Michael E. BrownOn his website, he said, "The new object we found is the farthest and coldest one in the solar system, so we think it is suitable to be named after the sea goddess Sedna in the myth of Inuit, who is said to live in the depths of the Arctic Sea."[3]。Brown also suggested that the International Astronomical Union Asteroid Center should use all the objects found in the Sadna revolution area in the futureArcticGod of.This object is officiallyOfficial namePreviously known as Sedna[4], its temporary name was 2003 VB12.Asteroid centerdirectorBrian Marsden Some people think that this behavior violates the naming protocolInternational Astronomical UnionMembers of may also vote against[5]。However, no astronomer objected to the name later, and no other name was proposed, so the International Astronomical Union officially accepted the name Sedna in September 2004.The International Astronomical Union also believes that in the future, if similar circumstances are encountered, astronomers may be allowed to publish the names of celestial bodies before the official names are determined.[4]
SpainWith the rest of the United States（Arizona）OfobservatoryThe object was also observed within a few days.AmericanSpitzer Space Telescope This area was also being observed at that time, but it was not found.Astronomers later used the Spitzer Space Telescope to observe Sedna, and calculated that the upper limit of its diameter was aboutPlutoThree fourths of (less than 1600 km).[6]
Comparison between the orbit of Sedna and other celestial bodies in the solar system Sedna has a very elliptical orbit, and its perihelion and aphelion are estimated to be about 76 AU and 937 AU respectively, which is the farthest perihelion from the sun among the celestial bodies observed by astronomers[7]。Sedna was approaching the perihelion when astronomers found it. At that time, it was 89.6 astronomical units away from the sun, which was the farthest from the sun observed by human beingscelestial bodies 。Eris Later, it was found by astronomers at a distance of 97 astronomical units from the sun, which is farther than the location where Saidina was found.Some long-period comets will travel farther than Serena, but they are too dark to be observed (unless they are near perihelion).Even if Sadna reached the perihelion in 2076, the sun is still only a very bright star in the sky, only 100 times brighter than the full moon, and it is too far away to useVisual observationTo the disc face.[8]
Sedna'sRevolution periodAbout 11400 years[7]，It will pass through the perihelion between the end of 2075 and the middle of 2076, and Sedna will also overtake Eris in 2114, becoming the spherical object furthest from the sun in the solar system.[9]
According to the research of Harold F. Levison and Alessandro Morbidelli, astronomers at Observatoire de la C ô te d'Azur, France, the formation of Sedna orbit may be caused by afixed starIt is caused by passing near the celestial body at a close distance (less than 800 astronomical units) within 100 million years after the formation of the solar system, or by a star formed at the same time with the sun separating from the solar system later[10]。They also put forward another explanation: Saidena may be located in aBrown dwarfIt was formed nearby and later captured by the sun when the brown dwarf passed through the solar system.Although the probability of this happening is lower, it may explain the formation of Sedna more accurately.(For details, see“Nemesis”, speculated possible solar companion)
Astronomer Gomez put forward another explanation, saying that Sedna was affected by aOort CloudOf unknown planets.Recent simulations have shown that Sedna may be disturbed by an object located at 2000 AU or closer (with a mass equivalent to Neptune), or a star withJupiterAn object with a mass of 5000 astronomical units, or even a similar mass at 1000 astronomical unitsearthThe influence of celestial bodies.[11]
Asteroid 148209It is another celestial body with a Sedner like orbit, although it has no such extreme orbit: its perihelion is 44.3 AU, and its aphelion is 394 AU,Orbital periodIt was 3240 years ago.Its orbit may be similarly affected as that of Sedna.
When astronomers first found Sedna, they thought thatRotation periodQuite long, between 20 and 50 days[8]。Astronomers infer that such a long rotation period is a large satellitegravitationCaused by pulling, such asCharonA type of satellite, so astronomers try to find its satellite.But according toHubble Space TelescopeAccording to the observation results made in March 2004, astronomers did not find a satellite orbiting itrevolution。andMulti mirror telescopeSubsequent observations showed that the rotation period of Sedna was about 10 hours, which was consistent with the size of Sedna.[12]
Physical characteristics
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The imaginary Sedner horizon can see the Milky Way, the Sun, Antares II and Kota I
Sedna'sApparent magnitude1.8, etc,AlbedoIt is estimated to be 0.32, so it is inferred that the diameter of Sedna is about 1000 km[13]。When it was discovered by astronomers in 2003, it was discovered by humans since 1930PlutoThe brightest celestial body ever found in the solar system.Sadna'sDiscovererIn 2004, the upper limit of its diameter was considered to be 1800km[14]However, astronomers used the Spitzer Space Telescope to observe Sedner in 2007, and believed that its upper diameter was below 1600 km.Herschel Space Observatory The observation results in 2012 showed that the diameter of Sedna is 995 ± 80 km, which is more thanCharon It's smaller.Because Sedna has no satellite, astronomers cannot estimate its mass unless it is launchedspacecraftTo detect it at close range[15]。Suppose its density is equal to that of Pluto, 2.0gram/Cubic centimeter, then the mass of Sedna is about 1 × 10 ² ¹ kg.
Observations from the Toloro Mountain Intercontinental Observatory show that Sedna is one of the reddest objects in the solar system, and its color is similar to Mars.GeminiChad Trujillo And his colleagues think that the dark red color of Saidena is due to hydrocarbonprecipitateOr simpleOrganic compoundLong term exposure toultraviolet raysFormed underTorinThe result of covering the surface is like that of an asteroidForas Same as found on.The substance and spectrum on the surface of Sedna are quite uniform, which may be because it is too far away from the sun and is rarely affected by other celestial bodies, so it does not expose its internal structure like the dragon star.Sedna and two very distant celestial bodies（Asteroid 87269And asteroid 308933)Asteroid 5145The colors are similar, just like the classic outsideKuiper beltCelestial objects are the same, indicating that they all have the same origin[16]。Seidra superficialMethane iceorWater iceVery few, unlike Pluto or Pluto.
Trujillo and his colleagues think that the surface of Sedna is 60%methaneIce and 70% water ice[17]。Methane ice receivesRadiation exposureAfter,TorinCan be formed on the surface of Sedna[18]。Baruch and his colleagues are comparing Sedna withtitanLater, it was found that the object had weak methane and nitrogenSpectral line。According to these observations, they believe that the surface of Sedna consists of 24% Torin (similar to Titan), 7%Amorphous carbon、26%methanolIce and 33% methane[19]。Spitzer Space Telescope infraredPhotometric measurementIn 2006, it was confirmed that there were methane and water ice on the surface of Saidina.Astronomers believe that its surface may havenitrogenExists, so it may haveatmosphere。Seidra superficialmaximum temperatureIn 200 years close to the sun, it will exceed 35.6K (- 237.6 ℃), which can transform the solid nitrogen or phase into the beta phase, similar to Titan.Nitrogen at 35KVapor pressure14 microbar[19]。But Sadna's deep redSpectral slopedisplayOrganic chemistryHighly concentrated on the surface, weak methane spectral lines indicate that the methane on its surface is not newly generated.Astronomers infer that the surface of Sedna is too cold, so the methane cannot evaporate, and then falls on the surface like snow (similar to Titan, Pluto may also have this situation).Astronomers viaRadioactive processThe generated internal heating phenomenon is believed to haveLiquid waterConstituted ocean[20]。Amateur astronomerYou can use advanced computer software and long exposure photography to search for Sedna.
ethnic groups
Unless this discovery is just a fluke, astronomers are likely to detect other objects with highly elliptical orbits such as Sedna. Astronomers estimate that there are 40 to 120 such objects in the region where Sedna operates.The orbit of the asteroid 148209 is similar to that of Sedna. The perihelion is 44.3 AU, the aphelion is 394 AU, and the orbital period is 3240 years. Its formation process may be the same as that of Sedna.
Astronomers have proposed that every mechanism for explaining the Sedna elliptical orbit clearly shows such celestial structure and mechanical model.If there are objects outside Neptune, all similar objects will have equivalent perihelion (about 80 astronomical units).If Sedna is captured from a star system with the same rotation direction as the sun, such objects will have lowInclination angle，Semimajor axis100 to 500 AU.If it is captured from another star system whose rotation direction is opposite to the sun, it will form two groups, one with low inclination angle and the other with high inclination angle.The gravity of the star will cause the perihelion and tilt angle of the celestial body to disperse, and the angles and quantities are different.[21]
The large amount of data obtained by astronomers from such objects can determine which situation is more likely to occur.Brown said in 2006, "I call Sedna earlysunlightThe fossil record of the series.Finally, when other fossil records are found, Sedner will help us understand how the sun formed and how many stars were close to the sun when it formed.Brown made an observation between 2007 and 2008, trying to find other members of such objects as Sedna.This observation extended the scope to 1000 astronomical units and found thatOuter Sea UranusAsteroid 225088However, no objects similar to Sedna have been observed.Subsequent new computer simulation data show that about 40 objects similar to Sedna may appear in this area.[22]
classification
Asteroid centerRegard Sedner as aEcliptic discrete objectsHowever, this classification has many problems.Many astronomers believe that Sedna is associated with a few other celestial bodies (such asAsteroid 148209）It should be classified as a new type of celestial body, called extended ecliptic discrete objects (E-SDO), separated objects, remote separated objects (DDO) orDiscrete extended ecliptic objects (according to the official classification of the ecliptic sky survey plan)[32]。
The discovery of Sedner also made astronomers face a new problem: "What kind of celestial body can be regarded as a planet".A mass media article on March 15, 2004 reported the news of Sedna as follows: "The 10th planet has been discovered".laterInternational Astronomical UnionResolution adopted on August 24, 2006Planetary definitionTo solve this problem, it is believed that the planets must clear the nearby small bodies.Astronomers estimate that the Stowe Livingson parameter of Sedna is between 8 × 10 ⁻ and 6 × 10 ⁻ of Pluto. Therefore, even if no other objects have been found around Sedna, it is impossible to believe that Sedna can clean up nearby small objects.Astronomers wonder whether Seidra has reachedHydrostatic balance(Hydrostatic equilibrium), but it is still uncertain[33]。If it really reaches hydrostatic equilibrium, it will be regarded asdwarf planetIs a candidate object.
origin
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Sedna photographed by Hubble Space Observatory
In his paper announcing the discovery of Sedna, astronomer Brown regarded Sedna as the first human observationOort CloudCelestial bodies.Oort cloud is surroundedsolar systemSphere ofcloud cluster, full of comets, about one light year away from the sun.Sedna'sPerihelion76Astronomical unit, so unlikeEcliptic discrete objectsIts orbit will be affected by Neptune's gravity.Because it is more than other assumptionsOort Cloud ObjectAnd close to the sun,Rail inclinationWith planets andKuiper beltIt is approximately in a straight line, so they regard Sedna as the "Inner Oort Cloud Celestial Body", located in the area between the Kuiper Belt and Oort Cloud.
If the sedna was formed in the region, the sun'sProtoplanetary disk An area extending to at least 75 AU[23]。The original orbit of Seidra must be circular, unless it is formed by accretion of other small objects, but becauseProtoplanetBetweenrelative velocityQuite inconsistent, so this is not a big casePossible。Sadna must be attracted by other celestial bodiesInteraction[24], and then enterElliptical orbit。In the earliest paper, Brown, Rabinowitz and their colleagues had three possibilities:Not foundA planet located outside the Kuiper Belt, a star passing near the sun, or a young star fused with the sun when it formed.
Michael Brown and his team's preferred hypothesis is that aThe stars of the cluster put Sadna into an elliptical orbit.They think itsApohelionAbout 1000 AU, more than othersLong-period cometSo a star passing near the sun cannot affect its orbit.Brown thinks the best explanation is that the sun formedOpen clusterSeveral other stars were also generated, which later separated and affected the orbit of Sadna[25]。Alessandro Morbidelli and Scott J. Kenyon later revised this hypothesis[26]。Jolo Fernandez and Adrian Brunini believed that some young stars in the open cluster would approach the sun closely for many times, which would result in many objects with orbits similar to that of Sadna.According to a study conducted by the astronomers Mobidri and Harold F. Levison of the Observatoire de la C ô te d'Azur in France, the orbit of Sedna is most likely caused by a star passing through Sedna at a distance of less than 800 astronomical units in 100 million years after the formation of the solar system.
Many astronomers (including Gomez and Patrick Lekavica) describe it through several different modelsExtraNeptune objectsHypothesis.One hypothesis is that Sedna's orbit is disturbed by an unknown planet in the Naolt cloud.Recent computer simulations have shown that Sadna may be disturbed by an object located at 2000 astronomical units (or closer) (with a mass equivalent to Neptune), orJupiterAn object with a mass of 5000 astronomical units, or even an object with a mass similar to that of the Earth at 1000 astronomical units[27]。Patrick Lekavica's computer simulation believed that the orbit of Sedna was caused by an object similar to the Earth. Neptune ejected it in the early stage of the formation of the solar system, so it revolved around a narrow orbit of 80 to 170 astronomical units[28]。Michael Brown's sky survey plan did not find any Earth like objects within 100 astronomical units, but such objects may be thrown out of the solar system after the formation of the Inner Oort Cloud.
Another hypothesis is that Sedner's orbit is a huge and distant one (tens of thousands of astronomical units away)Solar companionCaused by,NemesisIs one of the possible solar companion stars.Nemesis is a dark star that is speculated to exist and may be periodicMass extinction、MoonImpact eventAnd the main cause of the orbital rotation of many long-period comets[29]。But there is no Nemesisdirect evidence, many evidences (e.gImpingement pit count）All question its existence[30]。John J. Matese and Daniel P. WhitmireLong term supportScholars of the existence of distant solar companion stars believe that a celestial body located at 7850 astronomical units and with a mass five times that of Jupiter can lead to the celestial body having a revolution orbit similar to that of Sedna[31]。Mobidri and Kenyon also put forward another view: Sedner may be in anotherStellar system(especially those whose mass is 20 times smaller than that of the sunBrown dwarf）Formed nearby, it was captured by the sun when it passed near the solar system.
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Sedner will pass through the perihelion between 2075 and 2076. It will be the best time for humans to detect this object when it is close to the sun, because the next time it passes through the perihelion will be 12000 years later.althoughNASASerena was listed on the Solar System Exploration website, but no exploration plan was considered.
