Ceres is the smallest and only planet in the solar systemAsteroid beltOfdwarf planet。By Italian astronomersPiazzi It was discovered and published on January 1, 1801.
Ceres is probably a differentiation planet with a rock core and a large amount of ice water in the mantle layermaterialA large number of water carrying minerals have been detected on the surface of the planet.It is preliminarily estimated that water accounts for 40% of the volume of Ceres.Ceres can also get energy from solar energy, because it is only 2.8 astronomical units away from the sun. In contrast,EuropaandEnceladusFar away, 5.2 and 9 respectivelyAstronomical unit。
Ceres is located in the asteroid belt between the orbits of Mars and Jupiter. Previous studies have confirmed that there is a large amount of ice inside Ceres.ESA reported in Nature that they usedHerschel telescopeFirst discovered on CeressteamThe water vapor comes from the darker areas on the surface of Ceres.The amount of water vapor is not large, about 6 kilograms per second, but this discovery is of great significance for confirming that there is water on Ceres.The researchers speculate that there may be two specific reasons for the water vapor emission: one is that the ice on the surface of Ceres is rapidly heated by the sun, and the other is that there is still energy inside Ceres.Scientists speculate that there may beocean。
On December 18, 2014, Li Jianyang, a scientist at the American Institute of Planetary Sciences, said: "I don't think Ceres is inferior to other potentially livable planets in astrobiology. Life requires three basic conditions - liquid water, energy sources and some chemical components (carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur), and Ceres has certain advantages."[16]
Discovery process
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Ceres
In 1766, there was a German man named John·Titius(Johann Daniel Titius)series：
（0+4）/10=0.4；（3+4）/10=0.7；（6+4）/10=1.0
（12+4）/10=1.6；（24+4）/10=2.8；（48+4）/10=5.2
（96+4）/10=10→（3*2ⁿ+4）/10
To Titius' surprise, he found that each item in this series was related to the six known planets (i.eMercury, Venus, Earth, Mars, JupiterSaturn）The ratio of distance to the sun (the distance from the earth to the sun is set as 1 unit) has a certain relationship.
Titius's friend, astronomerBodeDeeply aware of the significance of this discovery, he announced the discovery of Titius in 1772, which attracted great attention from scientists;And called Titius Bode's LawSolar system planetsAverage distance from the sun
At that time, people had not foundUranus、NeptuneThat Saturn is the planet farthest from the sun.
Ceres rushes to the sun
In 1781, British Germanherschel At the position close to 19.6 (i.e. the eighth item in the sequence)UranusFrom then on, people must be convinced of this.According to this rule, the position of 2.8, the fifth item in the series, should also correspond to a planet, but it has not yet been found.As a result, many astronomers and amateur astronomers set out on the journey to find this new planet with great enthusiasm.
On the New Year's Eve of 1801, an Italian priestGiuseppe Piazzi (Giuseppe Piazzi, July 7, 1746~July 22, 1826)concentrate one's attention onAnd observed the starry sky.Suddenly, he found a very small star in his telescope, just at the position 2.8 in the Titius Bode rule.This planet has been changing its position during several days of observation.However, when Piazzi wanted to further observe the asteroid, he fell ill.When he recovered and tried to find the asteroid again, it disappeared.Piazzi did not give up this opportunity. He thought that this might be the planet that people had never discovered.
Astronomers hold different views on Piazzi's discovery.Some people think Piazzi is right;Others think it may be acometThere are many opinions about this planet, and the astronomical community has many discussions.
A few months passed, and people's arguments were still unresolved.However, this debate attracted the attention of German mathematician Gauss.Gauss thought that since astronomers could not find Ceres through observation, could they find it through mathematical methods?Many astronomers don't think highly of Gauss's idea.Astronomers can't find Ceres. Can Gauss figure it out?His friends also advised him not to waste his time and talents on this hopeless problem.
Ceres
Young Gauss has his own opinion.He believed that astronomy could not be separated from mathematics.Without solid mathematical knowledge, it is impossible to become an excellent astronomer.This is also true in the history of astronomy.KeplerIt was with his mathematical ability that he discoveredThree laws of planetary motion。NewtonIt was also discovered with profound mathematical knowledgeLaw of universal gravitation。
stayGaussianBefore, famous mathematiciansEulerA method for calculating the orbits of planets has been developed.However, this method is too troublesome.Gauss was determined to find an easy way.On the basis of predecessors, Gauss created a new planet with his outstanding mathematical ability after hard calculationTrack calculationTheory.Based on Piazzi's observation data, using this method, he calculated the orbital shape of Ceres in only one hour, and pointed out when it would appear in which sky.
On the night of December 31, 1801, German astronomer Obers aimed his telescope at the sky at the time predicted by Gauss.As expected, Ceres appeared miraculously again!
Ceres
Gauss's calculation method is successful.The planet Gauss found on his pen tip has become the best New Year gift for mankind after hiding for a whole year.This gift shows the great role of mathematics in scientific research.
Before the discovery of the asteroid, Piazzi had been looking for Francis Wollastonfixed starMayer 87 star recorded in the list, but he could not find it at the position described in the table.Later, he found a moving star. At first, he thought it was a comet.
Piazzi continued to observe until February 11, but his discovery was not noticed. After that, the asteroid had already turned to the back of the sun and could not be observed.Later, German mathematician Gauss estimated its orbit based on Piazzi's three observations, and the following year, Franz Xaver, Baron von Zach and Obers successfully recovered the object.Another astronomer Bode believes that there should be planets between the orbits of Mars and Jupiter, and Ceres is the unknown planet he thinks, but its volume is larger than other planetsMegaplanetsMuch smaller, soWilliam Herschel (Friedrich Wilhelm Herschel, November 15, 1738~August 25, 1822) Later, he called this kind of celestial body "asteroid" and extended a standard, that is, to determine whether a celestial body is a planet, the volume of this planet must be larger than Ceres.
Ceres
Astronomical observation
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Ceres
When Ceres rushes near the perihelion, its apparent magnitude can reach+6.7. It is generally believed that such luminosity is too dark for the naked eye to see, but observers with special sharp eyesight may see this stardwarf planet。Ceres has an apparent magnitude of+6.73 on December 18, 2012.Asteroids whose brightness can reach this levelVesta、Zhishen Star(Flushing at rare perihelion) andRainbow God Star[64]。The luminosity of Ceres when it is combined is+9.3, which is equivalent to using 10X50BinocularsThe darkest object visible.Therefore, whenever he is on the horizon, as long as the sky is dark enough, he can see it with binoculars.
On June 25, 1995,Hubble Space TelescopeThe ultraviolet ray observation of 30% obtained an image with a resolution of 50 km.
In 2002,Keck telescopeuseadaptive optics Get infrared images with a resolution of 30 kilometers.
At the end of 2003 and the beginning of 2004,Hubble Space TelescopeThe appearance of Ceres was taken for the first time, and it was found that it was quite spherical, and the surface had different albedos. It was believed that Ceres had complex terrain, and some astronomers even speculated that Ceres had an icy mantle and a metal core.
Ceres Surface Mountains
Used in 2003 and 2004Hubble Space TelescopeThrough observation, the visible light image with a resolution of 30 km was obtained (the best data).
In 2015, NASA's“Dawn ”The probe is still running in the orbit of Ceres. Scientists found that there is a huge mountain range on Ceres, which looks like the pyramids in Egypt from the appearance.The height of the Pyramid Mountains is 6000 meters. There are also some huge impact craters, including the Occator impact crater in the northern hemisphere and the Urvara Yalode basin in the southern hemisphere.[2]
Planetary exploration
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Dawn
On February 19, 2015, Dawn captured the full picture of Ceres at an altitude of 46000 kilometers, and scientists found a mysterious bright spot in the image.In the latest mission, NASA has listed the mysterious bright spot as one of the primary observation targets. Some studies believe that it is the reflection of the ice material on Ceres.
The Dawn probe is using an ion thruster to enter a circular orbit with a radius of 13000 kilometers. At this height, the scene of the ice and rock crater on the surface of Ceres can be observed, so the mystery of the mysterious bright spot will also be revealed.
Although Dawn has lowered its orbit, it is still unable to image until the sun shines again on the surface of Ceres below the detector.Among many fascinating observation targets, mysterious highlights are very eye-catching.The Hubble Space Telescope observed Ceres 10 years ago, but only now have we obtained the clearest image of Ceres.This orbital adjustment of Dawn will continue until April 14, and a navigation and positioning will be carried out after the completion of orbit change. After that, we will conduct a comprehensive observation of Ceres and uncover various mysteries on Ceres.
Ceres has a diameter of about 950 kilometers, which is similar to Earth or other terrestrial planets because its equator is wider than the distance between the north and south poles.After April 23, Dawn will arrive at the RC3 orbit as planned, which is a new circular orbit, and begin a one-year exploration to take tens of thousands of images of the surface of Ceres.In fact, "Dawn" is still faulty. Two of its four reaction wheels have been damaged. Scientists stabilize the state through the gyroscope, which will cause "Dawn" to lose some of its original planned tasks.
On the RC3 orbit, each pixel can cover the surface area of Ceres with a span of 1.3 kilometers. At present, the best photo resolution is only 4.3 kilometers. Therefore, if you want to take better photos, you need to use reflected light at an appropriate angle to improve the clarity of the photos.As of April 7, the detector has formed an isosceles triangle with the sun and the earth, with a distance of 2.89 astronomical units.[1]
"Dawn" was launched in 2007. Its main goal is to visit Vesta and Ceres, two major objects in the asteroid belt.Dawn entered the orbit of Vesta in 2011, left Vesta in 2012, and reached the orbit of Ceres in 2015.NASA said that on October 31 and November 1, Dawn did not communicate with ground controllers through the Deep Space Network as planned.After analysis, the project scientist believes that the "loss of connection" is because the fuel of the detector has been exhausted, and it can no longer adjust and control its antenna for normal communication, nor can it adjust its solar panel to charge towards the sun.On November 4, 2018, NASA's Dawn asteroid probe recently lost contact with ground controllers.The project scientists said that Dawn had died of fuel exhaustion.
"Dawn" probe is driven by advanced ion thrusters, and its flight mileage has reached 6.9 billion kilometers so far.It is the first unmanned probe to visit two celestial bodies in the solar system.In its press release, NASA said that the observational images and data it sent back about Vesta and Ceres are crucial for understanding the history and evolution of the solar system.[15]
Detection history
Dawn
In 2006, the International Astronomical Union redefined Ceres asdwarf planetCeres was once considered to be the largest asteroid known in the solar system.
Ceres photographed by Dawn on January 25, 2015
On September 27, 2007, NASA launchedDawn Spacecraft, detected in 2011VestaAnd then arrived at Ceres in 2015. So far, no spacecraft has ever visited Ceres. The Dawn spacecraft carrying out this task will first enter the orbit of 5900km high to orbit around Ceres. After five months of research, the spacecraft will first reduce the height to 1300km, and then after five months to 700km.The instruments carried by the spaceship include frame camera, visible light and infrared lightSpectrometerGamma ray and neutron detectors.These will be used to examine the shape and element abundance of the dwarf planet.The observation of the perturbation of Mars induced by the motion of Ceres from the radio signals sent by spacecraft orbiting on the surface of Mars and in orbit has been used to estimate the mass of Ceres.
In January 2014, a new study by the European Space Agency confirmed for the first time that water vapor was emitted from Ceres.
In January 2015, Dawn was emerging from the back of the sun (it was once on the other side of the line between the earth and the sun, and could not communicate with the earth), and reestablished radio contact with the earth.
The engineers have programmed the next phase of the orbiting mission, which is called the Ceres approach phase.Dawn is about 640000 kilometers away from Ceres, approaching at a speed of 725 kilometers per hour.Next, when "Dawn" entered the orbit of Ceres, it marked that humans successfully flew around two celestial bodies with one detector (previously, "Dawn" had completed the mission of flying around the "Vesta" and successfully escaped from the constraints of gravity).[3]
Ceres photographed by Dawn on February 4, 2015
Dawn probe will soon enter the vicinity of Ceres. Scientists believe that there is a rocky surface on Ceres. What are those curious white patches?Some studies have also pointed out that white patches may be formed on the surface of Ceres when groundwater escapes into space. Scientists are expected to find a large area of ice on Ceres. NASA's exploration of Ceres will be a new milestone.
On January 27, 2015, NASA released the picture of Ceres taken by Dawn on January 25. The picture was 147000 miles (237000 kilometers) away from Ceres when it was taken, about 43 pixels wide, and 30% higher resolution than the pictures taken by the Hubble Space Telescope in 2003 and 2004.[4]
Picture of Ceres on February 12, 2015
On February 5, 2015, NASA released the picture of Ceres taken by Dawn on February 4, which was 90000 miles (145000 kilometers) away from Ceres.[5]
On February 17, 2015, NASA released the picture of Ceres taken by Dawn on February 12, which was 52000 miles (83000 kilometers) away from Ceres.[6]
Picture of Ceres on February 19, 2015
On February 25, 2015, NASA released the picture of Ceres taken by Dawn on February 19, which was 29000 miles (46000 kilometers) away from Ceres.[7]
On February 27, 2015, NASA released the moving picture of Ceres taken by Dawn on February 19.[8]
Kinematic picture of Ceres on February 19, 2015
Photos taken 40000 km away from Ceres on February 25
Ceres photographed by Dawn on March 1
At 07:39 on March 6, 2015 (20:39 Beijing time), Dawn began to be captured by the gravitational field of Ceres. At this time, the spacecraft was about 61000 kilometers away from Ceres.[9]
Later, JPL received the signal from the spacecraft at 8:36 a.m. EDT (21:36 p.m. Beijing time), confirming that Dawn spacecraft was in normal condition and its installed ion engine was also working properly. The spacecraft successfully entered the orbit around Ceres, becoming the first dwarf planet satellite.
This is the flight path of the spacecraft when Ceres captured Dawn
The mission originally planned to fly over Zhishen in 2018 was unable to go due to previous failures (ion engine failure delayed the voyage), and Dawn will fly around with Zhishen all the time.
Photos of Ceres on April 14 and 15, 2015
In July 2015, the topographic map of Ceres.
On April 20, 2015, NASA released the pictures and moving pictures of Ceres taken by Dawn on February 14 and 15, 14000 miles (22000 kilometers) away from Ceres.[8]
Kinematics of Ceres on April 14 and 15, 2015
In November 2018, NASA's Dawn mission ended and lost contact with ground controllers.[15]
geographical position
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The classification of Ceres has been changed many times, and it is caused by disagreement among astronomers.John Bode believed that Ceres was the "missing planet" between Mars and Jupiter, 419 million kilometers (2.8AU) away from the sun.Ceres was given the symbol of a planet,Unicode is U+26B3[17]Before more asteroids were discovered, Ceres (also known as Wisdom, Marriage and Vesta) had been listed as planets in astronomy books for nearly half a century.
However, when other celestial bodies are found in the same range, people gradually understand that Ceres is just one of many similar types of celestial bodies.William Herschel created the term asteroid (planet like body) in 1802 to call this kind of body, and wrote that "it is so difficult to distinguish from stars, and the best telescope will also think it is an asteroid".As the first asteroid discovered, it is listed as Asteroid 1 Ceres in the modern asteroid numbering system.
In 2006, the debate about whether Pluto is a "planet" triggered the question of whether Ceres should also be reclassified as a planet.Before the International Astronomical Union officially defined the planet, the planet was defined as "a celestial body that: (a) has enough mass to overcome the rigid force with its own gravity, so it can show the shape of hydrostatic equilibrium (close to a sphere); (b) revolves around a star in orbit, and is not a planet or planet's satellite".According to this definition, Ceres would be the fifth planet in order from the inner side of the solar system.However, this definition was not accepted, and a new definition came into effect on August 24, 2006: "A planet meets (a) and (b), and the objects in the adjacent orbit must be cleared".According to this definition, Ceres is not a planet (because its orbit in the asteroid belt is full of thousands of asteroids), and it is classified as a "dwarf planet" (Pluto and Eris are also included), but it does not indicate whether it is still an asteroid.Astronomy also has asteroid belt comet, which is a dual identity object, so it is not ruled out that onedwarf planetThere can be other names.
Ceres is the largest object in the asteroid belt so far, but with the discovery of the Keppel belt and its objects, objects larger than Ceres have also been found, including (28978) asteroids (Ixion), (50000Quaor star）(Quaoar), asteroid (Orcus) and 2003 UB313（Eris ）And the newly discovered farthest object (90377)Sedna(Sedna) may also be larger than Ceres, and it may come from the inner layer of the Oort Cloud.PlutoSometimes it is also considered asKeppel Belt Objects。
Ceres has an orbit between Jupiter and Mars, located in theMain beltEvery 4.6 years, the earth circles the sun.The track is slightly tilted（i=10.6 °, Mercury for comparison has 7 °,Pluto17 °) andEccentricity（e=0.08, Mars for comparison is 0.09).
In the illustration, the orbit of Ceres (blue) and the orbits of some planets (white/gray) are shown. The orbits below the ecliptic are darker, and the position of the sun is indicated by an orange plus sign.The top left is an aerial view from the pole. Ceres's orbit is in the gap between Mars and Jupiter;The top right is a close-up picture, which shows the perihelion (q) and aphelion (Q) of Mars and Ceres, and the perihelion andAsteroid beltMajor asteroids, includingZhishen StarandHygiea , on both sides of the sun;The following figure is a perspective view showing the orbital inclination, comparing the orbits of Ceres and Mars with those of Jupiter.
In the past, Ceres was recognized asAsteroid familyThe largest asteroid in China.The asteroids in this family share similar orbital elements, indicating that these asteroids have a common origin and were formed after collision at a certain time.However, it is found that the spectral characteristics of Ceres are different from other members of the family, so the family has changed its name toGifian, named after 1272 Giffeon, the smallest in the family.Ceres seems to be the intruder of this family. It happens to have similar orbital elements, but the sources are different.
Ceres' rotation period (Ceres Day) is 9 hours and 4 minutes.
Origin and evolution
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Ceres may still existProtoplanet(The budding planet), formed in the asteroid belt 4.57 billion years ago.Although most of the protoplanets in the inner solar system, including all (moon Mars sized objects), are either merged with other protoplanets to become earth like planets, or ejected outside the solar system by Jupiter,Ceres is believed to be relatively intact (another possible protoplanet is Vesta, which is smaller in size and suffered a major impact after solidification, losing~1% of its own mass). An alternative theory is that Ceres was formed in the Kuiper Belt and later migrated to the asteroid belt.
The geological evolution of Ceres depends on the heat sources available during and after its formation: friction from the accretion of microstars, various radioactive elements, possibly including elements with short half-life (such as Al).These are believed to have been enough to differentiate Ceres into a rock core and an ice mantle shortly after its formation.This process may lead to the surface being reshaped by water volcanoes and geological structures, eliminating the ancient geological features.Because of its small size, Ceres will cool faster and effectively prevent the process leading to early geological restructuring.Any ice on the surface will gradually sublimate, leaving various hydrated minerals, such as clay and carbonate.
Today, Ceres seems to be a geologically inactivecelestial bodies, the surface may be affected by impact.A lot of water ice exists in its composition, so there may be a layer of liquid water in Ceres. This hypothetical layer may be called ocean.[10]If there is a layer of liquid water, it is believed that it will exist between the core of the ancient body and the ice mantle, just like the ocean in Europa in theory.The existence of the ocean is more likely to dissolve solutes (i.e. salt, ammonia, sulfuric acid or other antifreeze ingredients) in its water.
Mysterious highlights
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Ceres
Several mysterious bright spots on the surface of Ceres may eject steam plumes into space, suggesting that the dwarf planet has very active geological activities.
NASA's Dawn probe took some images when it approached Ceres. Scientists pointed out at the Lunar and Planetary Science Symposium that the latest images showed that the bright spot of Ceres may be ice water material, which will provide important clues to reveal the hidden material below the surface of the planet.
Dr. Andreas Nathues of the Max Planck Institute of Solar System in Germany said: "This kind of plume changes constantly throughout the day of Ceres. During the daytime, the plume will become brighter. At dusk, the plume will become dark, and in the evening, the plume will disappear completely."
At first, the mysterious bright spots discovered by the Hubble Space Telescope reappeared in the recent images taken by the Dawn probe. Although scientists suspect that these bright spots contain highly reflective ice water substances, the Dawn probe has not yet made full observation at close range. The latest data shows that these bright spots are likely to be ice water.
At present, the brightest bright spot is called "No. 5 feature" by scientists. Photos taken from different times and angles during the day show that it is probably related to plume materials. This area is located at the bottom of an 80 km diameter crater."We think this bright spot is some kind of gas release phenomenon, and we need high-resolution image data to confirm it," said Nathans
Not everyone quickly accepted the preliminary explanation of the plume. Bill McKinnon of the University of Washington said that you have never seen a plume with bright spots. Frost and snow fall on the surface of Ceres, but we need to further observe.
Ceres is a large, round and rich in water. It is a strange object in the asteroid belt. Scientists suspect that Ceres has a subsurface ocean or frozen water layer. As a dwarf planet, it is more like a planet or an ice satellite than an asteroid that astronomers had previously understood.[11]
Color photograph
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Color photo of Ceres surface
On April 6, 2015, the Dawn probe launched by NASA successfully reached the orbit of Ceres after nearly eight years of interstellar exploration, more than 5 billion kilometers.Today, NASA officially released the color photos of the surface of Ceres taken by Dawn.[12]
This is a recent picture of Ceres sent back by Dawn.Through the color of the picture, scientists can analyze the different material structures on the surface of Ceres, thus inferring the evolution process of this dwarf planet with a diameter of 950 kilometers.Although Ceres was discovered 200 years ago, no probe has ever visited it before.Therefore, the "Dawn" project is expected.
Latest findings
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Ceres
On June 19, 2015, according to foreign media reports, NASA's Dawn has made a new discovery on Ceres.Ceres is located inMarsAndJupiterThe largest body in the asteroid belt between.
Earlier this year, Dawn began its journey towards Ceres.The detector then found a mysterious reflection point with a huge area on the huge crater, which is generally believed to contain a large amount of water, ice or mud.
Many observers speculate that the bright spot on Ceres may be the evidence of aliens staying on this dwarf planet at present or in the past.Now, the probe has approached the object at a distance of 2700 miles.Although it is still unclear what the reflection point is, Dawn has observed more bright spots, and there is also a pyramid shaped object, which NASA predicts is 3 miles high.The photo was taken on June 6 and released on Wednesday.
Perhaps Ceres is very attractive to some unknown life forms both now and in the past.
We are looking forward to further data from Dawn in order to find out what exists on Ceres.
On February 18, 2017, it was reported that the Dawn detector on its way to Ceres made an amazing discovery - using the detector's visible and infrared spectrometers, they found the existence of simple organic matter on the surface, which was distributed in and around a crater named Ernutet, covering an area of about 1000 square kilometers.Considering that scientists did not expect to find organic matter at all, this is quite a large amount.The spectrometer is looking for carbon hydrogen bond, and it is speculated that the most compounds on the surface should be methyl and methylene compounds.Scientists speculate that they were generated on Ceres itself, rather than transported to the surface of Ceres by other stars.We already know that Ceres has a lot of water reserves. With carbonic compounds and soil, it is possible to move towards more complex organic compounds under sunlight.[13]
Mysterious bright spots on the surface of Ceres may be water ice in the crater ice trap
According to the Daily Mail of Britain, the dwarf planet has changed significantly due to the gravity of Jupiter and Saturn, as well as the inclination of Ceres' axis.At present,scienceScientists found the mystery of the formation of mysterious bright spots in Ceres crater. In a new study, NASA researchers found that some of the sedimentary materials formed by bright spots were probably water ice. It was speculated that they were formed during the period of maximum axis inclination of Ceres and long-term failure to shine sunlight in the crater[14]。
