Vesta,Asteroid serial numberby4 Vesta, Yessolar systemmaximalasteroidOne, averagediameter525 km (326 miles).It isHeinrich ObersIt was discovered on March 29, 1807, named after Vesta, the goddess of home and fireplace in Roman mythology, and translated into Chinese as Vesta.
Vesta is the successordwarf planetCeresAfter that, the highest massMain Belt Asteroids , possessionMain Asteroid Belt 9% of the total mass.Although the mass ratioZhishen StarA little more, but smaller, is the second largest asteroid.Vesta forms the remnant of rocky planetProtoplanet（Internal differentiation）。1、 Two hundred million years ago, Vesta was impacted, producing many fragments, leaving two huge impact craters, and the southern hemisphere has a high density.Some fragments of this event have fallen to the earth and becomeHED meteorite, providing a rich source of information about Vesta.
Vesta is visible from the earthThe brightest asteroidThe farthest distance from the sun is only a little farther than the nearest distance from Ceres, but Vesta's orbit is completely within the orbit of Ceres.
NASA'sDawn spacecraftFrom July 16, 2011 to September 5, 2012, he entered the orbit around Vesta, made nearly a year of exploration, and then went to Ceres.Researchers continue to analyze the information collected by Dawn, hoping to better understand the formation and history of Vesta.
Discovery history
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Vesta was discovered by German astronomer Heinrich Wilhelm Olbers on March 29, 1807.He accepted the advice of Gauss, an outstanding mathematicianRoman mythIt is named after Vesta, the goddess of the family and fireplace.
After the discovery of Vesta in 1807, no other asteroids were found for 37 years.During this period, only four asteroids were known, so they had their own symbols (symbols). The Vesta logo had the style of fireplace.
Vesta, the goddess of family and fireplace
vesta and ceres
Vesta andCeresBetween Mars and JupiterAsteroid beltVesta is the second largest asteroid, after Ceres.And is 2.5 astronomical unitsKirkwood gapInside Largestasteroid。Its volume andZhishen StarSimilar (within the error range), but larger.The shape of Vesta seems to have been affected by gravity. It is an oblate sphere, but the large depression and prominence make itInternational Astronomical UnionThe 26th Congress was categorically excluded from the planet.Therefore, Vesta will continue to be classified as an asteroid, still a small body in the solar system.For the asteroid, its rotation (5.342 hours) is relatively fast, and its direction is in the direct direction,North PolePointing to the right ascension of 20h32m, the right latitude of+48 °, the error (uncertainty) is about 10 °, and the tilt angle of the rotation axis is 29 °.The surface temperature is estimated to be - 20 ℃ at the middle of the day;In winter, the temperature at the pole is as low as - 190 ℃, and the normal daytime and nighttime temperatures are - 60 ℃ and - 130 ℃ respectively.The above estimate was completed on May 6, 1996, when Vesta was very close to the perihelion, and the details would change slightly with the seasons.
Geological characteristics
For Vesta, scientists have a large number of powerful samples to study, more than 200HED meteoriteIt can be used to gain insight into the geological history and structure of Vesta.Vesta is believed to have a metal core mainly composed of iron and nickel, which is covered witholivineDominantmantleAnd rock crust.It is the earliest calcium and aluminum rich material (the earliest solidified material in the solar system about 4.567 billion years ago). The possible time sequence is as follows:
Vesta
It will be completed accumulatively in about 2-3 million years.becauseRadioactive decayAfter 4-5 million years, all or most of aluminum 26 gradually separated and settled to the core.
mantleOfConvection, resulting in melting and further crystallization. After about 6-7 million years, when 80% of the material crystallizes, the convection stops.The remaining molten material is formed by eruption or by eruption of lavabasalt, or the ocean that forms magma for a short time, forming the crust.The deeper crust is formed by crystallizationigneous rock, older basalt becomesMetamorphic rock。
Slow cooling inside.
Vesta is an intact, renewed surface and an asteroid that has experienced planetary differentiation.However, the existingIron meteoriteandAchondriteFailed to be confirmed on the parent.In the classification of meteoritesStar ChildIn the process of purgatory historyto hitDebris generated.Vesta's crust is considered to have the following hierarchy (in order of depth):
The petrified weathering layer is derived from the eruption of ancient cupro calcic granite and breccia.
Vesta
The lava flow of basalt comes from non thrustEruption。includepyroxene, variable pyroxene, plagioclase and other igneous rocks, from the eruption of thrusting.
The orthopyroxene igneous rock with large grains is from the ancient copper meteorite.
According to the size of the V-type asteroid (Vesta shell fragments thrown out during the big impact) and the depth of the Antarctic crater, the thickness of the shell is estimated to be about 10 kilometers.
Surface characteristics
Vesta
The most obvious feature is that there is a hugevolcanoThe width of the crater reaches 80% of the diameter of Vesta, the depth of the bottom of the crater reaches 13 kilometers, the outer edge is 4 to 12 kilometers higher than the surrounding terrain, the total height difference reaches 25 kilometers, and there is an 18 kilometer high mountain in the center.It is estimated that this impact will throw out about 1% of the volume of Vesta, and the V-type asteroid of Vesta family is produced by this impact.Except thisMeteorite craterIn addition, several relatively large craters (about 150km in diameter and about 7km in depth) have also been observed.One is 200 kilometers widereflectivityThe dark region has been named Obos to honor the discoverer of Vesta.However, Obos is not shown in the contour map, so it is a newly generated pit, or an ancient onebasaltOn the surface, it is unknown.It is selected as the reference point of longitude 0 °, and the prime meridian on the definition passes through its center.
Eastern Hemisphere andwestern hemisphereThe terrain is obviously differentHubble Space TelescopePreliminary spectral analysis of the image shows that there are several kinds of highreflexThe area with high frequency, heavy pit terrain accompanied by aged weathering layer, and the depth is enough to detect the pit of igneous rock stratum.On the other hand, large areas of the Western Hemisphere are believed to be basaltdarkThe surface occupied by geological organization may be similar toMoon Sea。
basin
The basin on Vesta is considered to be a huge impact crater, named after the Virgo Vesta.
The impact craters on Vesta are mostly named after the Virgo of Vesta. Marcia, Calpurnia and Minucia were once nicknamed as snowman impact craters because they were connected to each other and arranged in order from bottom to top.
name
coordinate
Diameter (km)
Name Source
Talpia impact crater
69.5°S 29°E
forty-one
Talpia，the Vestal Virgins one of;At the same time, she was also the daughter of the Roman governor, who betrayed Rome and led the enemy into the city.
SomeHED meteoriteIt may come from the deep part of Vesta, which can provide clues to the internal structure and geological history of Vesta.The infrared study of asteroid 1999TA10, 237442, suggests that it came from the interior of Vesta.Combined with the detection data of Dawn spacecraft, the internal structure of Vesta can be calculated (figure).It has an iron nickel core with a diameter of 214 ～ 226 km, accounting for 18% of the total mass. Outside it are the mantle of peridotite and the outermost crust.onlyterrestrial planetSuch core, mantle and crust structures only exist in large satellites.
The composition of Vesta shell increases in depth as follows:
Lithified topsoil, which is ancient copper and calciumAchondriteAnd brecciated anortholite;Basaltic lava flow is a source of non accumulated calcium feldspar gabbro achondrite;The plutonic rock composed of pyroxene, variable pyroxene and plagioclase is the source of the cumulated anorthoclase;enrichmentOrthopyroxeneLarge grained plutonic rocks are the source of the trondhjemite.Based on the size of the V-shaped asteroid that threw debris from the Vesta crust during the great meteorite strike and the depth of the Ryersilvia crater, the thickness of the Vesta crust is estimated to be about 10km.
The geosyncline of Vesta must be the descending terrain caused by fracture, which indicates that Vesta has more complex geology than other asteroids.If Vesta remained spherical, it would surely be classified as a dwarf planet.It was not officially regarded as a dwarf planet because of the deformation of its Antarctic region caused by the big impact.The impact caused the change of Vesta rotation speed and the earth trough dwarfed the 465km long, 22km wide and 5km deep Grand Canyon.
According to the analysis and research of meteorites, the calcium aluminum rich inclusions (CAIs) of carbonaceous meteorites, the earliest solid matter in the solar system, were formed 4.567 billion years ago, and are generally regarded asSolar system planetsThe time benchmark at which the process of volume accretion formation begins.From this, the time line of Vesta's formation and evolution history is as follows: Vesta has completed accretion in 2-3 million years;From 4 million to 5 million years, the radioactive decay energy of 26Al caused complete or almost complete melting, resulting in the separation of metal nuclei;6~7 million years, the convection melting mantle continuously crystallizes, and when about 80% of the material crystallizes, the convection stops;The remaining molten material may be used as a continuous eruption of basalt flow, or may become a short-lived magma sea, condensed into crust;The deeper crystallization of the crust forms the plutonic rock, and the older basalt is metamorphic due to the pressure of the newer surface layer;The interior cools slowly.
Based on relevant observational evidence and theoretical researchSolar system planetsThe "standard" model (figure) formed is summarized as follows:Solar nebulaThe self attraction shrinks to form the central "Protosun" and the nebula disk rotating around it;The solid particles in the nebula disk are the basic building materials for forming planets. The particles first gather into small planetesimals, which collide and combine to grow into large planetesimals. The large planetesimals' gravitational field is strong enough to accrete the particles and small planetesimals they encounter, which soon become protoplanets or planetesimals, and they collide with each other and further accrete to grow into planets;In the inner region of the nebula disk near the sun, the temperature is high, and only the condensed particles of dust matter form the rock massterrestrial planet；In the outer region of the nebula disk, the temperature is low, and water and other ice substances are involved in the condensed particles, so that large planetary tires can be formed more quickly, and gas can be accumulated to becomeJupiter like planet；Asteroids are semi-finished products in the process of planet formation. Due to the gravitational perturbation between large planetesimals in the outer region of the nebula disk, some planetesimals' orbits change and pass through the asteroid region, where the construction materials, including small planetesimals, are absorbed and taken away, making the growth of protoplanets stop in the semi-finished state.Vesta is the known original planet that only renews its surface in the above evolution way.However, the parent iron meteorite andAchondriteThe existence of indicates that there once existed other differentiated star particles with igneous history, which were later smashed by impact.Vesta and its fragments——HED meteoriteThe exploration research has obtained a lot of valuable new information that was not well understood in the past, which is helpful to solve the problem of the origin and early evolution of planets such as the Earth.
A thorough study of the Vesta exploration data obtained and the Ceres exploration data to be obtained will lead to a new breakthrough in the study of the formation and evolution of planets.
Detection activities
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Acquired by NASA Dawn probe
NASA'sAurora Project It will be the first plan to explore Vesta, and is expected to enter orbit for 9 months from 2010 to 2011.
On September 27, 2007,US Eastern TimeAt 7:34 (19:34 Beijing time), the "Dawn" was launched fromFloridaCape Canaveral Air BaseCarried by a Delta 2 rocket, it successfully lifted off, starting its eight year long interstellar exploration journey of more than 5 billion kilometers.It will go far between Mars and JupiterAsteroid belt, first explore Vesta, and then go to Ceres to continueobservationTo help experts find clues to the birth of the solar system.
According to the plan, it will fly to the orbit around Vesta in 2011, and continue to travel after the 6-month observationCeres, expected to reach Ceres in 2015.If you live up to your mission“dawn”Will become the first to orbit two different celestial bodiesUnmanned detector。
According to August 2006International Astronomical UnionCeres has been upgraded from asteroid todwarf planetHowever, NASA has not changed its tune and still calls "Dawn" an asteroid probe.
Scientists believe that the detection of Vesta and Ceres will help to understand the origin of the solar system, hence the name of the project "Dawn".
On May 3, 2011, Dawn took the first picture when it was 1.21 million kilometers away from Vesta, which is only about 5 pixels wide.Dawn entered the exploration phase of approaching Vesta, and began to decelerate on June 12, preparing to enter the orbit around Vesta in 34 days.
On June 1, 2011, when Dawn was 483000 kilometers away from Vesta, 20 consecutive photos were taken for navigation, with a resolution close to that of Vesta taken by the Hubble Space Observatory.Dawn will slow down before reaching Vesta and is expected to release more photos every week.Dawn is expected to enter orbit around Vesta on July 16, 2011.
NASA confirmed that Dawn entered the orbit around Vesta on July 16, 2011, becoming the first probe to orbit an asteroid in the asteroid belt.The exact orbital time of Dawn is not clear, because astronomers could only estimate the mass and gravity field of Vesta at that time, and could not accurately know its data.When Dawn is in orbit, it can calculate the mass and gravity field of Vesta in turn.At 06:30 UTC on July 17, Dawn retested the equipment and instruments on board.
Dawn entered an orbit 680 kilometers away from Vesta on September 27, and spent 12.3 hours circling it.Dawn later entered another orbit on December 8, only 210 kilometers away from Vesta, and took 4.3 hours to orbit.NASA first released the preliminary data of Vesta obtained by Dawn in May 2012. It is estimated that the diameter of the metal core of Vesta is 220km.NASA scientists further regard Vesta as a special asteroid, and believe that it is a remnant of a large asteroid formed at the same time as a rocky planet.
On September 7, 2012, Dawn was launchedUS Eastern TimeAt 2:26 a.m. on the 5th, he left the orbit of Vesta and flew to Ceres.If all goes well, Dawn is expected to become the first unmanned probe to orbit two different celestial bodies.
