The solar system is located at a distance ofGalaxyThe center is approximately estimated at 24000~27000 light years(The number of stars in the Milky Way is between 100 billion and 400 billion, and the sun is just one of them).The sun goes around at 220 km/sSilver coreThe movement, about 250 million years around, the earth's climate and the overall nature also occurred 250 million yearsPeriodic change。The direction of the sun's movement is basically towardlyra , nearHerculesDirection of.
As of October 2019, the solar system includessunlight, 8planet, nearly 500satelliteAnd at least 1.2 millionasteroid。Some moredwarf planetandcomet。IfNeptuneAs the boundary of the solar system, the diameter of the solar system is 60Astronomical unitAbout 9 billion kilometers.If the heliosphere is taken as the boundary, the sun can reach 100 astronomical units (the thinnest place) from the solar system boundary.IfOort CloudThe diameter of the solar system may be 200000 astronomical units.
The formation of the solar system began with the gravitational collapse of a giant interstellar molecular cloud about 4.6 billion years ago.Most of the mass in the solar system is concentrated in the sun. Among the remaining celestial bodies, Jupiter has the largest mass.planetsanti-clockwiseIt revolves around the sun.In addition, there are smaller objects between Jupiter and MarsAsteroid belt。Kuiper beltandOort CloudThere are also a large number of small objects.There are many moons circling around planets or small bodies.Every planet outside the asteroid belt hasPlanetary ring。
In 2023,Scientists from the French National Center for Scientific Research and other institutions have discovered the aurora mechanism that may be prevalent in the solar system.[54]
In ancient times, people noticed that the relative positions of many stars in the sky were constant.But five bright stars are constantly moving among the stars.Therefore, "moving" stars are called "planets", and "immovable" stars are called "stars".The ancient Chinese named the planets respectively, namely:Mercury、Venus、Mars、JupiterandSaturn。Mercury, also called Chenxing, is the closestsunlight, no more than one day (30 degrees).Venus is also called Taibai orVenus, Changgengxing.It is the brightest star in the sky;Mars is also called "Mars" because of its fiery red color;Jupiter, also known as Jupiter, has been in orbit for about 12 yearsOne day a week, almost once a year (the whole day is divided into twelve times), which was used to count the years in ancient times;Saturn is also called Zhenxing or fill star, because it runs for about 28 years, and guards for one night a year (in ancient China, the whole sky was divided intoTwenty eight nights）。These are the five planets that can be seen by the naked eye. In ancient China, they were collectively called "Five Stars", and the sun and moon were collectively called“Qiyao”。ancient GreekPeople call the five brightest celestial bodies (Mercury, Venus, Mars, Jupiter and Saturn) in the skyplanet, means rover, which is the origin of the word "planet".
Kant, German philosopher.
But for a long period of time in history, human beings did not know or understand the concept of the solar system.untilThe RenaissanceAt that time, most people still believe that the earth is still motionless, and the earth is at the center of the universe.Philosopher of ancient GreeceAlistairOnce speculated thatHeliocentric theorySystem, but untilCopernicusOnly then did he put forward the first heliocentric theory of the universemathematical model 。In 1755, German philosopherKant First of allOrigin of the solar systemOfNebula hypothesis。41 years later, the famous French mathematician and astronomerLaplaceThe nebula hypothesis on the origin of the solar system has also been independently proposed.[5]Following the nebula theory“Cataclysm theory”、“Capture theory”And so on.
In the 15th century,CopernicusLike previous Indian mathematicians and astronomersAyeportAnd the Greek philosopher Aristarchus, who rearranged the structure of the universe with the sun as the center, which was still the most forward-looking concept at that time.
seventeenth century, viaGalileo、KeplerandNewtonUnder the leadership of, people gradually accept the fact that the earth will not only move, but also revolve around the sun;At this time, new understanding also emerged, such as the planets are dominated byLaws of physicsIt is dominated by the same substances and phenomena as the earth:crater, weather, geology, season and polar cap.
The first telescope in human history was made by Galileo in 1609.
GalileoIt's the first discoverycelestial bodies Astronomers of detail.He found craters on the moon, sunspots on the surface of the sun, and four satellites around Jupiter.HuygensFollowing Galileo's discovery, he discovered Saturn's moons Titan andSaturn RingThe shape of.SuccessorCassiniFound four moons of Saturn, and the rings of SaturnCassini division JupiterGreat erythema。
In 1705,edmond halley ObservedHalley's Comet。This is the first evidence that the sky will revolve around the sun except for the planets.
In 1781,William Herschel The discovery of Uranus, the first planet to be discovered.
In 1801,Giuseppe Piazzi findCeresThis is an asteroid between the orbits of Mars and Jupiter. At first, it was regarded as a planet.However, it was later found that there were as many as tens of thousands of small objects in this area, which led to their classification as asteroids.
In 1846, the orbit error of Uranus led many people to doubt whether there was anotherMegaplanetsExert force on him at a distance.Le VieThe result of the calculation was the discovery of Neptune.In 1859, scientists found that there were someNewtonian mechanicsInexplicable minor motion (Mercury perihelion precession).But this movement has finally proved that it can be usedGeneral relativityTo explain.
To explain the apparent deviation of Neptune's orbit,Percival Lowell It is believed that there must be a planet outside.After his death, hisLowell observatoryThe search continued, and finally in 1930ThompsonPluto was discovered.However, Pluto is so small that it is not enough to affect the orbit of the planet, so its discovery is purely coincidental.
In 2005, Migao Brown, Chad Trujillo andDavid Rabinowitz Announce discoveryEris It is the largest object on the discrete disk larger than Pluto, and it is the largest object circling the sun after Neptune.
On August 24, 2006, the 26th International Astronomical UnionBraggHeld.The meeting redefined the term planet, and for the first time excluded Pluto from the list of major planets and classified it as a dwarf planet.Five dwarf planets have been identified:Ceres（Ceres）、Pluto（Pluto）、Eris （Eris）、Bird God Star（Makemake）、Haumea （Haumea）。
Space exploration
Color panoramic photos of Mars taken by Viking 1.[6]
All planets in the solar system have been launched by humansspacecraftVisited and conducted research to varying degrees.In the case of a lander, some experiments on soil and atmosphere were also carried out.
Mercury was photographed from the Mariner 10 spacecraft on March 29, 1974.[6]
In 1959, the United States launched Pioneer 6, the first to send images back from spaceArtificial satellite。
In 1962,Mariner 2 It successfully orbited Venus and became the first man-made object to orbit other planets.
On July 14, 1965, NASAMariner 4 It became the first spacecraft to fly over Mars, and also the first spacecraft to send back black and white images of the surface of Mars.[6]
In 1973,Pioneer 10 Fly over Jupiter and become the first ship to explore Jupiter like planetsspacecraft。
Neptune's big black spot observed by Voyager 2 spacecraft in 1989.[6]
On March 29, 1974,Mariner 10 It became the first man-made object successfully orbiting Mercury.In the three flyovers, Mariner 10 photographed Mercury's nearly half of the planet's surface, which is very similar to the moon.The 1991 radar observation showed that Mercury's polar regions might be covered with ice.[6]
Mercury's Karolis Basin was photographed by Messenger on February 25, 2015.[6]
In 1979,Pioneer 11 Become the first spacecraft to visit Saturn.In the same year, NASA'sVoyager 1The spacecraft discovered Jupiter's giant rings.From 1979 to 2007, includingVoyager 2andUlyssesEight NASA probes were sent to Jupiter to study its atmosphere, satellites and rings.
On January 24, 1986, NASA's Voyager 2 flew over Uranus for the only time. It found 11 new satellites, two new star rings and a stronger magnetic field than Saturn.[6]
In 1989, NASA's Voyager 2 became the first and only spacecraft ever to visit Neptune.[6]
On August 3, 2004, NASA launched the Mercury probe——Messenger。After three flyovers, MESSENGER entered the orbit of Mercury on March 17, 2011, and began to study the composition, core structure, magnetic field and polar materials of Mercury.[6]
On September 13, 2014, NASA held a press conference to announce that the“Voyager One”The probe has left the solar system and is flying to other stars."Voyager 1" is also the first aircraft made by humans that rushed out of the solar system, and it has become a milestone of great commemoration in the history of human aerospace.[52]
In 2023,Scientists from French National Scientific Research Center and other institutions, usingData of Mercury probe "Beppy Columbus" flying over Mercury for the first time, and discovered the auroral mechanism that may exist universally in the solar system.[54]
Manned detection
The Mir space station and the Blizzard space shuttle of the former Soviet Union.
On April 12, 1961,Yuri Gagarin takeDongfang No.1blast off.The first person to walk on a celestial body outside the earthNeil Armstrong He completed the Apollo 11 mission on the moon on July 21 in 1969.First in orbitspace stationIt's NASA“Space laboratory”。The first space station that can really let people live in space is the Mir space station of the former Soviet Union. It has been in orbit for nearly ten years from 1989 to 1999, and was retired in 2001.SuccessorThe International Space StationSince then, it has continued to sustain human life in space.On October 15, 2003, ChinaShenzhou VManned spacecraftstayJiuquan Satellite Launch CenterThe launch was China's first manned space flight.On October 17, 2016, China launched a manned spacecraft at Jiuquan Satellite Launch CenterShenzhou 11, and withTiangong No.2automaticRendezvous and dockingsuccess.
Human exploration of the solar system has never stopped. In the future, more probes and astronauts will visit the celestial bodies in the solar system.
There are many theories about the formation of the solar system, one of which isNebula hypothesisFrom 1755Kant And 1796LaplaceThey are proposed independently.Kant believed that the solar system was composed of a hugeMolecular cloudIs formed in collapse.The nebula was originally light years in size, and several stars were born at the same time.The elements traced back from ancient meteorites show that only the core part after the supernova explosion can produce these elements, so the star cluster containing the sun must besupernova remnant Near.Probably fromSupernova explosionOfseismic wavesThe density of the nebula near the sun increases, so that gravity can overcome the expansion pressure of the internal gas and cause collapse, thus triggering the birth of the sun.[2]With modern timesAstrophysicsAnd the development of physics, especially the establishment of the theory of stellar evolutionModern nebula theory, and gradually occupiedleading role 。According to the observational data and theoretical calculations, the modern nebula hypothesis puts forward its main point: the primitive nebula of the solar system is hugeInterstellar cloudA disintegrated molecular cloud rotates at the beginning and shrinks under its own gravity. The central part forms the sun, the outer part evolves into a nebula disk, and the nebula disk later forms planets.[7-8]
The art of the formation of the solar system.
When this region will form before the solar system, it is called preSolar nebula, collapse becauseConservation of angular momentumAnd make it rotate faster and faster.[9]The center concentrates most of the mass and becomes a hotter area than the surrounding disk.The shrinking nebula turns faster and faster, and it begins to flatten intoProtoplanetDisk, about 200 AU in diameter, with high temperature and density in the centerProtostar。Planets are formed by accretion in the disk, and gradually condense to form larger and larger objects under the mutual attraction of dust and gas。There may be hundreds of protoplanets in the early solar system, but most of them were merged or destroyed, leaving behind planetsdwarf planetA small body composed of remains.silicateAnd metals have very high melting points, and only they can maintain solid form at the temperature of the inner solar system. These materials eventually form rocky planets, which areMercury、Venus、earthandMars。Because the metal composition only occupies a small part of the original solar nebula,terrestrial planetThey haven't developed very much.Freezing line between Mars andJupiterPosition between,Giant planet(JupiterSaturn、UranusandNeptune）It is formed on the outside of the freezing line, where the temperature is very low, and volatile matter can exist in solid form.There is more ice in this area than metals and silicates that make up Earth like planets, so the planets in this area are very developed and can capture a lot of hydrogen and helium, which are the most abundant elements in the solar system.The rest of the solar system, which is impossible to form planets, gathers inAsteroid belt、Kuiper beltandOort CloudArea.[10]
In the first 50 million years, at the center of the protostar, the density and pressure of hydrogen are large enough to occurThermonuclear reaction。stayReaction processMedium, hydrogen temperaturereaction rateThe pressure and density are increasing until the thermal pressure of the fluid counteracts the gravity and reaches a static equilibrium state.So far, the sun has become aMain sequence star。The main sequence star stage of the sun lasts about 10 billion years from the beginning to the end, while all other stages, including the life span of debris, only have a total of 2 billion years.Solarsolar windFormedHeliosphereAnd blow the residual gas and dust from the protoplanetary diskInterstellar space, hindering the development of planets.Since then, the sun has become brighter, and the brightness of the main sequence star in the early days is only 70% of today's brightness.[11]
Solar system range
According to astronomers, the solar system will last until the sun leavesMain preface。Since the sun uses its internal hydrogen as fuel, in order to use the remaining fuel, the sun will become hotter and hotter, so the burning speed will be faster and faster.This causes the sun to keep brightening at a rate of about 10% every 1.1 billion years.In about 1.6 billion years, the core of the sun will be hot enough to fuse the outer hydrogen, which will cause the sun to expand to 260 times the radius, becoming aRed Giant。At this time, due to the volume andSurface areaThe total luminosity of the sun increases, but the surface temperature decreases, and the luminosity per unit area darkens.Then, the outer layer of the sun is gradually thrown away, and finally the core is exposed as aWhite dwarfOnly the size of the earth has half the mass of the original sun.In the past ten trillion years or so, it will be possible to formBlack dwarf。[12-13]
There are still different schools of thought in the modern nebula theory, and there are still many differences between these schools, which need further research and confirmation.[7]
Schematic diagram of the structure of the solar system.
The most important member of the solar system is the sun, which is a G2Main sequence star, accounting for all known masses in the solar systemninety-nine point eight six%, the celestial bodies in the solar system move under the constraint of solar gravity.Of the remaining mass, 99% is composed of the four major objects in the solar system, namely giant planets, and Jupiter and Saturn together account for more than 90% of them.Other celestial bodies in the solar system (including 4 Earth like planets, dwarf planets, satellitesasteroidandcomet）The total mass is less than 0.002% of the solar system.
The big bodies that circle the sun lie on the earthTrack plane——Ecliptic——Nearby plane.The planets are very close to the ecliptic, andKuiper beltCelestial bodies usually have obvious tilt angles.All planets and most other celestial bodies in the solar system revolve around the sun in the same direction (from Earth'sarcticAerial view is counterclockwise), but there are also reverse directions, such asHalley's Comet。
sunlightThe detected areas in the system are generally divided into the sun, four smaller planets in the asteroid belt and four in the Kuiper belt outside the asteroid beltGiant planet。Astronomers sometimes informally divide these structures into different regions.Inner solar systemIt includes four terrestrial planets and asteroid belt.Outer solar systemOutside the asteroid belt, there are four giant planets.Beyond the Kuiper Belt is the Oort Cloud, which is a known boundary region of the solar system.
solar systemplanetsAccording to its physical properties, it can be divided into two groups:terrestrial planet：Small and average sizedensityLarge,rotationSlow speed, few satellites, including Mercury, Venus, Earth and Mars;The other isJupiter like planet：Large size, small average density, fast rotation speed, more satellites, there are Jupiter, Saturn, Uranus and Neptune, and the most special ones are Neptune and Saturn.
There is another kind of celestial body in the solar system, which surroundsSolar motionIts own gravity is enough to overcome its solid stress to make itself round and spherical, but it cannot clear other objects near its orbit. It is called a dwarf planet.yesPluto、Ceres、Eris 、Bird God Star, andHaumea (as of 2009).
The third type of objects in the solar system are small objects in the solar system, including comets and asteroids. They are the most numerous objects in the solar system, with the total number of asteroids at least 1.2 million.[1]
Picture of the motion of the solar system in interstellar space.
The sun is constantly emittingElectron flow（plasma）, also known as the solar wind.This oneMicroparticleThe flow speed is 1.5 million kilometers per hour, creating a thinatmosphere（Heliosphere）, with a range of at least 100 AU（Heliospheric zenith）This is OKInterstellar matter。The sunspot cycle of the sun (11 years) and frequent flaresCoronal mass ejectionThe interference caused in the solar circle produces the space climate.The magnetic field rotating with the sun's rotation is generated in the interplanetary matterHeliospheric current sheetIs the largest structure in the solar system.
The earth's magnetic field protects from the interaction with the solar windEarth's atmosphere。Mercury and Venus have no magnetic field, and the solar wind gradually drains their atmosphere into space.Solar wind andGeomagnetic fieldThe aurora generated by the interaction can be seen near the magnetic poles close to the earth (such as the South Pole and the North Pole).
cosmic rayIt comes from outside the solar system. The solar circle shields the solar system. The magnetic field of the planets also provides some protection for the planets themselves.Cosmic rayInterstellar matterDensity andSolar magnetic fieldThe intensity of the cycle changes.Therefore, it is still unknown how much cosmic rays vary in the solar system.
The interplanetary matter is in at least two disk regionsCohesive setbecomeCosmic dust。The first region is the ecliptic dust cloud, located in the inner solar system, and isEcliptic lightThe cause of.They may be produced by the collision between the celestial bodies and planets in the asteroid belt.The second region extends about 10-40 astronomical units, which may be caused by the collision of objects in the Kuiper Belt.
scale
Comparison of the sizes of the eight planets and the sun.
The distance from the earth to the sun is defined asoneAstronomical unit（150000000 km）。For comparison, the radius of the sun is 0.0047AU（700,000 km）。The volume of the sun only accounts forEarth orbitThe radius is 0.00001% (10−5%), and the volume of the earth is only about one millionth of that of the sun (10−6）。Jupiter, the largest planet in the solar system, is 5.2 AU (780000000 km) away from the sun, with a radius of 71000 km (0.00047 AU), while Neptune, the farthest planet, is 30 AU (4.5 × 10 AU) away from the sunninekm）。
Distribution map of the Swedish solar system model.
The solar system model with the largest scale——Swedish solar system model——Use atStockholm110mSpherical gymnasiumAs a substitute for the sun.Could be a dwarf planetsedna It is a 10cm ball 912km away.If the distance between the sun and Neptune is 100 meters, then the sun is just a small ball with a diameter of about 3 centimeters, and the scale of all giant planets will be less than 3 millimeters, while the diameter of Earth and other terrestrial planets will be smaller than oneflea(0.3 mm) is much smaller.[16]This shows that the scale of the solar system is very large, the planets are far away from each other, and the volume difference is huge.
operating mechanism
The motion of planets and their satellites in the solar system has the following common characteristics:
① The orbital eccentricity of all planets is very small, almost all close to circular.
② Each planet's orbital plane is approximately located on a planeTrack surfaceorEcliptic surfaceThe inclination of is also small.
③ All the planets revolve around the sun from west to east.Except Venus and Uranus, the rotation direction of other planets is also from west to east, that is, the same as the revolution direction.
④ Except for Uranus, the equator of other planets inclines slightly towards the orbital plane.
⑤ The orbits of most satellites are nearly circular, and their orbital planes are close to the equatorial planes of their parent stars.
⑥ Most satellites, includingSaturn RingInside, the revolution direction is the same as that of the parent star.[17-19]
Main parameters of eight planets
planet
Track semimajor axis
（AU）
Revolution period
Average track speed
（km·s-1）
Eccentricity
Inclination to ecliptic plane
Angle of intersection between equator and orbital plane
Mercury
zero point three eight seven zero nine
87.9674 days
forty-seven point eight nine
zero point two zero five six
7.00°
zero
Venus
zero point seven two three three two
224.6960 days
thirty-five point zero three
zero point zero zero six eight
3.39°
177.3°
earth
one
365.2564 days
twenty-nine point seven nine
zero point zero zero one seven
——
23.45°
Mars
one point five two three six six
686.9649 days
twenty-four point one three
zero point zero nine three four
1.85°
25.19°
Jupiter
five point two zero three three six
11.862615
thirteen point zero six
zero point zero four eight three
1.31°
3.12°
Saturn
nine point five three seven zero seven
29.447498
nine point six four
zero point zero five four one five
2.48°
26.73°
Uranus
nineteen point one nine one two six
84.016846
six point eight one
zero point zero four seven one six
0.76°
97.86°
Neptune
thirty point zero six eight six nine
164.79132
five point four three
zero point zero zero eight five eight
1.77°
29.58°
planet
Equator radius: Earth
Mass: Earth
Average density
（g/cmthree）
Equatorial escape velocity
（km/s）
Rotation period
Number of satellites
Mercury
zero point three eight two five
zero point zero five five two seven
five point four three
four point two five
58.6462 days
zero
Venus
zero point nine four eight eight
zero point eight one five zero zero
five point two four
ten point three six
243.0187 days
zero
earth
one
one
five point five one
eleven point one eight
23.9345 hours
one
Mars
zero point five three two two six
zero point one zero seven four five
three point nine four
five point zero two
24.6230 hours
two
Jupiter
eleven point two zero nine
three hundred and seventeen point eight one six
one point three three
fifty-nine point five four
9.9250 hours
92+ring
Saturn
nine point four four nine
ninety-five point one six zero nine
zero point seven zero
thirty-five point four nine
10.6562 hours
145+ring[20]
Uranus
four point zero zero seven
fourteen point five three seven three
one point three zero
twenty-one point two nine
17.2399 hours
27+ring
Neptune
three point eight eight three
seventeen point one four seven one
one point seven six
twenty-three point seven one
16.1100 hours
13+ring
reference material:[21]
sunlight
The sun is located in the center of the solar system and is the nearest star to the earth.It is inGalaxydistanceSilver coreAbout 10 thousand second differenceHunter armOn.It is a hot glowing gas ball, and its internal high temperature and pressure maintainnuclear fusionSo as to provide huge energy.The surface temperature of the sun is as high as 6000K, and the central temperature is as high as 15 million Kelvin.The diameter of the sun is 1392000 kilometers, 109 times that of the earth.The volume of the sun is 14.1 billion cubic kilometers, 1.3 million times that of the earth.The mass of the sun is nearly 200 billion tons, 330000 times that of the earth. It concentrates 99.865% of the mass of the solar system.
Schematic diagram of the internal structure of the sun.
The corona of the total solar eclipse on March 7, 1970 - the corona of the solar maximum year.[22]
The sun, like the earth, hasatmosphere。The solar atmosphere can be divided intophotosphere、ChromosphereandCoronaThree floors.The photosphere layer is about 5000 kilometers thick, and the visible light is almost all emitted by the photosphere.The bright area on the photosphere is calledfacula, dark spots calledSunspotThe activity of sunspots has an average period of 11.2 years.The chromosphere layer is from the photosphere surface to the height of 2000 kilometers.The chromosphere layer hasProminenceandsolar flareActivities.Beyond the chromosphere is the corona, which is extremely hot.The corona must beTotal solar eclipseOccasionallyCoronagraphCan be observed.[22]
The Messenger spacecraft took a composite image of Mercury.
Mercury(Mercury) (☿), the planet closest to the sun in the solar system, with an average revolution speed of about 48 km/s, is the fastest planet in the solar system,Revolution periodAbout 88 days.MercuryRotation period58.646.Every time the earth rotates, it is a day and night, while Mercury rotates three times, it is a day and night.The time of one day and night on Mercury is equivalent to 176 days on Earth.At the same time, Mercury also revolved for two weeks.Therefore, one day on Mercury is equal to two years.Because Mercury always faces the sun at the same longitude at perihelion, and faces the sun at the longitude 90 ° apart at aphelion, Mercury changes seasonally with different longitude.Mercury's orbit around the sun is a relatively flat ellipse. When it is at perihelion and aphelion, the size of the sun seen can be more than twice that.In addition, there is neither air nor water on Mercury. The temperature difference between day and night is very different, reaching 427 ℃ at the hottest time and - 173 ℃ at the coldest time.The surface of Mercury is dotted with large and small ringed mountains, including high mountains, plains, and cliffs.According to statistics, there are thousands of craters on Mercury, and the slopes of these craters are more gentle than those on the moon.[23]
The Magellan probe used radar to photograph the surface of Venus.
Venus（♀），The equatorial radius is 6073 kilometers, 95% of the equatorial radius of the earth;The mass is about 81.5% of the earth.Venus is the only planet in the solar system whose rotation direction is opposite to the revolution direction.The revolution period is only 224.7 days, while the rotation period is 243.02 days, that is, Venus's "one day" is longer than its "one year".The surface of Venus is 70% plain, 20% depression, and about 10% highland, but the highest peak can reach 11270 meters, and 85% of the surface isbasaltOverwrite.Surface atmospherecarbon dioxideIt has an absolute advantage (about 97%). The surface temperature exceeds 400 ℃, the atmospheric density is 100 times of the earth's atmospheric density, and the pressure is about 90 times of the earth's surface.Beyond the dense atmosphere, there are 20 to 30 kilometers thicksulphuric acida bank of clouds.Venus has an iron core with a diameter of 3000 kilometers inside and a thick and hard shell on its surface.[24]
Venus has transits. It takes two transits as a group. The interval between the two transits is 8 years, but the interval between the two groups is more than 100 years. Therefore, some people say that a person can only see two transits of Venus in his life.[25]
The Earth (⊕) is a rotating ellipsoid planet.The equator has a radius of 6378 kilometersPolar radius6357 km is the only known planet in the universe that is still undergoing geological activities and has life.The earth has a uniqueHydrosphereAnd the observed plate structure.The earth's early atmosphere was not suitable for living things. After the Great Oxidation Event, the oxygen content in the atmosphere rose rapidly, so that living things could grow and multiply.[26]It has only one satellite, the moon;The moon is also the only known terrestrial planetLarge satellite。The earth revolves (the sun) for about 365 days, and rotates for about 1 day.At the beginning of January every year, the Earth and the sun are closest, with a distance of 147.1 million kilometersPerihelion。At the beginning of July, the Earth was the farthest away from the sun, about 152.1 million kilometers awayApohelion。The average distance between the sun and the earth is 149.6 million kilometers[27], this number is determined as an astronomical unit.MoonIt is the only natural satellite on earth.
Mars（Mars）（♂），To the naked eye, it is a striking bright red star.Seen from the earth, Mars sometimes goes forward and sometimes goes backward.There are many similarities between Mars and the Earth. Compared with the Earth, Mars is much smaller. Its equatorial radius is only 3397.2 kilometers, its mass is only 11% of the Earth's, and its orbit semi major axis is 1.5237 astronomical units.The revolution period is 686.98 days,fixed starThe day length is 24 hours and 37 minutes.The atmosphere of Mars is dominated by carbon dioxide, and the atmospheric density is onlyEarth's atmosphereThe density is 1%, which makes Mars often in a low temperature state. The average surface temperature is only minus 63 degrees Celsius, and the lowest temperature is minus 123 degrees Celsius.There is also a polar cap on the two levels of Mars.
The surface of Mars is covered with red soil and rocks.Due to the action of wind and sand, the surface of Mars is full of sand dunes, as well as terrain similar to river beds.This riverbed terrain is distributed in the southern hemisphere and near the equator, indicating that there were rivers and "water" flows on Mars about 3 billion years ago, just like on the earth today.The surface of Mars is desolate and red.Scattering of fine dust in the atmosphere makes the sky orange red.Martian soil contains a large amount offerric oxide, due to long-term exposure to ultraviolet light, the surface has formed a layer of red and yellowoxide。The whole Mars is a rusty world.[28]
The asteroid belt is distributed between the orbits of Mars and Jupiter, within the range of 2.3AU to 3.3AU from the sun.It is considered to be a failed planet that cannot be condensed into shape due to the gravitational interference of Jupiter, and it is the material left behind by the formation of the solar system.[29]The asteroid belt contains thousands or even millions of small objects with a diameter of more than one kilometer.However, it is estimated that the total mass of the asteroid belt will not exceed one thousandth of the Earth.The asteroid belt is very open, and the probe can fly safely.[30]The main celestial bodies are CeresVesta, Wisdom Star, etc.In addition to the small bodies in the asteroid belt, there are many different types of asteroids in the inner solar system (mainly classified according to the distribution of orbits and positions), such as Apollo asteroids,Aten asteroid , Amor asteroid, Troy asteroid, etc.The picture on the right shows the distribution of these asteroids.
Dawn spacecraft photographed the edge of the Ugadama crater in the southern hemisphere of Ceres.
Ceres, the smallest and only dwarf planet in the solar system in the asteroid belt.fromItalyastronomerPiazzi It was discovered and published on January 1, 1801.Ceres is probably a differentiation planet with a rock core,mantleThe layer contains a large amount of ice water material, and a large amount of water carrying minerals have been detected on the surface of the planet.In 2017,Dawn The detector found that,CeresThe crust is composed of ice, salt andhydrateThis crust represents the characteristics of most ancient oceans.A study suggests that Ceres has a soft and deformable stratum under its hard surface crust, which may be a sign of the residual liquid left by the ancient ocean.[31]
Jupiter's atmosphere captured by the Juno Jupiter probe.
JupiterJupiter (♃), with a diameter of about 143000 kilometers, is 11.25 times the diameter of the Earth, 1316 times the volume of the Earth, and 2.5 times the mass of all other planets.The average density of Jupiter is quite low, only 1.33g/cm3.It revolves around the sun for about 12 years, while its rotation lasts only 9.9 hours.[21]Because it rotates too fast, resulting in the flattening of the star, its equatorial radius differs from the polar radius by as much as 5000 kilometers.Jupiter has no solid shell. It is aLiquid hydrogenA liquid planet.The interior of Jupiter is a solid core composed of iron and silicon, called the Jupiter core, with a temperature of up to 30000 ℃.The outer part of Jupiter's core is mostly hydrogen. The liquid hydrogen molecular layer and the liquid metal layer are called Jupiter's mantle.Outside the Jupiter's mantle is the atmosphere of Jupiter, which is 1000 kilometers thick and almost composed of hydrogen and helium, with only a small amount ofmethane, ammonia and water vapor.Jupiter's Great Red Spot Methane in Jupiter's atmosphere can absorb ultraviolet rays.There are also very strong and frequent lightning phenomena in Jupiter's atmosphere, about 250 times a year on average.Jupiter has a dense atmosphere, with a series of alternating light and dark cloud bands parallel to the equator. The bright ones are called bands, and the dark ones are called bandsBanded pattern。Among them, the most striking is the Great Red Spot located in the southern tropics of Jupiter, which is egg shaped, 20000 km long and 11000 km wide.Jupiter's surface temperature is very low, only minus 148 ℃.[32]Jupiter has 79 satellites,[33]The four biggest ones areGanymede、Ganymede、Io, andEuropaGanymede is larger than Mercury and is the largest satellite in the solar system.
Saturn(Saturn) (♄), whose diameter is about 120000 kilometers, 9.5 times the size of the Earth, is second only to Jupiter;Its volume is 730 times that of the earth.Its average density is smaller than that of water, only 0.7g/cm3.If Saturn is put into water, it will float on the water.The internal structure of Saturn is similar to that of Jupiter, but it also has a rocky core.Outside the core are 5000 kilometers of ice andMetallic hydrogenComposed shell.Outside, like Jupiter, it is surrounded by colorful cloud bands.These colorful cloud bands are mainly composed of hydrogen, helium and methane.ifJupiterThe atmospheric motion is changeable, so Saturn's atmospheric motion appears calm, simple and fast.The jet stream on the surface of Saturn can reach more than 400m/s at the highest speed.The real surface of Saturn is invisible, but its cloud top, its temperature is below - 200 ℃.[34]
Saturn captured by the Hubble Space Telescope.
Saturn has 82 satellites, which is the largest planet in the solar system (October 2019).[33]titanLarger than Mercury, it is the only satellite in the solar system that actually has an atmosphere.Outside Saturn, there are countlessSmall satelliteOr seven rings made of ice, of which ring AB ring, andC-ringMain ring,D-ringAnd E ring areDark ringF ring and G ring were not discovered until 1979.The overall shape of Saturn's ring is similar to a hugeCompact disc, stretching from the top of Saturn's cloud to 320000 kilometers away.The color of the halo is reddish brown from a distance. In fact, each layer is slightly different. Ring C is blue, the inner layer of ring B is orange, the outer layer is green, and ring A is purple,Cassini division It's blue.[34]
Uranus(Uranus) (♅), about 2.9 billion kilometers away from the sun, 65 times the size of the Earth, second only to Jupiter and Saturn, ranking third in the solar system;Its diameter is more than 50000 kilometers, four times the size of the earth, and its mass is about 14.5 times the size of the earth.The semimajor axis of Uranus's orbit is 19.19 astronomical units, with a revolution period of 84 years.The inclination of the orbit to the ecliptic plane is only 0 ° 46 'Equatorial surfaceThe inclination to the track surface is 97 ° 55 '.In other words, itsAutorotation shaftIt almost falls on its orbital plane and moves around the sun in a lying position.Its star has a day length of about 16 hours and 48 minutes, but only the area between the north and south latitudes of 8 ° has the diurnal change due to rotation. The area above the latitude of 8 ° changes one day and night with a period of 42 years.
The faint halo of Uranus captured by Voyager 2.[35]
Uranus is basically composed of rocks and ice. The main components in the atmosphere arehydrogen（83%）、helium(15%) and a large amount of methane (2%).Uranus has 20 rings, but it is not very bright.[35]Uranus has 27 known moons, and the largest ones areTitania 、Tianwei IandTianwei Five。[36]
Neptune in Voyager 2.In the middle is its big black spot: a strong storm system.
Neptune(Neptune) (♆) is aGaseous planetAlthough it has a stone core with a mass similar to that of the earth, it is mainly composed of ice crust and gas.The equator has a radius of 24766 kilometers, which is close to 4 times the equator radius of the earth, 57 times the volume and 17.22 times the mass of the earth.The semi major axis of the orbit is 30.0579 astronomical units, making it the planet farthest from the sun.The included angle between the track surface and the ecliptic surface is also very small, less than 2 °.The atmosphere is mainly composed of hydrogen and helium, with a small amount of methane.The atmosphere changes frequently, with many cyclones and large storms, and the maximum storm speed can reach 2000 kilometers per hour.Neptune has five rings, but all are dim.The surface temperature is usually below - 200 ℃.Neptune has discovered 14 satellites so far (2019), including 7 internal satellites and 7 external satellites.maximalTriton There are still active geological activities and eruptionsLiquid nitrogenOfGeyserIt is also the only large retrograde satellite in the solar system.In the orbit of Neptune, there are some 1:1Track resonanceAn asteroid of the Troy type that forms Neptune[37]。Neptune is a planet calculated by mathematics.
The Kuiper belt is composed of a large number of debris, similar to the asteroid belt, but the main component of the composition is ice.It extends between 30AU and 50AU from the sun, and is estimated to contain dwarf planets hundreds of meters to several kilometers in diameter.It is estimated that there are 100000 small objects with a diameter of more than 50 kilometers in the Kuiper Belt, but the total mass of the Kuiper Belt is only one tenth or even one percent of the Earth.[38-39]
The Kuiper belt can be roughly divided into two parts: the resonance belt (celestial body) and the traditional belt (celestial body). The resonance belt is composed of celestial bodies that have resonance relations with the orbit of Neptune (for example, when Neptune rotates the sun three times, it circles the sun twice, or when Neptune rotates two times, it only circles the sun once).The traditional belt is an object that does not resonate with Neptune and is scattered within 39.4 to 47.7 astronomical units.[40]Their orbitalEccentricityLower.[41]The main celestial bodies are PlutoBird God Star, Chuangshen Star, etc.[42]
New Horizons color enhanced picture of Pluto.
PlutoPluto is a typical representative of dwarf planets, located in the Kuiper Belt.From 1930 to 2006, Pluto has long been regarded as theThe ninth planet, then in 2006International Astronomical UnionIs redefined as a dwarf planet.[43]Pluto has an equatorial radius of 1160km, a density of 1.5g/cm3, a mass only 0.24% of the Earth's, and a star day of 6 days, 9 hours, 21 minutes and 36 seconds;The semi major axis of the orbit is 39.5 astronomical units, the revolution period is 247.9 years, and the revolution direction is opposite to the rotation direction.Pluto is better than the moon, Io to GanymedeGanymedeAnd Triton and other satellites are still small.Pluto's orbit is abnormal, sometimes it is closer to the sun than Neptune, and the equatorial plane is almost at right angles to the orbital plane.The stars may be composed of rocks (70%) and ice (30%). The atmosphere is extremely thin, with nitrogen as the main component and a small amount ofcarbon monoxideAnd methane, and probably only at perihelion.Charon It is the largest moon of Pluto.Because the common center of mass of the orbit of Pluto is outside the surface of both, it is sometimes described as a conjoint system.Pluto also has four moons orbiting the system.
The discoverer of Pluto is an American astronomerClyde William Tombaugh。In February 1930, Tang Bo was studyingGeminiA flashing star was found in an area of.After tracking for nearly a month, on March 13, 1930, he finally announced that he had discovered this new planet, andRoman mythPluto in.July 14, 2015, USA“New Horizon No”The detector flew over Pluto, becoming the first detector to visit Pluto.The ashes of Tombaugh, who was carried on the New Horizon, also arrived at Pluto.NASA commemorates the discoverer of Pluto in a special way.[44]
Discrete discIt overlaps the Kuiper Belt, but extends outward into more space.In the early process of the formation of the solar system, the outward migration of Neptune causedGravitational disturbanceSome celestial bodies are thrown from the Kuiper Belt into the repeatedly uncertain orbit, thus forming a discrete disk (celestial body).The perihelion of most ecliptic discrete objects is within the Kuiper belt, but the aphelion can be as far as 150 astronomical units, and their orbits also have a great inclination to the ecliptic plane, even perpendicular to the ecliptic plane.Some astronomers believe that the ecliptic discrete objects should be another part of the Kuiper Belt, and should be called "Kuiper Belt discrete objects".
Eris (Xena) is a discrete disk object.Its mass is 25% larger than Pluto[45], and has a similar diameter to Pluto.It is the most massive dwarf planet known.Its orbit has a high eccentricity. The perihelion is 38.2AU away from the sun (about the average distance from Pluto to the sun), and the aphelion is 97.6AU away from the sun. It also has a great tilt to the ecliptic.
Comet isUniversal gravitationA class of objects with very small mass that move around the sun under the action of the sun are small objects in the solar system.Comets are mostly composed ofCometary nucleus、Comet、clouds that look like dust swept by a broomandCometary tailform,nucleus Nearly spherical, it is the dense and bright part of the comet's head, which is composed of ice, methane, ammonia and dust.The Huifa is distributed around the Huike, in the form of spherical clouds with a radius of hundreds of thousands of kilometers, and is composed of gas and dust.Huiyun is surrounded by Huifa, with a diameter of about 1-10 million kilometers, mainly composed ofhydrogen atomform.Huihe, Huifa and Huiyun are collectively called Huitou. Huiwei is the tail of the Huihe which is one hundred to two hundred million kilometers away from the sun. It is composed of dust and gas thrown by the Huihe under the action of the solar wind.
According to the distance of the comet's aphelion, the comets can be divided into four families, namelyJupiter family, Saturn, Uranus and Neptune.The return period of Jupiter family comets is 3-10 years, and there are 61 known comets;The return period of Saturn family comets is 10-20 years, and there are 8 known comets;The return period of Uranus family comets is 20-40 years, and there are 3 comets;Neptune family comets have a return period of 40-100 years, and there are 9 known comets.By 2020, more than 1600 comets have been found, of which more than 600 have been accurately calculated, but this is only a small part of comets.It is estimated that there should be at least 1.7 million comets within the orbit of Neptune, and at least 100 billion comets with a return period of 40000 years.
Comet Hale Bopp has two beautiful blue and white tails.
Comet Hale BoppIt's aLong-period comet, passed the perihelion on April 1, 1997.July 23, 1995Alan Hale Alan Hale and Thomas Bopp found the comet independently.This comet has a light intensity of - 1.4 when passing the perihelion, which can be seen with the naked eye even in the city. It is the brightest comet since 1975, and therefore it has become one of the most spectacular comets in the past 20 years.According to HubbleSpace telescopeHale Bopp comet is a large comet with a diameter of about 40 kilometers.After preliminary calculation,Comet Hale BoppIt will return in more than 2000 years.[46]
Schematic diagram of heliosphere and interstellar space and their interactions.[47]
The heliosphere isSupersonic velocityWhen the solar wind expands outwardInterstellar mediumThe huge "bubble" space formed by the interaction is mainly controlled by the magnetic field and plasma from the sun.Beyond the top of the heliosphere is the vast interstellar space,[48]Full ofPlasma、Neutral atom, dust and other interstellar media.The boundary layer formed by the "two armies against each other" between the solar wind and the interstellar medium has blocked the invasion of high-energy cosmic rays, and is the outermost "city wall" of the Earth's home.Nevertheless, some interstellar neutral components can still enter the heliosphere and be captured by the solar wind, thus changing the structure and dynamic characteristics of the heliosphere.[47]
The maximum distance of solar wind transmission is about 95 astronomical units, which is three times the orbit of Pluto.Here is the place where the solar wind and the interstellar medium collide and shock each other.The solar wind slows down, condenses and becomes more chaotic here, forming a huge oval structure, which is calledheliosheath , looks and behaves likeCometary tail, in the direction of constantStellar windThe direction of extends outward for about 40 astronomical units, but the tail end of the opposite direction extends several times this distance.The outer edge of the solar circle is the heliosphere top, where the solar wind ends, and the outer space is the interstellar space.
The shape and form of the outer edge of the solar circle are likely to be affected by the interaction with interstellar matterfluid dynamicsAt the same time, it is also affected by the dominant solar magnetic field at the southern end;For example, its shape isNorthern HemisphereIt has expanded 9 astronomical units (about 1.5 billion kilometers) more than the southern hemisphere.Beyond the heliosphere top, at about 230 AU, there areBow shock, it is when the sunGalaxyIt is generated when traversing.
The Oort cloud is a spherical cloud, ranging from about 50000 AU (about 1 light year) away from the sun to 100000 AU (1.87 light years).There are up to 1 trillion icy objects here, and they are considered to be the source of all long-period comets.It is believed to be composed of comets expelled from the inner solar system by the gravitational action of outer planets.AltevianCelestial motionVery slow, and may be perturbed by rare events, such as collisions, passing stars, orGalactic tideGravitational effect, etc.[49]In 2018, the most distant and larger object known is2018 VG18, about 120AU from the sun.[50]Ordinarily, the Oort cloud is considered to be the boundary of the solar system.This may change as humans become more aware of the Oort cloud.[51]
Dim blue dot: Voyager 1 saw the Earth from 6 billion kilometers away.
Exoplanet
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On July 8, 2022 local time, NASA（NASA）The first list of objects photographed by the James Webb Space Telescope (JWST) was released, including galaxies, nebulae and extrasolar giant planets.WASP-96b is a giant planet outside the solar system, mainly composed of gas.The planet is nearly 1150 light-years away from the Earth and rotates around its star once every 3.4 days.Its mass is about half that of Jupiter。[53]
