Planet (English: Planet), usually refers to the fact thatluminescence, aroundfixed starA moving celestial body.Its revolution direction is often the same as that aroundfixed starThe rotation direction of is the same.
Generally speaking, planets need to have certainqualityThe mass of a planet should be large enough and approximate to the shape of a sphere, and it cannot occur like a star itselfNuclear fusion reaction。Planets begin with microscopic particles of sand or ash like dust.[7]
In history, the names of planets come from the fact that their positions are not fixed in the sky, just like they walk in the sky.In the solar systemnaked eyeFive visible planetsMercury、Venus、Mars、JupiterandSaturnIt has been discovered by human beings as early as prehistory.In the 16th century,Heliocentric theoryReplacedGeocentric theoryHuman beings have learned that the earth itself is also a planet.
Latest discovery: the hottest planet WASP-33b
The telescope was invented andUniversal gravitationAfter being discovered, human beings discoveredUranus、Neptune、Pluto(has been reclassified asdwarf planet）There are many asteroids.At the end of the 20th century, human activities outside the solar systemStellar systemPlanets have also been discovered in China. As of May 8, 2016, human beings have discovered 2125 extrasolar planets.
definition
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How to define the concept of planets has always been a controversial issue in astronomy.International Astronomical UnionOn 24 August 2006, the General Assembly adopted a new definition of "planet", which includes the following three points:
1. Must be around a star[5]A moving celestial body;
2. The mass must be large enough to overcome the gravity of solids to achieveHydrostatic balanceThe shape of (nearly a sphere);
3. The asteroid in the area near the orbit must be cleared,revolutionThere can be no object larger than it within the orbital range.[1]
history
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From the sacred wandering stars in the classical era to the real entities in the scientific era, people's understanding of planets is evolving constantly with history.The concept of planets has been extended not only to the solar system, but also to other extrasolar systems.The inherent ambiguity of the definition of planets has led to many scientific debates.
fromremote dateSince then, five classic planets visible to the naked eye have been known to peoplecosmologyAnd ancient astronomy.In ancient times, astronomers recorded how certain points of light moved across the sky relative to other stars.The ancient Greeks called these light spots "pi"λάνητες ἀστέρες”(i.eplanetes asteres, or simply called "πλανήτοι”（planētoiThe English name "planet" evolved from this.
In ancient Greece, China, Babylon and virtually all pre modern civilizations, people almost universally believed that the earth was the center of the universe, and all "planets" revolved around the earth.The reason for this understanding is that people see stars rotating around the earth every day, and it seems to be common sense that the earth is solid and stable, and should be stationary rather than moving.
In April 2023, Webb telescope will be usedThe composition of planet formation has been detected around hundreds of young stars in the Magellanic Cloud.[7]
In May 2023, the research team of Massachusetts Institute of Technology reported the process of a planet (ZTF SLRN-2020) or being "swallowed" by the host star。[8]
planets
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survey
Generally speaking, the diameter of the planet must be more than 800 kilometers and the mass must be more than 500 million tons.
Mercury
According to this definition, as of 2013, there are 8 planets in the solar system, namely:Mercury（Mercury）、Venus（Venus）、earth（Earth）、Mars（Mars）、Jupiter（Jupiter）、Saturn（Saturn）、Uranus（Uranus）、Neptune（Neptune）。
The Planetary Definition Committee of the International Astronomical Union said that it could not be ruled out that there would be more qualified celestial bodies listed as planets in the solar system in the future.There are more than 10 objects in the solar system that may meet the definition of planets on the astronomers' observation list.
Visible planets
A planet is a celestial body that does not emit light of its own and orbits a star.Generally speaking, planets need to have a certain mass. The mass of a planet should be large enough that its shape is about a round ball. Those with insufficient mass are called asteroids.The name "planets" comes from the fact that their positions are not fixed in the sky, as if they were walking.
Planet and New Horizon
The five planets visible to the naked eye in the solar system are:Mercury、Venus、Mars、Jupiter、Saturn。After thousands of years of exploration, to the 16th centuryCopernicusAfter the establishment of the heliocentric theory, it was generally recognized that the earth is one of the planets that revolve around the sun, andplanetsIt forms aPlanetary system——A major member of the solar system.Planets themselves generally do not emit light, but shine by reflecting the light of stars on their surfaces.In the sky background mainly composed of stars, the planets have obvious relative movement.The planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The eight planets can be divided into three categories according to the origin of the planets in different forms:terrestrial planet(including water, gold, earth and fire)Giant planet(wood, soil) andApohelion(Tianwang, Haiwang).The movement of planets around stars is called revolution, and the orbits of planets have three characteristics: coplanarity, isotropy and near circularity.The so-called coplanarity means that the orbital planes of the eight planets are almost in the same plane;Homotropism means that they revolve around the star in the same direction;Near circularity means that their orbits are quite close to circles.
Around some planets, there are material rings running around the planets, which are composed of a large number of small objects (such as rocks,iceBlock, etc.), which is bright due to reflected sunlight, and is calledPlanetary ring。Before the 1970s, people thought that Saturn alone had rings. Later, Uranus and Jupiter also had rings, which provided new information for the study of the origin and evolution of the solar system.
earth
Satellites are celestial bodies orbiting planets, and the moon is the satellite of the earth.Satellites reflect sunlight, but except the moon, the reflection of other satellites is very weak.Satellites differ greatly in size and massKinematic characteristicsIt is also very inconsistent.
In the solar system, with the exception of Mercury and Venus, other planets have different numbers of satellites.Between Mars and Jupiter, there are hundreds of thousands of asteroids of different sizes and shapesElliptical orbitMoving around the sun, this area is calledAsteroid belt。In addition, there are manycometAs for floating in the interplanetary spacespaceOfMeteoroidIt is even more impossible to count.
Although there are many kinds of celestial bodies in the solar system, none of them can compare with the sun.The sun is the source of light and energy in the solar system, and also the largest celestial body in the solar system. Its radius is aboutEarth radius109 times, or 1.8 times the distance between the earth and the moon.The mass of the sun is 330000 times larger than that of the earth, accounting for 99.9% of the total mass of the solar systemQuality CenterIt controls all the celestial bodies in the solar system tightly around it with its powerful gravity, making them inseparable and rotating around itself orderly.At the same time, the sun, as an ordinary star, leads its members around foreverGalaxyThe center of the.
As the name implies, many characteristics of Earth like planets are close to the Earth. They are relatively close to the sun, with small mass and radius, and large average density.
Earth like planets have a layer on their surfacesilicateThe hard crust composed of rock like rocks has various types similar to the earth and moonGeomorphic features。For a planet without atmosphere (such as Mercury), its appearance is similar to the moon, and it is densely covered withCraterAnd grooves;For Venus with a dense atmosphere, its surface topography is more like Earth.
Planets have been discovered by humans since prehistory. Later, humans learned that the earth itself is also a planet.
Study rock and soil for evidence of how water affects Mars
two thousand and six
U.S.A
Mars Reconnaissance Orbiter
Pay attention to the weather changes on Mars and look for signs of water
Neptune
Other planets
Giant planets and apogee planets:
JupiterandSaturnIt is the giant of the planet world, called a giant planet.They have denseatmosphereUnder the atmosphere, there is no solid surface, but a piece of boilinghydrogenThe "vast ocean" is formed.So they are essentiallyLiquid planet。Uranus、NeptuneThese two distant planets, called apogee planets, were discovered after the invention of the telescope.They have an atmosphere mainly composed of molecular hydrogen, usually with a very thickMethane ice, ammonia ice and other ice materials cover the surface, and then the hard rock core is below.According to the above definition, Pluto has lost its planetary status.
Pluto, the last of the nine planets in the solar system for more than 70 years, has been controversial since its discovery.After years of controversy in the astronomical community and several days of quarrels at the current IAU General Assembly, Pluto was finally "demoted" and expelled from the planet family.From then on, this celestial body wandering on the edge of the solar system can only be called together with other "brothers and sisters" of similar size“dwarf planet”。
Saturn, the planet with halo
On August 24, 2006, according to the new definition adopted by the General Assembly of the International Astronomical Union at 11:00, "planet" refers to a planet that revolves around the sun and has enough gravity to overcome itRigid strengthThe celestial body that makes the celestial body spherical and can clear the area near its orbit.According to the new definition, the planets in the solar system will include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, all of which were discovered 1900 years ago.
According to the new definition, the celestial body with enough mass and spherical shape but unable to clear other objects near its orbit is called“dwarf planet”。Pluto is a dwarf planet.Other objects that revolve around the sun but do not meet the above conditions are collectively referred to as the "solar systemSmall bodies”。
Since August 24, 2006, the new solar systemplanetsThey are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
New astronomical discoveries have constantly challenged the traditional concept of "nine planets".Astronomers have discovered some differences between Pluto and other planets in the solar system.Pluto is in an orbit outside Neptune, belonging to the outer solar systemKuiper This region has always been the birthplace of asteroids and comets in the solar system.
Since the 1990s, astronomers have found thatKuiper belt（Keper belt）There are more large bodies orbiting the sun.For example, the American astronomer Brown found that“2003UB313”Is an object whose diameter and mass exceed Pluto.
Uranus
dwarf planet
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Under the new planet standard, the Planetary Definition Committee has also determined a new secondary definition -“Pluto like”。This refers to the planets that orbit outside Neptune and revolve around the sun for more than 200 years.After 12 pieces meet the new definitionSolar system planetsPluto, "Charon" and "2003UB313" (Zina/Zishen) are all "dwarf planets".
Astronomers believe that“dwarf planet”The orbit ofEccentricityLarge oval.The origin of such planets may be different from other planets in the solar system.With the improvement of observation methods, astronomers may find more large objects at the edge of the solar system.If the list of planets in the solar system continues to expand in the future, "dwarf planets" will also be added.
Cause
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Planets are formed with stars.
CosmicNebulaKnown as "star building workshops", they are celestial bodies gathered by a large number of interstellar dust and other materials.When the nebula is disturbedInterstellar dust、Molecular cloudThe balance between the nebular matter will be broken, the nebular matter will converge due to gravity, and the dust at the center of gravity will be subjected to more and more pressure. At the same time, the gravitational potential energy will be converted into thermal radiation to delay this convergence process (this process is calledaccretion ）。However, as the accumulated dust becomes thicker and thicker, the thermal radiation cannot be effectively scattered into the space, which will make the temperature of the central part become higher and higher, and finally reach the critical temperature of nuclear fusion.At this point,ProtostarThus, the impact generated in the instant of nuclear fusion will block the process of protostars obtaining nebular material from the nebula (i.e., accretion process).[2]
Many newly formed stars are surrounded by“Protoplanetary disk ”It contains all the material that will form the future star system.A typical protoplanetary disk comes from a molecular cloud mainly composed of hydrogen molecules.When the molecular cloud reaches the critical mass or density, it will collapse due to its own gravity.When the cloud begins to collapse, the density will become higher. The molecules originally moving randomly in the cloud will also show the average direction of net angular momentum movement of the nebula. The conservation of angular momentum will lead to the reduction of the nebula while increasing its rotation speed[3](The protoplanetary disk is regarded as the rotation of a whole, which can also be understood as the revolution around the protostar).This rotation also causes the cloud to flatten gradually. When it is combined with the protostar, it looks like a pocketed egg.
The protoplanetary disk is the cradle of planets in this young stellar system.In the process of rotation, the protoplanetary disk will also converge due to gravity, but this convergence process is mainly centered on the dust in the protoplanetary disk.The new sky formed by convergence will attract other molecular clouds and dust near its orbit, which will become larger and larger until there is no matter near its orbit for its growth.[4]This process is called "clearing the area near its orbit" in the definition of a planet.
The formation process of the above planets will occur simultaneously in different regions of the protoplanetary disk (the "simultaneity" on a cosmic scale, that is, the interval does not exceed hundreds of thousands of years), so that one to several planets and many asteroids with failed promotion planets will be bred in the protoplanetary disk.The protoplanetary disk will eventually either become the nourishment for the growth of planets or be blown out of the galaxy by the strong stellar wind of young stars, thus completing its mission.
Related disputes
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Shortly after the publication of the new definition of a planet, 12 astronomers issued a "petition against Pluto's demotion", questioning the way hundreds of astronomers voted to demote Pluto.According to Article 3 of the new planet definition, the Earth may also be expelled.
Petition against Pluto's demotion
12 astronomers published a petition against Pluto's demotion in the online edition of Nature
On August 31, 2006, 12 astronomers jointly published the Petition to Protest Pluto's Degradation in the online edition of the British journal Nature, seriously questioning the practice of hundreds of astronomers to let Pluto leave the "planet throne" by voting.Astronomers also said that the definition of new planets at the 26th International Astronomical Union was not completely accurate.
It is said that only 5% of the world's astronomers voted, and some experts said that "this is a hasty resolution".
It is understood that the 26th IAF lasted for 10 days. Many experts left before the final vote due to financial problems. Only a few hundred experts actually participated in the vote on Pluto's status, which was questioned by the joint petition astronomers.In the petition, these scientists pointed out that the number of astronomers who voted at the Prague Conference only accounted for less than 5% of global astronomers.It is not convincing to make such a big decision with such a proportion.
These 12 signed astronomers include NASA“New Horizons ”Alan Stern, the person in charge, Mark Sykes of the American Academy of Planetary Sciences, etc.They also proposed that astronomers who opposed Pluto's demotion continue to sign the petition.Alan Stern said in an interview with the media: "The debate on this issue will not stop because of the resolution on the 24th. There are more than 2500 members of the International Astronomical Society from 75 countries, and only 300 people participated in the voting. This is a hasty resolution, a bad science. Everything is not over."
Using dynamic criteria to define planets will cause new problems
Just returned from this conferenceBeijing PlanetariumCurator Dr. Zhu Jin introduced to our reporter that an important decision of the International Astronomical Union was to divide planets and other celestial bodies in the solar system into three different categories to define them.
There are three requirements for the definition of planets: one is to be in the orbit around the sun;Second, it has enough mass to make its surface reach the shape of hydrostatic equilibrium (nearly spherical);Finally, the area near its orbit has been cleared.Only eight planets discovered 1900 years ago met these requirements.
Compared with the improper voting procedure, the scientists who participated in the petition could not accept the new definition of planet.
As for the second definition of a planet, the petitioner believes that the new definition uses dynamics rather than the characteristics of matter itself, which is a necessary condition to decide whether or not to become a planet.And this result will affect the definition of other astronomical systems, such as stars, galaxies, nebulae and even asteroids.Because in the definition of these systems, dynamics is not the decisive factor.
Earth may also be expelled
According to Article 3 of the new planet definition, the Earth may also be expelled.
These astronomers pointed out that if according to Article 3 of the new definition, planets such as Earth and Jupiter do not meet the definition and will also be "expelled".The third article of the new definition says that a planet must have enough gravity to clear the area near its orbit.According to this definition, there are many asteroids between the orbits of Earth, Saturn and Jupiter, so they cannot be considered as "clearing the area near the orbit".
In addition to these signed astronomers, Jay Pasackoff, an astronomer from Williams University who attended the voting meeting, also insisted that Pluto is a planet.He said: "The spirit of this conference is to standardize future scientific discoveries and behaviors, but it should not be a negation of the past."
Lowell Observatory Director Millis also said that he hoped to add new planets, rather than exclude Pluto.
Relevant definitions
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Definition of dwarf planet
one
Natural celestial body
two
Orbiting the sun (star)
three
Its own gravity is enough to overcome its rigid force to make the celestial body appear spherical (to achieve hydrostatic balance)
four
No ability to clear other objects near its orbit
five
Not a satellite
Those in the solar system that meet this definition include:
Asteroids are similar planets in the solar system that move around the sun, but are much smaller in volume and mass than planets.
So far, about 700000 asteroids have been found in the solar system, but this may be only a small part of all asteroids, and only a few of these asteroids have a diameter of more than 100 kilometers.By the 1990s, the largest asteroid was CeresKuiper beltSome asteroids found in Kuiper Belt are larger than Ceres in diameter. For example, Varuna, which was found in 2000, has a diameter of 900 kilometers and was found in 2002Quaoar (Quaoar) is 1280km in diameter, and the diameter of 2004 DW discovered in 2004 is even 1800km.Discovered in 2003sedna （Asteroid 90377）It is located outside the Kuiper Belt, with a diameter of about 1500 kilometers.
It is estimated that the number of asteroids may be 500000.The largest asteroid is only about 1000 kilometers in diameter, while the micro asteroid is onlycobblestoneNormal size.
There are about 16 asteroids with a diameter of more than 240 kilometers.They are all located inEarth orbitInside to outside of Saturn's orbit in space.The vast majority of asteroids are concentrated in the asteroid belt between the orbits of Mars and Jupiter.Some of the asteroids' orbits intersect the Earth's orbit, and some have collided with the Earth.
Asteroids are remnants of the solar system.There is a speculation that they may be the remains of a mysterious planetremote dateEncountered a hugeCosmic collisionAnd destroyed.But judging from the characteristics of these asteroids, they do not seem to have gathered together.If all the asteroids are added together to form a single celestial body, its diameter is less than 1500 kilometers - smaller than the radius of the moon.
cometThe long, bright and sparse comets, except when far from the sunCometary tailIn the past, it gave people the impression that comets were very close to the earth, even within our atmosphere.1577TychoHe pointed out that comets did not show different directions when viewed from different places on the earth: therefore, he correctly concluded that they must be far away.Comets belong to small bodies in the solar system.Whenever a comet approaches the sun, its brightness increases rapidly.The observation of comets far away from the sun shows that they move along a highly elongated ellipse, and the sun is at a focus of the ellipseKepler's first lawagreement.Comets spend most of their time traveling far from the sun, where they are invisible.They can only be seen when they are close to the sun.About 40 comets have relatively short revolution periods (less than 100 years), so they appear one after another as the same celestial body.
The first object observed to appear in succession in history is Halley's Comet,NewtonHaley (1656-1742), a friend and benefactor of, realized that it was cyclical in 1705.Its cycle is 76 years.Historical records show that it has been observed every time it passes through the sun since 240 BC and possibly since 466 BC.It was observed to pass in 1986.The brightness of a comet is very low when it is far from the sun, and its spectrum is simply the spectrum of reflected sunlight.When a comet enters within 8 astronomical units from the sun, its brightness begins to increase rapidly and its spectrum changes sharply.Scientists saw several bright spectral lines belonging to known molecules.The reason for this change is that the solid materials that make up the comet（Cometary nucleus）Suddenly heated enough to evaporate and calledCometThe comet nucleus is surrounded by a cloud of gas.The ultraviolet light of the sun causes the gas to glow.The diameter of a comet is usually about 105 kilometers, but its tail is often very long, reaching 108 kilometers or 1 astronomical unit.
Scientists estimate that comets that are generally close to the sun and only a few astronomical units away will disintegrate within thousands of years.In 1066 AD, on the eve of the Norman invasion of EnglandHalley's CometRegression.At that time, people looked at this strange celestial body with a long tail in the night sky with complex feelings, thinking it was a war warning and prediction given by God.Later,the Norman Conquest In England, the wife of Norman commander embroidered the scene of Halley's Comet's return on a tapestry to commemorate it.Chinese people call comets“Broom star”、“Disaster star”。The appearance of comets and human wars, famines, floodsplagueThere are many things in Chinese and foreign history that are connected with disasters.Comet is a kind of small cloud like object with small mass that moves around the sun in a flat long orbit (very few in a near circular orbit).
Other celestial bodies
Ceres: It has a diameter of about 950 km, an average distance from the day of about 420 million km, and a revolution cycle of about 4.6 years.Originally belonged to the category of asteroids.
Zina: The astronomical number is 2003UB313, and Zina is its nickname. Its diameter is between 2300 and 2500 kilometers, the average distance from the sun is about 16 billion kilometers, and the revolution period is about 560 years.The newly discovered celestial body in 2003, due to its discoverycelestial bodies Debate over classification (since Pluto is a planet, Zina should be the tenth largest planet in the solar system).
Charon: It has a diameter of 1200 kilometers, revolves around Pluto, and its revolution period is equal to Pluto's rotation period of 6.4 days.Although the diameter of Charon is larger than Ceres, it is a satellite of Pluto (Pluto and Charon rotate around a point, so Charon is also the companion of Pluto.), so it does not belong to the scope of dwarf planets.
Planetary index
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Definition of planetary index
Planetary index refers to the parameter used to characterize the strength of planetary field potential, which is represented by X.
The ratio X can be used to classify celestial bodies and estimate the central temperature of planets and themagnetic field intensityIt can judge whether there is atmosphere and water on the celestial body.
Planets mean they can't happenThermonuclear reactionThe celestial body ofPlanetary indexX is greater than 0.00177525.According to the size of the planetary index, it can be subdivided into:Brown dwarf、Giant planet, main planet, dwarf planet, asteroid and meteorite.according tomotion state Different from the location, it can also be subdivided into:（Regular planet/It can be any of the six planets in the previous category/satellite/It can be any of the six planets in the previous category/, and comets/mostly asteroids and meteorites in the six planets in the previous category/.
New pattern of the solar system
Planetary classification
According to this definition, up to 2010, there are 1 star, 4 giant planets, 9 main planets and 76 planets in the whole solar systemdwarf planet, a total of 90 large celestial bodies.But Pluto is still not the main planet.
Astronomers found that an exoplanet beyond the theoretical range
Astronomers found that there are defects in the theory of exoplanet formation, and the micro gravitational lens method will improve the observation of exoplanets to a higher level.
According to foreign media reports, with theKeplerWith the launch of the exoplanet probe, humans will find more exoplanets in the future, and more and more exoplanets will be found. Almost all newly published research results involve a problem: how these planets are formed.When astronomers found the first exoplanet, whether the theory of planetary formation in the solar system was also applicable to other galaxies, and whether the theory of planetary formation we know was only part of a framework, all these questions puzzled astrophysics.For example, there are a large number of hot Jupiter planets in the universe, but they are outside the scope of existing theories.
List of Big Celestial Bodies in the Solar System
This will lead scientists to re-examine the existing theoretical structure and return to the starting point for deduction. The biggest problem is: how many exoplanets are there in the universe, and how many loopholes are there in our planetary formation model?In response to these problems, scientists found that the reason for hindering the further discovery of exoplanets was the existence of problems in observation methods. The gravitational swing method used could only find exoplanets with large masses, and the orbits of these exoplanets must be close to the star system.
Although the most advanced Kepler exoplanet detector can improve the observation of exoplanets to a certain extent, and it is easy to find planets that are far away from the Earth and have low mass, it can only find planets that are close to the stars.However, there is a new technology for discovering exoplanets, namely gravitational microlens method. The mass of exoplanets discovered by this method can be reduced to 10 times the mass of the Earth, and the orbits of such exoplanets are also far away from their star systems.
According to this method, a team of astronomers published theRocky planetRange of.Search for laymanCatalogueAstronomers have discovered 13 exoplanets using the gravitational microlens method, the latest one is MOA-2009-BLG-266Lb. Through accurate calculation, it is found that its mass is only about 10 times that of the Earth, its orbit is 3.2 astronomical units (one astronomical unit is 150 million kilometers), and the mass of the star in its star system is only aboutSolar massHalf of.
A gaseous planet in a star system described by an artist
This new discovery is very important for the exploration theory of exoplanets.Because this is the first time that an exoplanet of this quality level has been found, scientists call it the "mass snow line". The orbital orbit corresponding to this mass determines whether the water on this planet is liquid water, and whether ammonia and methane will freeze into ice. If the orbital conditions for the existence of liquid water are met, it is very likely to breed extraterrestrial life.
However, this theoretical "mass snow line" is not a standard for measuring extraterrestrial life. If it is deduced to the formation period of the planet, it will make the planet form a hard nuclear structure. If it is beyond this range, astronomers estimate that the formation time of the planet will be relatively short. If it is further away from this range, the density of the planet will decline.
Therefore, according to this theoretical model of planetary formation, the standard formation mass will reach 10 times the mass of the Earth, and there will be a large accumulation of solid matter at the initial stage of formation. In this process, gas accumulation can be carried out at a slower level. If this process is too fast and the planetary material is accumulated too quickly, its atmospheric structure will become thick and collapse,The acceleration of this cycle will cause the planet to become a gaseous planet.
Whether this theoretical model of planetary formation can be widely applied still needs to be further combined with astronomical observation.By pairing and adjacencyPlanetary systemTo judge whether the theory conforms to the observation.It is particularly important to point out that from this theory, giant gaseous planets should not be observed around low-mass star systems, because the gas disk will disappear before the collapse of the planet's atmosphere leads to further accretion effects.What astronomers expected has been confirmed by the observation reports of more than 500 exoplanets discovered by Kepler exoplanet probe.
In addition, press this“Quality snowline”During the observation, more low-mass planets were also found, which also supported the hypothesis that the formation of planets would be prevented to a large extent if there were no solid matter formed at a lower temperature in the early stage of planet formation.At the same time, some new observation plans will be realized in the near future, such as the Optical Gravitational Lens Experiment IV (OGLE - IV) detector will be fully operational and the new generation of WISE Space Observatory will use more matureMicro gravitational lensConduct exoplanet observations.
Search method
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Astrometry
Astrometry is searchExtrasolar planetsThe oldest method.This method is to accurately measure the position of a star in the sky and observe how that position changes over time.If the star has a planet, the gravity of the planet will cause the star to move in a tiny circular orbit.In this way, stars and planets surround their commoncentroidRotate.Since the mass of a star is much larger than that of a planet, its orbit is much smaller than that of a planet.
Radial Velocity
The radial velocity method makes use of the fact that stars move in a tiny circular orbit under the action of planetary gravity. The goal is to measure the speed of stars moving towards or away from the Earth.according toDoppler effect, siderealApparent velocityFrom the starsSpectral lineThe movement of is derived.
Transit method
When the planet moves in front of the star, the light of the star will weaken accordingly.How much the light weakens depends on the size of the stars and planets.In the starHD 209458In the example of, its light is reduced by 1.7%.Astronomers discovered the planet of star HD 209458 by transit methodHD 209458b。
Pulsar Timing
Through observationPulsarTo infer the existence of planets.Generally speaking, the rotation period of a pulsar, that is, its signal period, is stable.If a pulsar has a planet, the pulsar signal period will change.
In September 2022,An international scientific research team has found two new planets only 100 light years away from the Earth, one of which may be suitable for life.These two planets are called "super earth", respectivelyLP 890-9bandLP 890-9c。[6]
In 2024, at a distance of about 1200 light years from the Earth, astronomers found a "super fluffy" exoplanet - WASP-193b. Its density is similar to that of cotton candy, and it is also the second brightest planet observed by humans so far, second only to Neptune like Kepler 51d.WASP-193b is about 50% larger than the nearby gas giant planet Jupiter, but its mass is only 0.14 of Jupiter by calculation, and its density is estimated to be about 0.059 grams per cubic centimeter.[9]
