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 as a dwarf planet), 66 satellites (originally 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, which are close to the sun, are called terrestrial planets. Spacecraft have detected them all and landed on Mars and Venus, and achieved important results. Their common feature is high density (>: 3. g/cm3), small volume, slow rotation, few satellites, mainly silicate inside, with a solid shell. Jupiter, Saturn, Uranus and Neptune, which are far away from the sun, are called jovian planets. They all have thick atmospheres, and their surface features are difficult to understand. Generally speaking, they all have solid cores similar to terrestrial planets. There are more than 1, asteroid (that is, irregular small stars composed of rocks) between Mars and Jupiter. It is speculated that they may be formed by the fragmentation of a planet located between Mars and Jupiter, or some rocky fragments that 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 except Mercury's, they are very close to a circle. Planetary orbits are more or less in the same plane (called ecliptic plane and based on the orbit plane of the earth). The ecliptic plane is only 7 degrees inclined to the equator of the sun. Pluto's orbit is mostly out of the ecliptic, with an inclination of 17 degrees. The chart above shows the relative size and relationship of each orbit from a specific perspective angle higher than the ecliptic plane (the phenomenon of non-circle is obvious). They orbit in the same direction (counterclockwise from the north pole of the sun), so scientists exclude Pluto from the nine planets. Besides Venus and Uranus, the direction of rotation is also the same.
the position of the solar system in the universe
the solar system is located at the edge of the milky way galaxy
the solar system is a celestial system composed of the sun and celestial bodies orbiting it 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. This diagram shows the relative sizes of the planets and the sun.
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 accounts for 99.85% of the total mass of the whole solar system. The rest of the mass includes planets and their satellites, planetary rings, and interplanetary substances such as asteroids, comets, Kuiper Belt objects, outer Neptune objects, theoretical Oort clouds, dust, gas and particles between planets. The total surface area of all celestial bodies in the whole solar system is about 1.7 billion square kilometers. The sun tightly controls all the celestial bodies in the solar system around itself with its strong gravity, making them rotate around itself in an orderly manner. At the same time, the sun moves around the center of the Milky Way with all the members of the solar system.
so far, eight large 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 with different sizes and shapes between Mars and Jupiter. Astronomers call this area the asteroid belt. In addition, there are more than 1 comets in the solar system, and countless small celestial bodies such as dust, ice balls and fragments.
The 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 terrestrial 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.
Origin and evolution of the solar system
See also the origin and formation age of the solar system
It is generally thought that the planetary system is a part of the process of star formation, but some scholars think that it was almost formed by the collision of two stars. The most common theory is that the solar system was formed from 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 center of gravity energy becomes radiated infrared, and the rest increases the temperature of the core. The core begins to take the shape of a disk.
2. When the density and temperature track are high enough, deuterium fusion combustion begins to occur, and the outward pressure of radiation slows down (but does not stop), which is close to the collapse of other cores.
3. Other raw materials continue to fall to this protostar, and their angular momentum may lead to bipolar flow.
4. finally, hydrogen begins to melt in the core of the star, and the remaining surrounding materials outside are removed.
The hypothesis of solar nebula was put forward by Immanuel Kant in 1755. He said that the solar nebula rotates slowly, and gradually condenses and smoothes due to gravity, eventually forming stars and planets. A similar model was proposed by Laplace in 1796.
the diameter of the solar nebula is about 1AU 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 accumulate into blocks, which will become the future planets. The outside of the nebula is getting colder and colder, so the inner planet has a lot of heavy minerals, while the outer planet is gas or ice. Taiyang Yuan was formed about 4.6 billion years ago, and various planets formed in the next 8 million years.
the movement of the solar system
the solar system is a part of the milky way galaxy. The Milky Way is a spiral galaxy with a diameter of 1, light years, including more than 2 billion stars. The sun is a typical star in the Milky Way, about 25, to 28, light years away from the center of the galaxy. The solar system moves at a speed of about 22 kilometers per second, and rotates once in the galaxy for 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 in the same direction around the sun, mostly in elliptical orbits, and generally the period of revolution is longer.
exploration and study of the solar system
out of the desire to know about the living environment and the increasingly tight earth resources, human beings have been exploring the solar system through space detectors since 1959. At present, it mainly focuses on the exploration of the moon and Mars and the detection of asteroids and comets.
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 sources, element and isotope abundances), physical-chemical properties, chronology and chemical evolution of solar system celestial bodies. Chemistry of the solar system is closely related to the origin of the solar system.
* solar system physics: A subject that studies the physical characteristics, chemical composition and cosmic environment of planets, satellites, asteroids, comets, meteors and interplanetary substances in the solar system.
* gravitational law in the solar system: the law followed by gravitational interaction among celestial bodies in the solar system.
* Stability of the solar system: one of the basic problems in astroevolution and astromechanics
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. Dozens of planetary systems have been discovered so far, but there are still few detailed materials. The discovery of these planetary systems depends on the Doppler effect. By observing the periodic changes of the star spectrum, we can analyze the changes of the speed of the stars, infer whether there are planets, and calculate the mass and orbit of the planets. Using this technology, only large planets with wood stars can be found, but planets the size of the earth can't be found.
In addition, another purpose of studying celestial bodies 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 following table are all relative to the Earth: (The number of satellites is as of the end of 25)
The data comparison table between the sun and the eight planets (the equatorial diameter is 637km), 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 discovered satellites
Sun 19 333, 4-27.275-
Mercury .39 .382 .5528 .3871 7.5 .24852 58.6
Venus .72.949 .82.723.4.615 243.185 (reverse rotation) . 1. 1. .9973 1
Mars 1.5.53 .11 1.52 1.88 1.26 2
Jupiter 5.2 11.2 318 5.2 1.3 11.86 .4135 63
Saturn 9.5 9.41 95 9.54 2.5 29.46.11 7 (there are 34 named ones)
Uranus 19.23.98 14.6 19.22 .8 84.1 .7183 29
Neptune 3.13.81 17.2 3.6 1.8 164.79 .6713 13
* In 193, Pluto was officially recognized as a planet by the International Astronomical Union, but some of them.
* According to the resolution of the General Assembly of the International Astronomical Union on August 24, 26, Pluto is regarded as a "dwarf planet" in the solar system and is no longer regarded as a planet.
The tenth largest planet in the solar system
At the end of the 19th century, many astronomers speculated that there were other planets besides Neptune, because the orbit of Neptune was different from that calculated by theory. They call this star "Planet X", which means unknown planet.
American astronomer Percival Lowell searched for planets other than Neptune twice in 199 and 1913, but failed to find them. After 1915, Lowell published a paper and wrote the estimated planetary data. In fact, in that year, his observatory took photos of Pluto, but it was not until 193 that he recognized it as a planet.
But Pluto's mass is too small to explain Neptune's orbit. Astronomers continue to search for "planet X", but the name has the meaning of the tenth largest planet, because X is Latin for 1. It was not until Voyager 2 approached Neptune that it was discovered that the mass of Neptune had been miscalculated a lot. With the correct mass and the influence of Pluto, Neptune's actual orbit is consistent with its calculated orbit.
according to the planetary orbit, a planet about the size of the earth can't be within 6AU (Pluto is now about 3AU from the sun). If there is indeed the tenth planet, its orbit will be very inclined, and it is likely that the celestial bodies in other galaxies are too close to the sun and are attracted into orbit by the sun.
The status of Pluto has always been controversial in the astronomical community. 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 24th, 26, Pluto is regarded as a "dwarf planet" in the solar system, and is no longer regarded as a planet.
Since the 21st century, scientists have discovered three larger planets in the outer periphery of Pluto. The sequence is "Sedna" discovered in 24, with the code name of 23VB12; In 25, the "Santa", code-named 23 EL61 and code-named 23 UB313 (whose names were not announced by the discoverer) was published at the same time.
on July 19th, 25, American scientists discovered 23 UB313. Researchers estimated that it was 3, kilometers in diameter, and some people thought it was probably the tenth largest planet in the solar system. The discoverer had applied to the International Astronomical Association for approval.
"planet in water"
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 "Vulcan Star" after a Vulcan, but astronomers have not found this planet after more than 5 years of observation.
The hypothesis of "planets in water" has been ruled out by Einstein's general theory of relativity. The gravitational theory of general relativity explains the strange motion of Mercury, but astronomers have not given up their search for "planets in water".
Other information
There are many celestial bodies in the solar system that contain solid surfaces and have a diameter of more than 1 km, with a total surface area of 1.7 billion square kilometers.
some people think that the sun is actually the main star of a binary system, and there is a companion star named "Misis" in a distant place. This hypothesis is used to explain the regularity of mass extinction on the earth. It is believed that its companion stars will disturb asteroids and comets in the system, make them change their orbits and rush into the solar system, increase the chance of hitting the earth and cause periodic mass extinction.
Planetary planets
Earth-like planets are formed by colliding and gathering solid particles into tiny planets, and then gathering tiny planets.
Woodlike planets start from the mutual adsorption of water and ice, and then further adsorption occurs after the mass is large enough.