune are also called distant planets. Except for Mercury and Venus, all other planets have satellites. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomers call this area the asteroid belt. In addition, there are more than 1000 comets in the solar system, as well as countless small celestial bodies such as dust, ice masses and debris.

Celestial bodies in the solar system are mainly composed of gases such as hydrogen, helium and neon, ice (water, ammonia and methane) and rocks containing elements such as iron, silicon and magnesium. Some satellites and asteroids of Earth-like planets, Earth, Moon, Mars and Jupiter are mainly composed of rocks. Jupiter and Saturn are mainly composed of hydrogen and helium, and their cores may be rocks or ice.

The origin and evolution of the solar system

It is generally believed that the planetary system is part of the process of star formation, but some scholars believe that it is formed by the close collision of two stars. The most common theory is that the solar system is formed by nebulae.

The basic process of star formation is as follows:

1. The dense core of the nebula becomes too heavy, its center of gravity is unstable, and it begins to split and collapse. Part of the energy of the center of gravity becomes radiated infrared, and the rest increases the temperature of the core. The core of the earth began to be discoid.

2. When the density and temperature trajectory are high enough, deuterium fusion combustion begins, and the outward pressure of radiation slows down (but does not stop) near the collapse of other cores.

3. Other raw materials continue to fall towards this protostar, and their angular momentum may lead to bipolar flow.

Finally, hydrogen begins to melt in the core of the star, and the remaining surrounding materials outside are removed.

The solar nebula hypothesis was put forward by Emmanuel Kant in 1755. He said that the solar nebula rotates slowly and gradually condenses and flattens due to gravity, eventually forming stars and planets. Laplace proposed a similar model in 1796.

The diameter of the solar nebula is about 100AU at first, and its mass is two or three times that of the present sun. In this nebula, heavier substances fall in the middle and pile up into pieces to become future planets. It's getting colder and colder outside the nebula, so the inner planet has a lot of heavy minerals, and the outer planet is gas or ice. Taiyang Yuan was formed about 4.6 billion years ago, and various planets formed in the next 800 million years.

The motion of the solar system

The solar system is a part of the Milky Way. The Milky Way is a spiral galaxy, with a diameter of100000 light-years and more than 200 billion stars. The sun is a typical star in the Milky Way, about 25,000 to 28,000 light years away from the center of the Milky Way. The solar system moves at a speed of about 220 kilometers per second and rotates once in the galaxy with a period of 226 million years.

The eight planets in the solar system all run in nearly circular orbits on almost the same plane and revolve around the sun in the same direction. Except Venus, the rotation direction and revolution direction of other planets are the same.

Comets revolve around the sun in the same direction, mostly in elliptical orbits, and generally have a long period of revolution.

Exploration and study of the solar system

From 65438 to 0959, human beings have been exploring space and studying the solar system through space probes because of their understanding of human living environment and the increasing shortage of earth resources. At present, the detection of the moon and Mars and the detection of asteroids and comets are the main methods.

The long-term study of the solar system has led to the differentiation of several disciplines:

* solar system chemistry:

An important branch of space chemistry, which studies the chemical composition (including material source, element and isotope abundance), physical and chemical properties, chronology and chemical evolution of celestial bodies in the solar system. The chemistry of the solar system is closely related to its origin.

* solar system physics:

The study of the physical characteristics, chemical composition and cosmic environment of planets, satellites, asteroids, comets, meteors and interplanetary substances in the solar system.

* the law of gravity in the solar system;

The law of gravitational interaction between celestial bodies in the solar system.

* the stability of the solar system:

One of the basic problems of celestial evolution and celestial mechanics.

Solar system and other planetary systems

Although scholars agree that there are other celestial systems similar to the solar system, other planetary systems were not discovered until 1992. Up to now, dozens of planetary systems have been discovered, but the detailed information is still scarce. The discovery of these planetary systems depends on the Doppler effect. By observing the periodic change of the star spectrum, we can analyze the change of the star speed, infer whether there is a planet, and calculate the mass and orbit of the planet. Using this technology, only the large planet of Jupiter can be found, but the planet the size of the earth cannot be found.

In addition, another purpose of studying celestial systems similar to the solar system is to explore whether there is life on other planets.

Some information about the sun and the eight planets

The data in the table below are all relative to the sun: (The number of satellites is as of the end of 2005)

The data comparison table between the sun and the eight planets (the equatorial diameter is 6370 kilometers of the earth's diameter), and the distance and orbital radius are in astronomical units.

Celestial Distance (AU) Equatorial Diameter Mass Orbital Radius (AU)| Orbital Inclination (degrees) | period of revolution (years) | Rotation Period (days) | Number of satellites discovered.

Sun 0 109 333400-27.275-

Mercury 0.39 0.382 0.05528 0.3810 7.0050 0.24552 58.60

Venus 0.720.949 0.820.723.40.615 243.0185 (inversion) 0

Earth1.001.001.001.001.000 0.99731.

Mars1.50.53 0.1.521.91.881.0260 2

Jupiter 5.211.23185.201.311.860.413563.

Saturn 9.59.4195 9.54 2.5 29.46 0.444 47 (34 have been named)

Uranus19.23.9814.619.220.84.010.718329

Neptune 30.13.8117.230.061.8164.790+0313.

1930, Pluto was officially recognized as a planet by the international astronomical union, but some astronomers are still skeptical about its planetary identity.

According to the resolution of the General Assembly of the International Astronomical Union on August 24, 2006, Pluto is regarded as a "dwarf planet" in the solar system and is no longer regarded as a planet.

The ninth planet in the solar system.

At the end of 19, many astronomers speculated that there were other planets besides Neptune, because Neptune's orbit was different from the theoretical calculation. They call this star "Planet X", which means unknown planet.

American astronomer percival Lowell searched for planets other than Neptune twice in 1909 and 19 13, but failed to find them. After 19 15, Lowell published a paper and wrote down the estimated planetary data. In fact, in that year, his observatory took photos of Pluto, but it was not until 1930 that he admitted that it was a planet.

But the mass of Pluto is too small to explain Neptune's orbit. Astronomers continue to search for "planet X", but this name has the meaning of the tenth largest planet, because X means 10 in Latin. It was not until Voyager 2 approached Neptune that it was discovered that the mass of Neptune had been miscalculated a lot. Under the influence of the correct mass and Pluto, Neptune's actual orbit is consistent with its calculated orbit.

According to the calculation of planetary orbits, a planet about the size of the earth can't be within 60AU (Pluto is now about 30AU from the sun). If there is a tenth planet, its orbit will be very inclined. It is likely that celestial bodies in other galaxies are too close to the sun and are attracted to the orbit by the sun.

The status of Pluto has always been controversial in astronomy. Even planetariums in some places have excluded Pluto from the status of the nine planets.

According to the resolution of the General Assembly of the International Astronomical Union on August 24, 2006, Pluto is regarded as a "dwarf planet" in the solar system and is no longer regarded as a planet.

Since 2 1 century, scientists have discovered three larger planets in the farther periphery of Pluto. This sequence is "Sedna" discovered in 2004, and its code name is 2003 VB12. In 2005, "Santa Claus" was published at the same time, with code number 2003 EL6 1 and code number 2003 UB3 13 (its name was not announced by the discoverer).

On July 9, 2005, American scientists discovered 2003 UB3 13. Researchers estimate that it is 3000 kilometers in diameter, and some people think it may be the tenth largest planet in the solar system. However, in 2006, the General Assembly of the International Astronomical Union decided to list it as a dwarf planet.

"Water Planet"

Astronomers have found that Mercury, the nearest to the sun, has some unexplained tiny movements. Astronomers suspect that it may be caused by the gravity of a planet closer to the sun than Mercury, and named this planet as "Zhu Rong Star" after a Vulcan (usually translated as "Vulcan Star" in Chinese), but astronomers have not found this planet after more than 50 years of observation.

Einstein's general theory of relativity has ruled out the hypothesis that there are planets in water. The gravitational theory of general relativity explains the strange motion of Mercury, but astronomers have not given up their search for "water planets".

Other information

There are many celestial bodies in the solar system with solid surfaces and diameters exceeding 1 km, and their total surface area reaches1700 million square kilometers.

Some people think that the sun is actually the main star of a binary system, and there is a companion star named "Nemesis" in a distant place. This hypothesis is used to explain the regularity of species extinction on earth. It is believed that its companion star will disturb the asteroids and comets in the system, make them change their orbits and rush into the solar system, increase the probability of hitting the earth, and cause periodic mass extinction.

The formation of planets

Earthlike planets are formed by solid particles colliding and gathering into tiny planets, and then gathering tiny planets.

Woodlike planets begin with the mutual adsorption of water and ice. When the mass is large enough, they further adsorb hydrogen and methane to form gas planets.

Planets in the solar system can be roughly divided into two categories: terrestrial planets and woody planets.

terrestrial planet

Members include Mercury, Venus, Earth and Mars. It is a small and dense rock world with relatively scarce atmosphere. Internal structure: there is a metal core in the center, surrounded by a stone shell, and there are quite a few holes on the surface, with an average density of about 3-5g/cm3.

Jovian planet

Members include Jupiter, Saturn, Uranus and Neptune. It is a gas world with large volume and mass, but low density and dense atmosphere. The average density is about ≤ 1.75 g/cm3, the density of Saturn is about 0.7g/cm3, and the mass of Jupiter is about 3 18 times that of the earth. Structure: Rock core, liquid metal hydrogen and liquid molecular hydrogen from inside to outside, with gas-filled atmosphere in the center and swirling clouds on the surface. In addition, there are planetary rings and eight planets around the solar system, with the sun as the center: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Who is the farthest planet in the solar system?

Since1February 1999 1 1, Pluto has finally become the farthest planet in the solar system. According to the calculation of JPL astronomers, Pluto will be the farthest planet from the sun in 228 years from 9:08 am Universal Time (UT) (Central Plains Standard Time 17:08).

On February 1930, Clyde Tombaugh discovered Pluto while studying the sky photos taken by the telescope of Lowell Observatory. Pluto's cycle around the sun is 248 years, its orbital inclination is about 17 degrees, and its orbital eccentricity is about 0.2480. It is mainly composed of rocks and ice with four distinct seasons. Pluto has only one satellite, Ka Rong, which was discovered in 1978. Because the inclination and eccentricity of Pluto's orbit are much larger than those of other planets, that is to say, some orbits near Pluto's perihelion will fall inside Neptune's orbit, so in the 20 years from February 7, 1979 to February 7, 1979, Pluto was closer to the sun than Neptune.

So will Pluto collide with Neptune in February 1 1? The answer is: no! Why? If Pluto and Neptune want to collide, they must reach the intersection of their orbits at the same time. The rendezvous period between Pluto and Neptune is about 497 years, that is, Pluto orbits the sun twice and Neptune orbits the sun three times. So whenever Pluto passes through the intersection of orbits, Neptune will always go around somewhere else, and the chance of collision is very small. In addition, Pluto's orbital inclination relative to the ecliptic plane is much larger than that of other planets, which is one of the reasons why there will be no collision.

Pluto is about 2300 kilometers in diameter. Of all the planets, it is much smaller than terrestrial planets (water, gold, earth and fire), even smaller than the moon. Its nature is different from that of giant gaseous woody planets (wood, earth, heavenly king, Neptune). The orbital inclination and eccentricity are also much larger than those of other planets. Therefore, some astronomers believe that Pluto should not belong to the "planet" family, but should belong to the "Kuiper Belt". The Kuiper Belt lies outside the orbits of Neptune and Pluto. The celestial bodies in the belt are much smaller than Pluto, and most of them are made of ice, which may be fragments of the early evolution of the solar system. But Pluto's shape is spherical and irregular, which is slightly different from these copper belt objects; Moreover, Pluto revolves around the sun regularly, so after many controversies, it is still classified as a "planet" family. 2006-08-24 The General Assembly of the International Astronomical Union decided that Pluto is regarded as a "dwarf planet" in the solar system and is no longer regarded as a planet.

So our understanding of Pluto is very limited. The Jet Propulsion Laboratory (JPL) led by NASA is currently carrying out a project called Pluto? According to the plan of "Pluto-Kuiper Express", it is predicted that the spacecraft will be launched in 2004, and about 10 years later, the spacecraft will fly over Pluto and Chalong to detect celestial bodies in the Cooper Belt.

According to the resolution of the General Assembly of the International Astronomical Union on August 24, 2006, Pluto is regarded as a "dwarf planet" in the solar system and is no longer regarded as a planet. From this day on, Pluto is no longer the farthest planet in the solar system, and Neptune has taken its place.

Mercury's little file:

The daily average distance is 579 10000km(0.38 AU).

4,878 kilometers in diameter

Mass 3.30e23

The density is 5.43g/cm.

Gravity 0.376 g

Rotate 87.97 Earth Days.

Rotate 58.65 earth days.

Mercury is the closest planet to the sun. Because it is too close to the sun, the surface temperature is very high, so the spacecraft is not easy to approach, and it is not easy to observe on the earth. Because the observable time is concentrated in a few minutes before the sun comes out in the morning and a few minutes after sunset, it is not easy to grasp the time. And in the case of Shang Gao background brightness, it is not easy to find a mercury that is not much bigger than the moon. Mercury is the closest planet to the sun. Mercury is small and made of rocks. Its surface is covered with craters and potholes formed by meteor impact, and there are smooth and sparse potholes plains. Mercury also has ridges on its surface, which were formed by the gradual cooling and contraction of the planet's core 4 billion years ago, so its surface is uneven. Mercury's rotation speed is very slow, with a rotation of nearly 59 Earth days, so one solar day of Mercury (from sunrise to another sunrise) is almost 176 Earth days-twice that of Mercury's 88 days a year. Mercury's surface temperature varies greatly, reaching 430 degrees Celsius on the sunny side and-170 degrees Celsius on the dark side. When night falls, the temperature drops rapidly because Mercury has almost no atmosphere. The atmospheric composition includes traces of helium and hydrogen captured by the solar wind, and perhaps a little other gases.

Venus's little file:

Average daily distance108,200,000 km (0.72 au).

Diameter 12,103.6km.

Mass 4.869e24

The density is 5.24 g/cm.

Gravity 0.903 g

Rotate 224.7 Earth Days

Rotate 243 earth days

Venus is the second planet in the solar system. The brightest planet in the whole day is Venus, which is usually seen in the morning or evening. At the brightest time, the brightness can exceed -4, just like a street lamp hanging on the hillside, which can be observed by ordinary telescopes, and the profit and loss phenomenon like the moon can often be seen. In the ancient western world, Venus represented the beautiful goddess. Venus is a planet made of rocks and the second farthest planet from the sun. Venus rotates slowly in the opposite direction while revolving around the sun, so its rotation period is the longest in the solar system, which takes about 243 Earth days.

Venus is slightly smaller than the earth, and its internal structure may be similar. Venus is the brightest celestial body in the sky except the sun and the moon, because its atmosphere can strongly reflect sunlight. The main component of the atmosphere is carbon dioxide, which can absorb more heat under the greenhouse effect. Therefore, Venus has become the hottest planet with a surface temperature of 480 degrees Celsius. Thick clouds contain sulfuric acid droplets, which are blown to the earth by the wind at a speed of nearly 360 kilometers per hour. Although Venus takes 243 earth days to rotate once, it only takes 4 earth days for high-speed wind to blow clouds around the planet once. High temperature, acid rain and extremely high atmospheric pressure (about 90 times of the earth's surface) indicate that Venus's environment is harsh.

Earth small file:

Average daily distance149,600,000 km (1.00au).

Diameter12756.3km.

The mass is 5.976e24kg.

The density is 5.52g/cm.

Gravity 1 g (9.8m/s2)

Rotate 365.26 Earth Days

Earth rotation 1 day

The beautiful earth, the miracle of life, is it a coincidence of the universe or a masterpiece of God? The earth is the third planet in the solar system, and there is a satellite called the moon. The protection of the earth's atmosphere and a proper distance from the sun are important conditions for the origin of life.

The earth is the third farthest planet from the sun, the largest diameter and the largest proportion of rocky planet, and the only planet known to have life. The rocks and metals inside the earth show that it is a typical plate. Because the plates are pushed, earthquakes and volcanoes will occur at the junction. The earth's atmosphere and the same protective layer can block harmful radiation from the sun and prevent meteors from hitting the earth's surface. In addition, it can accumulate enough heat to prevent the temperature from dropping sharply. Seventy percent of the earth's surface is surrounded by water, which has not been found on the surface of other planets. The earth has a natural satellite-the moon, which is large enough to regard these two celestial bodies as a two-planet system.

Small files of Mars:

The daily average distance is 227,940,000 km (1.52 au).

6794 kilometers in diameter

Mass 6.4219e23kg

The density is 3.94 g/cm.

Gravity 0.38 g

Rotate 686.98 Earth Days.

Earth rotation 1.026 days

Mars is the fourth planet in the solar system. In the clear night sky, Mars, representing the god of war, shines with fire, attracting the attention of thousands of people in ancient and modern times. One hundred thousand years ago, a rock from Mars fell into the polar region of the earth and was frozen. What people found in this meteorite may be the trace fossils left by life. This fossil was formed on Mars 3 billion years ago. Scientists are actively studying and exploring this planet with mysterious rivers and volcanoes on its surface. Is there life on Mars?

Mars is usually called the red planet. Mars is the third smallest planet in the solar system, with a diameter of about half of that of the Earth, a volume of about one tenth of that of the Earth, and a surface gravity of about one third of that of the Earth. The atmosphere of Mars is thinner than that of the earth, only 1% of the earth's atmosphere, and the main component is carbon dioxide. There are also some clouds and morning fog. Because the atmosphere is very thin, there is no greenhouse effect on Mars. The temperature near the equator of Mars can reach 27C during the day and drop to-110c at night.

There are many great plains formed by the solidification of volcanic lava in the northern hemisphere of Mars, many craters and large impact basins in the southern hemisphere, several large extinct volcanoes, such as Mount Olympus, which is 600 kilometers wide, and many canyons and bifurcated riverbeds. Canyon is caused by crustal movement, and riverbed is generally considered to be formed by dry rivers. In the high latitudes of Mars, due to the low temperature in winter, carbon dioxide in the atmosphere will freeze, form clouds at a height of 50 kilometers, and disappear in spring. In summer, due to strong sunshine and high ground temperature, the atmosphere near the ground is heated to produce strong updraft. This kind of airflow will roll up the dust on the ground, absorb the heat of the sun in the air, further raise the atmospheric temperature and increase the rising speed, so large-scale rockburst sand can often be seen on Mars.

Mount Olympus, the largest volcano on Mars, is 24 kilometers from the ground, almost three times as high as the highest mountain on earth and the highest mountain in the solar system.