How many planets are there in the solar system?

There are nine planets in the solar system. They are Jupiter, Saturn, Mercury, Venus, Mars, Earth, Uranus, Neptune and Pluto.

Mercury: Mercury is the closest planet to the sun among the nine planets. In ancient China, it was called a star. Westerners call it mercury, which is the messenger of the gods in Roman mythology. Mercury is worthy of the title of messenger: it is the fastest moving planet in the solar system. The average speed of Mercury's revolution is 48 kilometers per second, and that of period of revolution is about 88 days.

Because mercury is too close to the sun and small, it is difficult for people to see it at ordinary times. The surface of mercury is very similar to the moon. It was covered with craters of all sizes. Mercury's atmosphere is extremely thin, and the temperature difference between day and night is very large. During the day, the surface temperature can reach more than 427 degrees, and the minimum temperature at night can be reduced to about-173 degrees.

Mercury has a radius of 2,440 kilometers, which is 38.3% of that of radius of the earth. Mercury is 5.62% of the earth's volume and 0.05 times of the earth's mass. Mercury looks like the moon, but it looks like the earth inside, and it is also divided into three layers: shell, mantle and core. Astronomers speculate that mercury's shell is made of silicate and its center has an iron core larger than the moon.

Mercury's rotation period is 58.646 days, and its rotation direction is the same as its revolution direction. Because the rotation period is very close to that of period of revolution, a day and night on Mercury is much longer than one rotation of Mercury. Its day and night are 176 days for us, 88 days in the day and 88 days in the night.

Mercury has no satellites, so the night of Mercury is lonely. There is no moon there. Besides the sun, the brightest star in the sky is Venus.

Venus: Venus is the second farthest planet from the sun and the brightest star in the sky. Its maximum brightness is -4.4, which is 14 times brighter than the famous Sirius. Venus is a galaxy on the earth, so it is sometimes the morning star and sometimes the evening star. Venus has not been found to have satellites. Because Venus and Earth are very similar in size, mass, density and weight, and Venus and Earth are almost all formed by the same nebula at the same time, astrologers regard them as sister planets. However, not long ago, scientists discovered that Venus is actually very different from the Earth. There is no ocean on Venus. It is surrounded by a thick atmosphere, the main component of which is carbon dioxide, and there is no water at all. Its cloud is made up of sulfuric acid drops. On the surface, its atmospheric pressure is 92 times of the earth's sea level.

Because Venus appeared in the sky in the morning and evening respectively, it was called Taibai or Taibai Venus in ancient China, Qi Ming in the morning star and Chang Gung Memorial in China history books. Ancient astrologers always thought that there were two such planets, so they were called "morning star" and "evening star" respectively. In English, Venus is the ancient Roman god of love and beauty. It has been shrouded in a mysterious veil by curly clouds.

Due to the "greenhouse effect" caused by Venus' thick carbon dioxide atmosphere, the surface temperature of Venus is as high as 482℃, and sunlight heats the surface of Venus through the atmosphere. The heat on the earth's surface is blocked by the atmosphere in the process of outward radiation and cannot be radiated to outer space. This makes Venus hotter than Mercury. A day on Venus is equivalent to 243 days on Earth, which is longer than 225 days in a year. Venus rotates from east to west, which means that on Venus, the sun rises in the west and sets in the east.

The surface of Venus is randomly covered with many small craters. Because Venus has a thick atmosphere, craters with a diameter of less than 2 kilometers can hardly be preserved. However, when large meteorites hit the surface of Venus before the formation of small craters, the fragments they produced produced produced a group of special craters on the surface. There are many volcanoes and volcanic activities on the surface of Venus. At least 85% of Venus is covered by volcanic rocks. A large number of lava flows through hundreds of kilometers, filling the lowlands and forming a vast plain. In addition to hundreds of large volcanoes, more than 100000 small craters dot the surface of Venus. The lava flow from the volcano has produced long ditches, covering hundreds of kilometers, one of which is more than 7000 kilometers.

Earth: The earth was formed 4.6 billion years ago, about 65.438+0.6 billion years ago. The earth only had 9 hours every day and night, much faster than now, about 800 days a year; By 600 million years ago, day and night were extended to 20 hours, and a year was shortened to 440 days. The earth has gradually slowed down its rotation speed, which may be mainly due to the tidal gravity of the moon. It is generally believed that the formation of the earth originated from the differentiation of the solar nebula. In the past 4.6 billion years, the earth has evolved from a uniform sphere to the present "circular" structure. The average crust thickness is 17 km, the mantle thickness is about 3473 km, accounting for 83.4% of the earth's volume, the mantle temperature is 1000 ~ 3000 degrees Celsius, the core thickness is about 3473 km, accounting for 16.3% of the earth's volume, the matter is in liquid state, and the core temperature is as high as 6000 degrees Celsius.

From our point of view on earth, our planet is very huge and rich, surrounded by seemingly endless air; However, from the astronaut's point of view, the earth is just a thin sphere, surrounded by a thin atmosphere, which seems to blow away. For a space traveler, the earth, blue sea, brown or green land and white clouds in the deep and dark space are extremely eye-catching.

The earth is the third farthest planet from the sun, with a distance of 65.438+0.5 billion kilometers (93.2 million miles). The earth's orbit around the sun is 365.256 earth days, and its rotation is 23.9345 hours. The diameter of the earth is 12756 km (7973 miles), which is only a few hundred kilometers larger than Venus. Our atmosphere is composed of 78% nitrogen, 2 1% oxygen and 1% other components.

The earth is the only planet in the solar system where life has settled. Its fast rotation and hot nickel-iron core generate enough magnetic field to cooperate with the atmosphere and protect us from the radiation of the sun and other planets. The atmosphere also protects us from meteors, most of which burn before they reach the earth's surface.

We have learned more about our planet from the results of many interstellar trips. America's first artificial satellite "Explorer 1" discovered the intense radiation zone now called "Van Allen radiation belt", which consists of fast-moving electrons captured by the equatorial annular geomagnetic field. Information from other satellites shows that the geomagnetic field is distorted into the shape of water droplets due to the solar wind. We also know that the thin upper atmosphere, which was originally thought to be peaceful and static, is actually very active-expanding during the day and contracting at night. Due to the influence of solar activity, the upper atmosphere has led to changes in the weather and climate of the earth.

In addition to affecting the weather on the earth, solar activity will also cause strange visual phenomena in the atmosphere. When electrons from the solar wind are captured by the geomagnetic field, they combine with air molecules in the atmosphere at the two poles of the earth. These air molecules will immediately glow, resulting in aurora.

Mars: Mars is the fourth planet in the solar system. Because the rocks, sand and sky on Mars are red or pink, this planet is usually called "red planet".

Mars has many characteristics similar to that of the earth. It has the same changes as the earth all year round; Its rotation period is more than half an hour longer than that of the Earth, and that of period of revolution is twice as long as that of the Earth, about 687 days. Mars is about half the diameter of the earth. The atmosphere of Mars is thinner than that of the Earth, of which 95% is carbon dioxide, 3% is nitrogen, and there is a very small amount of oxygen and water.

The dry surface of Mars is full of red soil and rocks. Martian soil contains a lot of iron oxide. Due to long-term exposure to ultraviolet rays, iron will form a layer of red and yellow oxides.

There have been floods on Mars and some small rivers on the ground, which clearly proves that many places have been eroded. So there is water on the surface of Mars, and there may even be great lakes and oceans.

Jupiter: Jupiter is the largest of the nine planets in the solar system, ranking fifth in the order from near to far from the sun. In ancient China, it was recognized that Jupiter runs once a week about 12 years, and Sunday is divided into twelve parts, which are called twelve times. Jupiter passes once a year, and the year can be determined by Jupiter's asterisk, so Jupiter is called the age star. It is the third brightest star in the sky, reaching -2.4 at its brightest, and only Venus and Mars are brighter than it. Jupiter has many moons. By the end of 1990, 16 satellites had been discovered. 1979, the interplanetary probe Voyager 1 also found that Jupiter has a very dark ring. Jupiter orbits the sun in an elliptical orbit with a half-length diameter of 5.205 astronomical units and an eccentricity of 0.048. It is about 0.5 astronomical unit closer to the sun at perihelion than at apohelion. The angle between Jupiter's orbital plane and the ecliptic plane is very small, only 1.3. Jupiter's period of revolution around the sun is 4332.589 days, about 1 1.86 years, and its average orbital speed is13.06 km/s. Jupiter is the fastest rotating planet in the solar system. The rotation period on the equator is only 9 hours, 50 minutes and 30 seconds, and the polar rotation is slightly slower. Due to high-speed rotation, its flatness is quite large, reaching 0.0648. Jupiter's axis of rotation is almost perpendicular to the road, and the angle between them reaches 86 55'. Jupiter's equatorial radius is 7 1400 km, which is 1 1.2 times that of the earth and its volume is 13 16 times that of the earth. The mass is 1.9× 1030g, which is more than 300 times larger than the mass of the earth and 2.5 times the total mass of the other eight planets. The average density is only 1.33g/cm3, the acceleration of gravity at the equator is 27.07m/s2, and that at the polar regions is 23.22m/s2. Jupiter has a dense atmosphere, mainly composed of hydrogen and helium, but also contains a small amount of ammonia, methane and water. Observing Jupiter with a telescope, we can see that there are a series of bright and dark clouds parallel to the equator in the atmosphere, and the shapes of the clouds change with time. This shows that there is violent motion in Jupiter's atmosphere. The surface temperature of Jupiter is very low. According to theoretical calculation, the effective surface temperature should be 105K, but the results measured by ground observation and interplanetary detector are higher than the theoretical value. The infrared observation of Jupiter also shows that the heat energy radiated by Jupiter is twice that received by the sun, which indicates that there is a heat source inside Jupiter. Jupiter also has a larger and stronger magnetosphere and radiation belt than Earth. The magnetosphere of Jupiter is 100 times larger than that of the earth. It can be divided into three areas. There is a strong radiation belt similar to the earth's radiation belt in the inner region (within 20 Jupiter radius from Jupiter's surface); The magnetic field lines in the middle region (from 20 Jupiter radius to 100 Jupiter radius) are distorted by centrifugal force. Both the inner region and the middle region rotate with a rotation period of about 10 hour. The magnetic field in the peripheral region (within the radius of 60-90 of Jupiter) is very weak and tends to zero at the boundary of magnetosphere. Except for the part very close to Jupiter's surface, Jupiter's magnetic field is dipole field, but the direction of the field is opposite to the geomagnetic field, that is, the compass pointing north on the earth becomes Jupiter's guide. The angle between Jupiter's magnetic axis and its rotation axis is 10.8. The magnetic field within the radius of Jupiter 3 is 4 or 8 poles, and the field strength is 3- 1 1× 10-4 Tesla. The Great Red Spot on Jupiter's surface is located on the south side of the equator, with a length of more than 20,000 kilometers and a width of about 1. 1 0,000 kilometers, which is slightly egg-shaped. It is found that in 1660, although its color and brightness have been changing for more than 300 years, its shape and size have hardly changed. The great red spot rotates counterclockwise around the center, and there is drift movement in the longitudinal direction, which is definitely not the surface feature of the solid. Now it is thought that it is likely to be a large vortex or a violent rising airflow. The vortex or airflow contains red phosphorus compounds, which may be the reason for the color of the great red spot. As for the reason why the Great Red Spot can exist for a long time, it is still unclear.

Saturn: Saturn is the second largest planet in the solar system. This is a beautiful planet. The most beautiful belongs to its aura. The diameter of the halo is very wide and bright. If you have a telescope more than 20 times at hand, you can sometimes see it at night. Saturn's rings can actually be divided into several different parts. The brightest and widest rings are ring A and ring B, and the darker ring is ring C. There are obvious cracks between the parts of the halo.

Pioneer 1 1 first visited Saturn in 1979, and travelers 1 and 2 also visited it in the same year. Now the Cassini spacecraft is on its way and is expected to reach Saturn in 2004. It will be responsible for exploring Saturn and its moon Europa.

Saturn's atmosphere is mainly composed of hydrogen, with a small amount of hydrogen and methane. Saturn is the loosest planet, and its density is even smaller than water.

Saturn's moons can't be ignored here. Quite a few. There are 18 named satellites, and some small satellites will be discovered soon.

Uranus: Uranus (a woody planet) with a maximum brightness of 5.6. When it is close to the zenith, people with good eyesight can hardly see it with the naked eye. The west calls it a god in Greek mythology. Uranus has an equatorial radius of about 25,400 kilometers, and its volume is 65 times that of the Earth, ranking third only after Jupiter and Saturn. Its mass is 14.6 times that of the earth, smaller than Jupiter, Saturn and Neptune, ranking fourth. 1977 found that Uranus also has a halo.

Uranus rotates once 15.5 hours. The density is only 1. 1.9g/cm3, and the acceleration of surface gravity is slightly greater than that of the earth. Objects can only leave Uranus at a speed of 21.22km/s. Because of the fast escape speed, it is difficult for gas to escape at such a high speed. Therefore, Uranus can bind a large amount of atmosphere and make it have a thick atmosphere on its surface. It is known from ground exploration and space exploration that the main components of Uranus surface atmosphere are hydrogen and helium. Most of them are hydrogen, and the content of helium is 10% ~ 15%. In addition, there are a small amount of other gases.

In the planetary world, Uranus has a unique feature, that is, its equatorial plane and orbital plane are inclined at 97 degrees and 55 minutes. In other words, the angle between Uranus' axis of rotation and its orbital plane is very small, and it is almost lying in its orbit. As you can imagine, moving in this posture will complicate the four seasons and day and night phenomena on Uranus. First of all, the north and south poles of Uranus are basically on its orbital plane, and the equatorial plane is basically perpendicular to the orbital plane. When its south pole is facing the sun, and it is summer in the southern hemisphere, the south pole is almost exposed to direct sunlight, and the horizon height of the sun seen by the southern hemisphere decreases with the decrease of latitude. Moreover, during the rotation of Uranus, the sun seen in the southern hemisphere did not set at this time, that is, the southern hemisphere was basically daytime. On the contrary, it is winter in the northern hemisphere at this time, and the sun will never rise above the horizon and live a long night. Uranus' orbit around the sun is big and slow. The half-length diameter of its orbit around the sun is about 19.27 astronomical units, and the orbital eccentricity is about 0.046. The period of motion around the sun is about 84 earth years. It can be seen that for the poles of Uranus, it is basically equivalent to 42 years of day and 42 years of night on the earth.

Neptune: Neptune is the eighth planet from the sun. It was discovered on September 23rd 1846 through its perturbation effect on the orbit of Uranus. The calculator is French astronomer Le Ye Wei. German astronomer J.G. Galle was the first person to observe the planet according to the calculated position. This discovery is regarded as an example of the accuracy of the theory of planetary motion.

Because Neptune is far away and its luminosity is dim, it is difficult to see its surface details even with a large telescope, so it is impossible to determine its rotation period by observing the movement of surface markers. 1928, by observing the Doppler shift of spectral lines, the rotation period is 15.8+- 1 hour. The current rotation period was determined by Bertone et al. by analyzing about 300 infrared observations.

Neptune's rapid rotation makes its oblateness reach 1/50 (that is, the equatorial radius is about 500 kilometers longer than the polar radius). 1April 7, 968, Neptune occulted the stars. Through the observation of this event, it is concluded that the equatorial diameter is 50950 kilometers, which is quite different from the latest data.

Neptune looks slightly green with a telescope. 1932 proves that the strong absorption line in the infrared region of Neptune's spectrum is caused by methane. Its atmosphere is rich in hydrogen and helium, and its atmospheric temperature is about -205 degrees Celsius, which is higher than the expected value calculated according to solar radiation, indicating that either Neptune has a greenhouse effect in the lower atmosphere or it has an internal heat source.

1846, W. Russell discovered the retrograde triton. According to calculations, it is approaching Neptune and may break into Neptune's ring in the future. 1949, triton was discovered.

Neptune is one of the nine planets in the solar system, with an average temperature of-193 degrees Celsius to-153 degrees Celsius and an atmospheric pressure of about 1-3 Pa. Ranked eighth according to the average distance from the sun, with an orbital radius of 4.5 billion kilometers, period of revolution 165. Neptune brightness 7.85, etc. You can only see it through a telescope. Its diameter is 49,400 kilometers, which is 3.88 times that of the earth. Its equatorial radius is about 64 1 km longer than the polar radius.

Neptune's volume is about 57 times that of the Earth, its mass is 17.22 times that of the Earth, and its average density is 1.66 g/cm3. The acceleration of gravity on the surface is slightly greater than that of the earth, with two poles 1, 180 cm/s and equator about 1, 100 cm/s. The escape velocity of surface objects is 23.6 km/s.

Neptune has six moons and five rings. Because Neptune is a light blue planet, people call it Neptune according to the traditional naming method of the planet. Neptune is the sea god who rules the ocean in Roman mythology. He holds the universe of 1/3, which is quite amazing.

Pluto: Pluto is the planet with the farthest average distance from the sun and the smallest mass among the nine planets in the solar system. Pluto hobbles in the cold and dark space 5.9 billion kilometers away from the sun, which is very similar to proto, the god of the underworld in Roman mythology. Therefore, people call him Pluto. Pluto has a satellite called Chalong. Pluto is about 2400 kilometers in diameter, which is smaller than the moon, while Chalong is 1, 180 kilometers in diameter, and the ratio with Pluto is 2: 1, which is the largest ratio of planets to satellites among the nine planets. Pluto is 0.0024 times the mass of the earth, not only smaller than Mercury, but even smaller than the moon. Its density is per cubic centimeter 1.8-2. 1g and its albedo is 50%-60%. Pluto was discovered by Tombaugh at193065438+1October 2 1, and Lovel made an indelible contribution to the discovery of Pluto.

1978 discovered that Pluto has a satellite (Ka Rong). The surface of this satellite seems to be different from Pluto, and it seems to be covered with more ice than solid methane. Because its orbit is fixed by Pluto's gravity, the two are always opposite in the same hemisphere.

Pluto is still a mysterious planet because no spacecraft has visited it. Because Pluto is so far away from the sun, its surface temperature is almost close to MINUS 240 degrees Celsius. On Pluto, the sun looks like a bright star.

Ground observation shows that the surface of Pluto is covered with solid methane, and its atmosphere is very thin. As Pluto moves away from the sun, this thin layer of gas will gradually solidify on the surface. NASA plans to send a spaceship to Pluto in 20001year, which will enable scientists to study the distant planet before its atmosphere freezes.

There may be the 10 planet, but it has not been discovered yet, waiting for our human exploration.