Comet refers to enteringsolar systemInternal brightness andshapeCelestial objects that move around the sun and change with the distance between the sun, have a unique cloud like appearance.Comets are divided intoCometary nucleus、Comet、Cometary tailThree parts.The comet nucleus is composed of ice material. When the comet approachesfixed starWhen the comet material sublimatesIce coreHazyCometAnd a thin stripMaterial flowComet tail.becausesolar windThe tail always points away from the sun to form a long tail.Comet tails are generally tens of millions of kilometers long, and the longest can reach hundreds of millions of kilometers.Comet is like a broom, so it is commonly known asBroom star。The orbit of comets is mostly parabola orhyperbola, few areellipse。At present, more than 1700 comets have been found orbiting the sun.The famous Halley's Comet orbits the sun for 76 years.
February 21, 2014, JapankyotoThe research team of the University of Technology found the presence of ammonia on the comet.[2]According to the latest report, scientists have recently found some chemical residues belonging to the comet "67P/Chuliumov Graximenk" on the Rosetta spacecraft.Scientists use detectors to analyze these chemicals and find that their main components are ammonia, methanehydrogen sulfide、Hydrogen cyanideandformaldehyde。From this, scientists concluded that the smell of comets smells likeRotten egg、Equine urine、alcoholandThe bitter almondOfsmellcomprehensive[3]。
structure
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Comet has no fixed volume, it is far awaysunlightWhen, the volume is very small;When approaching the sun, the comet becomes larger and larger, the tail becomes longer, and the volume becomes very huge.Cometary tailThe longest distance can reach more than 200 million kilometers.The mass of the comet is very small, and the average density of the comet nucleus is 1 gram per cubic centimeter.CometAnd the comet tail are extremely thin, and their mass only accounts forTotal mass1%~5%, or even less.Comet material mainly consists of waterammonia, methaneCyanogen, nitrogen, carbon dioxide, etc., while the comet nucleus consists of water and carbon dioxide condensed into ice（dry ice）, ammonia and dustparticulateMixed composition, a "dirty snowball"
comet
The surface of the comet nucleus is composed of water condensed into icedry ice、dust、ammoniaandrockMixed.[4]
Generally, comets are composed of comet head and tail.The head of a comet consists of a nucleus and a coma.Later, since 1920, sounding rocketsArtificial satelliteandspacecraftThe close detection of comets found that some cometsCometIs covered with hydrogenatomSurrounded by giant clouds, they are called "comet clouds" or "hydrogen clouds".In this way, we can say that the comet head is actually composed of comet nucleus, comet hair and comet cloud.
The nucleus is the most central, essential and main part of a comet.It is generally considered as a solid, consisting of stone, iron, dust, ammonia, methane and ice.The diameter of the comet nucleus is very small, ranging from several kilometers to more than ten kilometers, and the smallest is only a few hundred meters.
Comet: It is a star like fog formed by gas and dust around the comet nucleus.The radius can reach hundreds of thousands of kilometers, and the average density is less thanEarth's atmosphereOne billionth of density.Through spectral and radio observations, it is found that the main components of the gas in the comet are neutral molecules and atoms, including hydrogenhydroxyl、oxygen, sulfurcarbon、carbon monoxide、amino, cyanogensodiumAnd other complicatedHydrogen cyanide(HCN) and methyl cyanide (CH ∨ CN).These gases flow out of the center at an average speed of 1-3 km/s.
Comet cloud: outside the comethydrogen atomThe cloud is also called hydrogen cloud.The diameter can reach 1 million to 10 million kilometers, but some comets do not have cometary clouds.
According to the shape and composition characteristics of comets, they can be divided into "non hair comets", bulb comets, anchor comets, etc.
The comet tail began to appear when the comet approached the sun about 300 million kilometers (2 astronomical units), and gradually grew from small to large to long.When the comet passes the perihelion (that is, the comet moves to the nearest point from the sun) and then moves away from the sun, the tail of the comet gradually becomes smaller until there is no tail.The direction of the comet tail is always extended away from the sun. When the comet approaches the sun, the comet tail is dragged behind. When the comet leaves the sun, the comet tail becomes the leader again.The comet tail is very large, but the material is very thin.There are also great differences in the length and width of comet tails. Generally, comet tails are between 10 million and 150 million kilometers long. Some are surprisingly long and can cross half the sky. For example, the tail of comet 1842 I is 320 million kilometers long and can reach from the sun toMarsTrack.Generally, the width of cometary tails ranges from 6000 to 8000 kilometers, with a maximum width of 24 million kilometers and a minimum width of 2000 kilometers.
According to the shape of comet tails and the size of solar repulsion, comet tails can be divided into two categories.One is "ionic comet tail", which is composed of ionic gases, such as carbon monoxide, hydrogen, carbon dioxide, carbon, hydrogen and othersionizationThe molecule of.This kind of comet tail is relatively straight, thin and long, so it is also called "gas comet tail" or type I comet tail.The other is“Dust comet tail”, is composed of fine dust, yellowphotonIt is formed by pushing away fine dust under the radiation pressure of.Comet tails are curved, and the wider ones are also called type II tails;However, the tail with sharp curve, short and wide is also called type III comet tail[8]。In addition, there is another kind called“Anomalous cometary tail”The tail of a comet is fan-shaped or spiky extending towards the solar system.Generally, a comet has more than two tails of different types.
Comets with elliptical orbits are also calledPeriodic cometThe other two orbits are also calledAperiodic comet。Periodic comets are divided intoShort period cometandLong-period comet。Comets generally consist ofCometary headandCometary tailform.Comet heads includeCometary nucleusandCometTwo parts, some andCometary cloud。Not all comets have structures such as nucleus, hair and tail.The shape of comets has been studied in ancient ChinaMawangduiThere are 29 paintings on the silk books unearthed from the ancient tombs of the Western Han DynastyComet chart。It is clearly stated in the Jin book Astronomical Records that comets do not emit light because of reflectionsunlightAs we can see, the comet tail is facing away from the sun.The comet is huge, but its mass is pitifully smallBig cometIts mass is less than one ten thousandth of that of the earth.Since comet is composed of various frozen impurities and dustSolar time, it is just a small cloud like spot;When it is close to the sun, due to the evaporation, gasification, expansion and eruption of condensed solids, it produces a comet tail.The comet tail has a huge volume, which can reach hundreds of millions of kilometers.It has different shapes, some of which are more than one. It generally extends away from the sun, and the closer it is to the sun's tail, the longer it will be.
comet
The number of comets in the universe is huge, but only about 1600 have been observed.The orbit of a comet is very different from that of a planet. It is an extremely flat ellipse, and some even have parabolic or hyperbolic orbits.Comets with elliptical orbits can return to the sun regularly, calledPeriodic comet；Comets with parabolic or hyperbolic orbits can only approach the sun once in their lifetime, but once they leave, they will never return. They are calledAperiodic cometThis kind of comet may not have been a member of the solar system, but just a passer-by from outside the solar system. They accidentally entered the solar system, and then returned to the vast depths of the universe without hesitation.Periodic comets can be divided into short period comets (the period around the sun is shorter than 200 years) and long period comets (the period around the sun is longer than 200 years).
comet
The orbits of more than 600 comets have been calculated.The orbit of a comet may be affected by the planets and change.When the comet is accelerated by the influence of the planet, its orbit will become flat, or even become a parabola or hyperbola, so that the comet will leave the solar system;When the comet deceleratesEccentricityWill become smaller so thatLong-period cometBecomesShort period comet, even changed from an aperiodic comet to a periodic comet and was "captured".
Comet tail production
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Comet tails are thought to be composed of gas and dust;Four combined effects blow it out of the comet:
one
The initial value obtained when the gas and associated dust evaporate from the comet nucleusmomentum。
The interaction of these effects makes each comet tail look different.Of course, the matter evaporates toCometAnd the tail of the comet consume the material of the comet nucleus.Sometimes it appears in an explosive way,Comet BiraThat's it;It broke into two when it passed the sun in 1846, and disappeared after that pass in 1852.
origin
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In addition to some periodic comets, new comets with open or closed orbits continue to visitInner solar system。The question of where the new comets come from begins with the formation of the solar system.
The origin of the solar system
The predecessor of the solar system is a large cloud composed of gas and dust. 4.6 billion years ago, this cloud may be affected bySupernova explosionThe compression of the shock wave began to slowly rotate and shrink into a disk, with the young sun at the center of the disk.The cloud particles on the disk collide with each other, and a considerable proportion of the material condenses into planets and their moons, while some of the remaining cloud material condenses into comets.
When the solar system was young, comets could be seen everywhere. These comets often collided with newly formed planets, which had a profound impact on the growth and evolution of young planets.A large amount of water on the earth may be the legacy of many comets that collided with the young earth, and this water, later, gave birth to all kinds of life on the earth.
In more than 4 billion years after the formation of the solar system, comets near the central region of the solar system, or with the sunplanetCollision with a satellite, or evaporation from solar radiation, has disappeared, and comets we see should come from the edge of the solar system.If it is assumed that the cometary matter remaining in the periphery of the solar system has remained unchanged for billions of years, the study of these comets will help to understand the original chemical composition and state of the solar system.
The origin of comets
comet
The origin of comets is an unsolved mystery.It has been proposed that there is a huge comet area outside the solar system, where there are about 100 billion comets, calledOort Cloud, due to otherfixed starDue to the influence of gravity, some comets enter the solar systemJupiterSome comets escaped from the solar system, while others were "captured" as short period comets;Others believe that comets were formed near Jupiter or other planets;Others believe that comets were formed in remote areas of the solar system;Some people even think comets are visitors from outside the solar system.Because periodic comets have been disintegrating, there must be some way to produce new comets to replace old ones.One possible way is to store billions of stars orbiting the sun in various possible directions at a radius of 105 astronomical units away from the sunComet cluster。This concept is supported by observations, which show that aperiodic comets approach the sun in a very long elliptical orbit in a random direction.
As time goes on, due to the slight gravity given by passing stars, the orbit of distant comets can be disturbed until the distance of its perihelion becomes less than a few astronomical units.When the comet subsequently enters the solar system, the gravitational attraction of the planets in the solar system can transform this aperiodic comet into a new periodic comet (it will exist for thousands of years before its collapse).On the other hand, these forces can throw it completely out of the comet cloud.If this statement is correct, the records of about 1000 comets over the past few centuries are only a small part of the samples of giant comet clouds, which have not yet been directly observed.This kind of comet cloud associated with individual stars may be all over ourGalaxyInside.So far, no method has been found to detect a large number of comets that may form a set with the sun, let alone those comet clouds that form a set with other stars.The total mass of the cometary cloud is not clear, not only the total number of comets is difficult to determine, but also the mass of a single comet.It is estimated that the mass of the cometary cloud is 10 ⁻¹³～10⁻³Between the masses of the earth.
Oort cloud theory (Oort cloud theory): In 1950, Dutch astronomer Jan Oort proposed that there were trillions of comets in the spherical shell zone between 30000 AU and one light year away from the sun. These comets were remnants of the formation of the solar system.Some comets left their original orbits occasionally due to the influence of "passing" stars or collisions with each other.Most off orbit comets never enter the range that can be detected by large telescopes.Only a few comets enter the inner solar system in various orbits.However, up to now, the Otter cloud theory is only a hypothesis, and there is no direct observational evidence.
Kuiper Belt: The Oort cloud theory can reasonably explain the origin of long-period comets and the relationship between these comets andEcliptic surfaceThe randomness of included angle.But the orbit of the short cycle cometSolar system planetsThe origin of short period comets cannot be reasonably explained by the Otter cloud theory.
In 1951, American astronomer Gerard Kuiper proposed that there is a Kuiper belt (or Keiper belt) between 30 and 100 AU away from the sun. There are many ice bodies circling the sun on the belt. The orbital plane of these ice bodies is similar to that of planets. Occasionally, some objects in the Kuiper belt are disturbed and pulled by the gravity of outer planets, and move in the direction of the sunNeptuneIt is further influenced by the gravity of Neptune and enters the inner solar system as a short period comet.
Astronomers David Jewitt and Jane Luu have been searching for objects in the Kuiper Belt with highly sensitive electronic cameras that can detect extremely dim objects since 1988.They found the first such object in 1992 (1992 QB1). The average distance between 1992 QB1 and the sun is 43AU, and the cycle of revolution is 291 years.Kuiper Belt ObjectsAlso known asExtraNeptune objects（List of Transneptunian Objects）。From 1992 to October 2002, more than 600 Kuiper Belt objects have been discovered in succession (see MPC's List of Transneptunian Objects for the latest list).At this stage, astronomers believe thatPluto、Charon andTriton , probably entering the inner solar systemKuiper Belt Objects, and the discovery of Guaowa（Quaoar）, its size is aboutPlutoHalf of.
nature
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The nature of the comet cannot be known precisely because it is hidden in the comet and cannot be observed directly, but we can guess some of its properties from the spectrum of the comet.In general, these spectral lines indicate the existence ofOH、NHandNH₂Group gas, which can easily be explained as the result of the decomposition of stable hydrogen compounds of the most common elements C, N and O, namely CH ₄, NH ∨ and H ₂ O. The frozen ice of these compounds may be the main component of the comet nucleus.Scientists believe that all kinds of ice andsilicateThe particles are scattered in the comet nucleus in a loose structure, some like dirty snowballs, with a density of about 0.1 g/cm3.When the ice is heated and evaporated, it leaves behind loose rock material, containing individual particles ranging in size from 10 ∨ cm to about 10 ∨ cm.When the earth passes through the orbit of a comet, we regard the observed particles as meteors.There is reason to believe that comets may be part of the matter in the nebula that gathered to form the sun and planets.Therefore, people would like to try to obtain a sample of comet material for analysis so as to know more about the origin of the solar system.This plan can be done theoretically, such as trying to make a rendezvous with periodic comets in space.Such plans are under study.
observation
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Apart from being far away from the sun, the long, bright and sparse tail of a comet gave people the impression that the comet was very close in the pastearth, even within our atmosphere.In 1577, Tycho 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 toSmall objects in the solar system。Whenever a comet approaches the sun, its brightness increases rapidly.The observation of comets far from the sun shows that they move along the highly elongated ellipse, and the sun is at the focus of the ellipse, which is consistent with Kepler's first law.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, Newton's friend and donorHarley(1656-1742) realized that it was cyclical in 1705.Its average cycle is 76.1 years.Historical records show that it has been observed every time it passes through the sun since 240 BC and possibly since 466 BC.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.This change occurs because the solid material (comet nucleus) that makes up the comet suddenly becomes hot enough to evaporate and is called cometGas cloudEncircle the comet nucleus.The ultraviolet light of the sun causes the gas to glow.The diameter of a comet is usually about 10km, but its tail is often very long, reaching 10km 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,normans intrusionbritainOn the eve of this yearHalley'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 Normans conquered 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).
According to the AFP report on January 7, 2023, a comet named C/2022 E3 will pass through the perihelion on February 12 and the perigee on February 1. If the observation conditions are good, it will be clearly visible to the naked eye.[7]
Observation method
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comet
The visual observation of comets is the main observation project of young amateurs. Its method is simple and easy to do, with little funding. Most amateur observers can carry out it, and it is also used by some professional observers.Although photographic observation has become more common, a large number of comet visual observation data have been retained in history, so the visual observation data can be linked with the previous ones, maintain the continuity of visual observation, and can intuitively reflect the state of the comet, which is of great significance to the study of comet evolution, and has been paid attention to by the international comet community.
Visual observation includes the brightness estimation of comets, the measurement of the size and intensity of comets, and the study and description of comet tails.
Brightness estimation of comets
comet
Comets need to measure light in three parts: nucleus, comet head and tail.Since the comet tail is thin, small in contrast and fibrous, it is very difficult to measure its light, so the comet tail light measurement is not a conventional observation item.Usually, the so-called comet photometry is to measure the comet head (i.e. the total magnitudeM1）And nucleus (i.e. nuclear magnitudeM2）The brightness of.The comet nucleus is often invisible, or the condensation degree of the central part of the comet head is very high, and the comet nucleus cannot be distinguished clearly, etc., so it is relatively difficult to measure the light of the comet nucleus.In addition, what we mean by comet photometry is not only to measure itluminosity, record the measurement time, closely monitor the comet brightness change, and record the sudden change time. All these data are very useful for the analysis of nuclear properties.Several methods for estimating comet brightness:
one
Bobronikov method(Method B) When using this method, the observer should first select several comparison stars of neighboring comets (some are brighter than the comet, and some are darker than the comet).Then follow the steps below: (A) Adjust the focal length of the telescope to make the star and comet have similar visual size (that is, the star is not on the focal plane of the telescope, and becomes the external image of focus, called defocus).(B) Adjust the focal length back and forth between a pair of brighter and brighterDark starComet stars are interpolated between (seeMorrisMethod).(C) Repeat the second step between several pairs of comparison stars.(D) Take the average value measured in the second and third steps and record it to 0.1 magnitude.
two
Sidgwick method(S method) This method can be used when the comet is too dark to solve the problem by defocusing.(A) Remember the "average" brightness of comets on the focal plane (need to practice frequently, this "average" brightness may not be the same for different observers).(B) Defocus a comparison star so that its apparent size is the same as that of the focused comet.(C) Compare the surface brightness of defocused stars with the average brightness of focused comets remembered.(D) Repeat the second and third steps until a matching comparison star is found, or a reasonable interpolation can be carried out for the comet.
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Morris method(M method) This method is mainly to compare the moderate defocusing comet diameter with a defocusing star.It is the combination of the two methods above.(A) Defocus the comet head to make it have approximately uniform surface brightness.(B) Remember the comet image obtained in the first step.(C) Compare the comet image size with the comparison stars outside the focal length. These comparison stars are more defocused than comets.(D) Compare the surface brightness of defocused stars and remembered comet images, and estimate comets, etc.(E) Repeat steps 1 to 4 until a comet brightness of approximately 0.1 magnitude can be estimated.
four
In additionBayer(Bayer) method, because it is difficult to use this methodSky backgroundThe brightness is very sensitive, and it is generally not used to estimate the brightness of comets.
When a cometVisual magnitudeThe following interpolation method can be used between two comparison stars.It is estimated that comet brightness is the same as brightnessStellar brightnessThe difference is expressed as 1/10 of the star equivalency of two comparison quantities.Multiply this difference by the difference of the comparison stars, add this product to the magnitude of the brighter star, and round it to get the visual magnitude of the comet.For example, the magnitudes of comparison stars A and B are 7.5 and 8.2 respectively, and their star equivalences are 8.2 - 7.5=0.7.If the brightness of the comet is between A and B, the difference is about 6 × 1/10, so the estimated comet number is 0.6 × 0.7+7.5=0.42+7.5=7.92, which is about 7.9.
When the above three methods are used to estimate cometary stars, reference should be made to the star map marked with a large number of constellations, such as the AAVSO star map (the special star map of the American Association of Variable Star Observers).The labeling limit of the star map is 9.5, which is suitable for the comparison of comet brightness.Those stars that are obviously red are not used as comparison stars.When using this star map, it should be noted that the magnitude value does not have decimal places, for example, 88 is 8.8.In addition, the magnitude value can be divided into two types: underlined and non underlined. The underlined indicates the photoelectric magnitude.For example, 33 indicates photoelectric star magnitude 3.3, which shall be stated in the record report.
In addition, stars in the SAO catalog or other electronic star maps with accurate brightness labels can also be used as the basis for estimating comet brightness.Careful observers can also estimate the "nuclear magnitude".A telescope with a diameter of 15cm or larger should have a higher magnification.During observation, the observer's vision should be very stable, and the nucleus should still remain star shaped under high magnification.Compare the comet nucleus with the comparison star at the focus, and the comparison star map still uses the above star map.Using several comparison stars, the estimated magnitude accuracy can reach 0.1.The nuclear magnitude of comets has certain reference value for studying the rotation and size of comet nuclei.
Comet and life
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Comet is a special kind of star, which may have an important connection with the origin of life.Comets contain many gases and volatile components.According to spectral analysis, mainlyC₂、CNC ∨, andOH、NH、NH₂、CH、Na、C、OIsoatoms and atomic clusters.This means that comets are rich inOrganic molecule。Many scientists have noticed this phenomenon: perhaps life originated from comets!In 1990,NASAKevinJ. Zahule and Daid GridspoonCretaceous－TertiaryThe organic dust in the stratum near the boundary is interpreted as follows:amino acidThis kind of organic dust is formed;It is pointed out that in the early stage of the formation of the earth, comets could alsoOrganic matterIt rained on the earth like a light rain - this is the source of life on earth.
Naming rules
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Before 1995, comets were listed in small letters in English according to the order of discovery each year.For example, the first comet discovered in 1994 was 1994a, and so on. After a period of observation, the orbit of the comet was determined and corrected, the order of passing the perihelion of the comet was followed by the Roman numerals I, II, etc. (this number is usually compiled two years after the end of the year).asComet Shoemaker Levy 9Are numbered 1993e and 1994 X.
In addition to the number, comets are usually named after their discoverers.A comet can only bear the names of three discoverers at most,Comet Shoemaker Levy 9Its English name is Shoemaker － Levy 9.
Since 1995,International Astronomical UnionReferring to the naming rule of asteroids, the new comet numbering method is adopted in English alphabetical order with half a month as the unit.If I and Z are removed from all English letters, the order of the remaining 24 letters is unnecessary. For example, the first half of January is A, the second half of January is B, and so on, the second half of December is Y.
comet
Later, the comets discovered in the same month and a half were numbered 1, 2, 3, etc.In addition, in order to facilitate the identification of the comet's status, a mark is added before the number:
A/Possible asteroid
P/For short period comets that have returned more than once, add the serial number of periodic comet list before P (for example, Halley's comet 1P/1982 U1 or 1P for short)
C/long-period comet (with a period of more than 200 years, such asComet Hale BoppC/1995 O1)
D/Comet that no longer returns or may have disappeared (e.g. Comet Shoemaker Levy 9 is D/1993 F2)
Annex S/Newly discovered Planet Satellites
If the comet breaks up and splits into more than nuclei, add - A, - B... after the number to distinguish each nucleus.In terms of regression comet, if the comet is observed again, an IAU shall be added before P/(or possibly D/)Asteroid centerThe given serial number to avoid re marking when the comet returns.For example, Halley's Comet has the following marks: 1P/1682 Q1=1P/1910 A2=1P/1982 U1=1P/Halley=Halley's Comet.
On October 8, 2021, the International Asteroid Center (MPC) released a new comet, named C/2021S4 (Tsuchinshan), discovered by the Near Earth Object Telescope of Xuyi Observatory of Zijinshan Observatory.This is the seventh comet discovered by the Zijinshan Observatory, and also the fifth comet named after Tsuchinshan.[6]
On March 1, 2023, the International Asteroid Center released a new comet C/2023 A3 (Tsuchinshan ATLAS) observed by the NEO telescope.This is also the eighth comet discovered by the Zijinshan Observatory of the Chinese Academy of Sciences.[9]
Meteorite meteor relationship
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Meteors and comets are not necessarily linked, but most of them are produced by comet trails.meteoryesInterplanetary spaceDust particles and solid blocks（Meteoroid）The light trace generated by the friction and combustion between the earth's atmosphere and the atmosphere.If they are not burned out in the atmosphere, they are called "meteorites" or "meteorites" after falling to the ground.Meteoroids originally surroundedSolar motionWhen passing near the earth, the earth's gravity will change its orbit and enter the earth's atmosphere.Many meteors come from a point in the sky（Radiant point）It radiates outward, which ismeteor shower。
Encyclopedia x Knowledgeable: Illustrated Meteor Shower
The earth will often encounter foreign small bodies.These small bodies will rub and burn violently with the earth's atmosphere after entering the earth's atmosphere.This is a meteor.If the meteor falls to the ground before it has burned out, that isMeteorite。Meteorites can be divided into stone meteorites, iron meteorites and stone iron meteorites according to their main chemical composition.Meteorites bring us rich information about the formation and evolution of solar system celestial bodies, and they are welcome guests.Every day, billions or tens of billions of meteoroids enter the earth's atmosphere, with a total mass of 20 tons.Their radii and masses differ greatly from each other and cannot be generalized.If the diameter of the small object hitting the earth is more than 10 kilometers, the damage will be the same as that caused by the extinction of dinosaurs.
Before giving a permanent number to a periodic comet, the comet needs to pass through the perihelion again after being found, or get the proof that it has passed before it can be numbered.E.g. No. "153P"Chi Gu, Comet ZhangIts revolution period is more than 360 years. It was proved that the comet appeared in 1661 was the same, so it was numbered.Please refer to the website for other periodic comets without numbers.
Comets are usually named after their discoverers, but a few are named after themTrack calculationFor example, Halley's Comet numbered "1P" and "2P"Comet EnkeAnd "27P" Comet Karen Merlin.At the same time, the orbit and revolution period of comets will be changed due to the influence of Jupiter and other large celestial bodies. They also disappear for some reason and can no longer be found, including disintegration in the air, planetary gravity, and depletion of matter through the comet tail.
No./name Chinese name Discoverer/rediscovery period (year)
0.0 0.230+5.5 The perigee of 1996 Comet Baiwu is only 0.1AU
Comet love joy
21p
The perihelion of the comet with the largest absolute brightness in history is as far as 4.1AU, so it is not bright
Earth "Water Delivery Worker"
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A "comet storm" around Corvus
When the Earth was formed about 4.5 billion years ago, the heat of the sun drove most of the water in the solar system to the periphery of the galaxy. The water still exists in the form of ice in Saturn's ring, Jupiter's satellite Europa, Neptune, Uranus and billions of comets.But there is also enough water on the earth. Scientists have always wondered how the water came from[5]。
At present, there is a mainstream theory that this water was brought by a series of comets roaring into the sun about 500 million years after the formation of the Earth.Last week, scientists found that at least some comets have substances with the same chemical properties as water on the earth, making significant progress in the study of this theory.
Shortly after this research progress was announced, American astronomers found another important evidence to support the above theory.This evidence comes from a bright star that can be observed in the northern hemisphere -CorvusEta Corvi, a star about 400 trillion miles away from Earth.Kerry Lees, the chief researcher of Johns Hopkins University in the United States, said: "We observed a primitive comet 'storm' there, which hit a star closer to it violently."
What Liss and his colleagues observed was actually the infrared characteristics of some cosmic dust, which was about three astronomical units away from Corvus, that is, three distances from the Earth to the sun.Detailed observations by the Spitzer Infrared Space Telescope show that they were produced by the strong impact of giant rocky stars.Liss said: "We have observed nano diamonds and amorphous silicon, which indicates that the smallest volume of the object colliding with the comet is equivalent to the asteroid Ceres, and the largest is several times of the Earth."
This observation is not enough to conclude that cosmic dust is produced by impact.Liss admitted that in addition to the "storm" composed of small comets, he also observed the remnants of a large star."As a result, we are not sure, we only know that a large number of substances are ejected around." Liss and his colleagues can not observe all the substances. What they observed is a special substance that only contains ice particles and organic compounds, and these substances only exist in smashed comets.
In addition, the chemical characteristics of these remote dust are very consistent with the Almahata Sitta meteorite that fell into Sudan in 2008.The meteorite is likely to come from the Kuiper Belt outside Neptune, where billions of comets, Pluto andEris Dwarf planets are also distributed in that area. In fact, they are giant comets themselves.
Collect all the discoveries, and you will get a picture depicting how water, even the basic material for forming life, appeared on the earth one billion years after the birth of the solar system.Since the Corvus galaxy has been formed for 1 billion years, it naturally raises the question: Is it possible for life to exist there?At first, you may not recognize the evidence that it is conducive to the formation of comet "storm".However, the current answer is: No."We have studied about 1000 galaxies, and only the constellation Corvus meets this condition." But he also stressed that this does not mean that there is no such evidence in other regions.If the James Weber Space Telescope can be put into use as early as 2018 with the approval of the US Congress, this more sensitive telescope can find more promising clues.In other words, it is too early to draw the conclusion that "life on earth originated from a cosmic accident".
