On July 26, 2021, NASA announced that astronomers first detected Ganymedesteam[7]。In January 2024, the research results published in the journal Nature Astronomy showed that the scientific research team of the Italian National Institute of Astrophysics (INAF)NASA(NASA) Juno Jupiter probe successfully found mineral salts andOrganic compoundEvidence of existence.
Ganymede issolar systemThe largest satellite in.Diameter greater thanMercury, with a mass of aboutMercuryGanymede is mainly composed ofsilicateIt is composed of rock and ice. The star is obviously stratified, and has an iron rich and fluid core.Volume greater thanMercury, Yessolar systemThe only satellite known to have a magnetic loop in the.Ganymede was not first discovered by Galileo.Between 400 BC and 360 BC (most likely in the summer of 364 BC)《Tang Kaiyuan Zhanjing》Quote GanderJupiterAs Shi said, "If there is a small red star attached to its side", a famous historian of astronomyXi ZezongSir pointed out that:GanderThe last moon of Jupiter was observed in the middle of the 4th century BCEuropa。However, the discovery of Jupiter's satellite was made by Italian scientists after the telescope was invented in the early 17th centuryGalileo(Galilei) discovered it in 1610 when he observed Jupiter with it.Gander had been Galileo for nearly 2000 years, and he found it with the naked eye without a telescopeJupiterOfsatelliteThis is really a miracle.Later, the astronomer Simon Marius used Zeus's lover in Greek mythologyGanimedesName it.VoyagerThe spacecraft accurately measured the size of the satellite,GalileoThe detector found its underground ocean and magnetic field.
On March 12, 2015,NASAIt was announced that Ganymede, the largest satellite in the solar system, has a salt water ocean under the ice cover, with liquid water content exceeding that of the Earth.[1]
Star naming
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Between 400 BC and 360 BC (most likely in the summer of 364 BC)GanderGanymede has been discoveredGalileoMore than 2000 years earlier.
Ganymede captured with the Hubble telescope
On January 11, 1610,Galileo Galilei Three stars near Jupiter were observed;The next night, he noticed that the three stars had shifted, and then he found a fourth star, Ganymede.By the evening of January 15, 1610, Galileo had determined that these stars were orbiting Jupiter.He claimed that he had the right to name these satellites and considered the name of "Cosmian Stars", but eventually named them "Medicean Stars",
French astronomer Nicolas Claude Fabry de Perest suggestedMedici The satellites of the satellite family were named separately, but their suggestions were not adopted.Originally claimed that he first discovered the Galileo satelliteSimon Marius They tried to name these satellites "Saturn of Jupiter", "Jupiter of Jupiter", "Venus of Jupiter" and "Mercury of Jupiter", but they were never adoptedZeus' loverGeinimideName it.This nomenclature was not widely accepted for a long time, but was not widely used in early astronomical literature until the middle of the 20th centuryRoman numeralsAs a reference (the system was proposed by Galileo), it is called Jupiter III or "the third satellite of Jupiter".Later, with the discovery of Saturn's satellite group, the naming system proposed by Kepler and Marius began to be used to refer to Jupiter's satellites.Ganymede isGalileo satelliteThe only one named after a male character,
Ganymede is the only known satellite in the solar system that has a magnetic circleMagnetic coilIt may be caused by the convection movement of iron rich flow core.A small number of magnetic circles intersect with Jupiter's larger magnetic field, resulting in outward spreading field lines.Ganymede has a thin oxygen atmosphere, which contains atomic oxygen, oxygen andozone, simultaneouslyAtomic hydrogenIt is also one of the components of the atmosphere, and whether Ganymede hasthe ionosphereNot yet determined.Ganymede is mainly composed of silicate rocks and ice bodies. The star has obvious stratification, and has an iron rich and fluid core.Scientists speculate that there is a salt water ocean sandwiched between two layers of ice 200 kilometers below the surface of Ganymede.The surface of Ganymede has two main topographies: the darker area accounts for about one-third of the total area of the star body, which is densely covered with impact craters, and the geological age is estimated to be 4 billion years;The rest of the area is bright and crisscrossed with a large number of grooves and ridges, whose geological age is slightly younger than the former.The cause of the broken geological structure in the bright area is still a mystery, which may beTidal heatCaused by tectonic activities.
Internal structure of Ganymede: the average density of Ganymede is 1.936g/cm ³, which indicates that Ganymede is composed of nearly the same amount of rock and water, the latter mainly exists in the form of ice.The mass of ice body accounts for 46-50% of the total mass of satelliteGanymedeSlightly lower.In addition, there may be some unstable ice bodies, such asammoniaIce body.The exact composition of Ganymede rocks is unknown, but it is likely to be close to the L-type or LL typeOrdinary chondrite, these two types of meteoritesH Chondrite, containedAll ironAnd metal iron is less, while iron oxide is more on Ganymede. In terms of mass, the abundance ratio of iron and silicon is 1.05-1.27, while in the sun, it is 1.8.
The albedo of Ganymede's surface is about 0.43.Ice water widely exists on its surface, with a specific gravity of 50-90%, much higher than the overall proportion.utilizeNear infrared lightSpectroscopy, scientists found strong absorption of ice water in 1.04, 1.25, 1.5, 2.0 and 3.0 μ m wavelength bands.The trench structure in the bright zone may contain more ice bodies, so it is relatively bright.In addition to water, yesGalileoAnd ground-based observation stationsnear infrared spectroscopyThe analysis of UV spectrum results also shows the presence of other substances, includingcarbon dioxide、sulfur dioxideAnd may also include cyanogen, bisulfate and variousOrganic compound。in additionGalileoIt was also found on the surface of Ganymedemagnesium sulphate、sodium sulphateThese salts may come from the ocean below the surface.
The surface of Ganymede is asymmetric: its side in the same orbital direction should be brighter than its side in the opposite orbital direction.This situation is similar toEuropa, andGanymedeThe situation is just the opposite.In addition, Ganymede seems to be rich insulfur dioxide。andcarbon dioxideThe distribution in the two hemispheres is relatively uniform, althoughpolar regions It was not observed.GanymedeImpact crater(except for one) not richcarbon dioxide, which is also related toGanymedeDifferent.Ganymede's carbon dioxide may have been exhausted in the past.
internal structure
Internal structure of Ganymede
The stratigraphic structure of Ganymede has been fully differentiated, and it containsFerrous sulfideThe core is composed of iron, the inner ground culvert is composed of silicate, and the outer ground culvert is composed of ice.This structure is obtained byGalileoGanymede's own lowerDimensionlessMoment of inertia——The value of 0.3105 ± 0.0028 supports that Ganymede is actually a solid object with the smallest moment of inertia in the solar system.The intrinsic magnetic field of Ganymede detected by Galileo is related to its iron rich and flowing core.Convection of liquid iron with high conductivity is the most reasonable mode to generate magnetic field.
The thickness of different layers inside Ganymede depends onsilicateOf which some areolivineandpyroxene）And the amount of sulfur in the core.The most likely case is that the core radius reaches 700-900km, the thickness of the outer ice culvert reaches 800-1000km, and the rest issilicateTexture culvert.The density of the core is 5.5 – 6g/cm ³, and the density of silicate texture culvert is 3.4 – 3.6g/cm ³.Similar to the structure of the earth's core, somemagnetic fieldThe model required in iron-Ferrous sulfideThere is also a solid core made of pure iron in the liquid core.For this type of core, the maximum radius may be 500 km.The temperature of Ganymede's core may be as high as 1500-1700K, and the pressure may be as high as 100 kilobars (10 billion pascals).
Ganymede contains the most liquid water in the solar system.hubble space telescope By analyzing Ganymede's auroraspectrumIt is estimated that its ocean depth is 400 kilometers.Other scientists suspect that this may be just a small part of Ganymede's ocean. Ganymede may have three oceans, which are stacked layer by layer. Each layer has a depth of 400 kilometers and is separated by a high-pressure ice layer. The lowest layer of ocean may directly contact the rock core of Ganymede.Therefore, Ganymede's ocean depth may exceed 1000 kilometers, containing a huge water body of more than 15 billion cubic kilometers, whose water content is more than 30 times that of the Earth.
Surface characteristics
Newly formed impact crater in trench terrain area
There are mainly two types of landforms on the surface of Ganymede: one is a very old dark area densely covered with impact craters, and the other is a slightly younger (but still very old in geological age) bright area with a lot of grooves and ridges.The dark area accounts for about one-third of the total area of the sphere, which contains clay andOrganic matterThis may be caused by the meteorite that hit Ganymede.However, the heating mechanism of trench terrain is still a major problem in planetary science.According to the present view, the trench terrain is essentially formed by tectonic activities;And ifIce volcanoIf it plays a role, it is only a secondary role.In order to cause this tectonic activity, Ganymede'slithosphereThe pressure must be strong enough, and the force that causes this pressure may be the same as that which happened in the pastTidal heatAction related - this action may generate gravity when Ganymede is in an unstable orbital resonance statetideThe bending action on the ice body will heat the interior of the star, exert pressure on the lithosphere, and further cause cracksHorstandGrabenThese terrains replaced the ancient dark areas that account for 70% of Ganymede's surface area.The formation of the trench terrain may also be related to the formation process of the early core and the tidal heat effect in the afterbody, which caused the phase transition of the ice body andThermal expansion and cold contractionIt may cause Ganymede to expand slightly, with an amplitude of 1-6%.With the further development of stars, hot water jets are squeezed from the core to the surface of stars, leading to structural deformation of the lithosphere.The heat generated by the radioactive decay inside the star is the most likely heat source, and the formation of Ganymede's underground ocean may depend on it.Through studying the model, people found that if Ganymede'sEccentricity of trackThe value is much higher than that of today (in fact, it may also be so), so tidal heat may be replaced by radioactive decay heat source, and become the main heat source of Ganymede.
It can be seen in both landforms, but it is more densely distributed in the dark area: this area has experienced large-scale meteorite bombardment, so the distribution of impact craters is saturated.There are fewer impact craters in the brighter trench terrain area, where the terrain developed due to structural deformation has become the main geological feature.The density of the impact crater indicates that the geological age of the dark area has reached 4 billion years, which is close to the geological age of the highland terrain on the moon;However, the trench terrain is slightly younger (but it cannot be determinedExact age）。Similar to the moon, Ganymede experienced a period of violent meteorite bombardment 3.5 to 4 billion years ago. If this is true, then there was a large-scale bombardment event in the solar system during this period, and after this period, the bombardment rate was greatly reduced in the bright area, both the impact crater covering the trench and the trench cutting the impact crater,This shows that some of the trenches are also very old in geological age.There is also a relatively young impact crater on Ganymede, and its outward radiation is still clearly visible.The depth of Ganymede's impact crater is not as deep as that on the moon and Mercury. This may be because Ganymede's ice texture layer is weak and will shift, which can transfer part of the impact forceGeologic AgeThe pit structure of the ancient impact crater has disappeared, leaving only one kind ofVariational complementary structure(English: palimpsest)
Prominent features of Ganymede include a dark plain called Galileo region, in which grooves are distributed in concentric rings, which may be formed during a period of geological activity.Another notable feature is Ganymede's two polar crowns, which may be composed of frost.This frost extends to the area with latitude of 40 °.VoyagerThe polar cap of Ganymede was discovered for the first time.At present, there are two theories to explain the formation of the polar cap. One is that it is caused by the diffusion of ice at high latitudes, and the other is that it is from outer spacePlasma stateProduced by ice bombardment.The observation results of Galileo are more inclined to the latter theory,
Atmosphere and ionosphere
In 1972, a group ofIndonesiaWorked at Boscha ObservatoryIndia、britainandU.S.AThe joint team of astronomers announced that they had detected Ganymede's atmosphere during a occultation, whenJupiterFrom afixed starPreviously passed.They estimated the atmospheric pressure to be about 1 microbar (0.1 Pa).In 1979, Voyager 1 flew byJupiterAt that time, similar observations were made with the help of a occultation at that time, but different results were obtained.Voyager 1's occultation observation method usesFar ultravioletSpectral observation, compared with the 1972Visible spectrum observation method, is much more accurate in determining the presence or absence of gases.Voyager 1The observation data of Ganymede show that there is no atmosphere on Ganymede, and the maximum particle number density on its surface is only 1.5 × 10 ⁹ cm ³, and the corresponding pressure is less than 2.5 × 10 ⁹ microbar.The latter data is five times smaller than that in 1972Order of magnitude, indicating that the early estimates were too optimistic,
The false surface of GanymedeColor temperatureBut in 1995Hubble Space TelescopeIt is found that Ganymede has a thin atmosphere with oxygen as the main component, which is similar to the atmosphere of Europa.The Hubble Space Telescope detected the atmospheric light of atomic oxygen in the far ultraviolet spectrum of 130.4 nm to 135.6 nm.This atmospheric light is emitted when molecular oxygen is dissociated by electron bombardment, which indicates that Ganymede has a neutral atmosphere dominated by O ₂ molecules.The surface particle number density is within the range of 1.2-7 × 10 ⁸ cm ³, and the corresponding surface pressure is 0.2-1.2 × 10 ⁸ microbar.These values are within the upper limit of the values detected by Voyager in 1981.This micro level of oxygen concentration is not enough to maintain life;Its source may be the process in which the ice body on the surface of Ganymede decomposes into hydrogen and oxygen under the radiation, of which hydrogen escapes from Ganymede soon due to its low atomic weight.The atmospheric light observed on Ganymede is not generally distributed in space like the same phenomenon on EuropaHomogeneity。The Hubble Space Telescope has found several bright spots in Ganymede's northern and southern hemispheres, two of which are located in the 50 ° latitude area - GanymedeMagnetic coilDiffusion ofField lineThe junction with the gathering field line.At the same time, some people think that the bright spot may be the aurora formed by the plasma cutting the diffusion field line in the falling process.
Ionosphere should also exist on Ganymede due to the existence of neutral atmosphere, because oxygen molecules are exposed toUltraviolet radiationIonized by bombardment of high-energy electrons.But like the atmosphere, the nature of Ganymede's ionosphere is also controversial.Some observations of Galileo found thatelectron densityIt is high, indicating the existence of the ionosphere, but other observations show nothing.The electron density of Ganymede surface measured by various observations is in the range of 400-2500 cm ³.By 2008, the ionospheric parameters of Ganymede had not yet been accurately determined.
Another way to prove the existence of Ganymede's oxygen atmosphere is to measure the gas hidden in Ganymede's surface ice body.In 1996, scientists announced theozoneMeasurement results of.In 1997, spectral analysis revealed the dimer (or diatomic molecule) absorption function of molecular oxygen, that is, when the oxygen molecule is in theDense phaseThis absorption function will occur when the molecular oxygen is stored in the ice body, and the absorption function is the best.The position of the absorption spectrum of the dimer depends more on latitude and longitude than on the albedo of the surface - as the latitude increases, the position of the absorption spectrum will move up.On the contrary, the absorption spectrum of ozone will move down with the increase of latitude.The laboratory simulation test shows that, in the area where the upper surface temperature of Ganymede is higher than 100K, O ₂ does not aggregate, but diffuses into the ice body.
WhenEuropaAfter the discovery of sodium in Ganymede, scientists began to search for this substance in Ganymede's atmosphere, but in 1997 they found nothing.It is estimated that the abundance of sodium on Ganymede is 13 times smaller than that on Europa, which may be due to the lack of this substance orMagnetic coilPut theseHigh-energy atomIt's blocked.Another trace component in Ganymede's atmosphere is atomic hydrogen, which can be observed 3000 kilometers from the surface of the satellitehydrogen atomThe exists of.Its quantity density on the surface of the star is about 1.5 × 10 ≮ cm ³.
Magnetosphere
Between 1995 and 2000,GalileoA total of six close flybys of Ganymede revealed that the satellite has a permanent magnetic moment independent of Jupiter's magnetic field, which is estimated to be 1.3 × 10 ¹ ³ T · m ³, three times larger than Mercury's magnetic moment.The intersection angle between its magnetic dipole and Ganymede's rotation axis is 176 °, which means that its magnetic pole is facing Jupiter's magnetic field.MagnetosphericNorth magnetic poleLocated below the track plane.The intensity of the dipole magnetic field created by this long-term magnetic moment in the equatorial region of Ganymede is 719 ± 2 na tesla, which exceeds the strength of Jupiter's magnetic field here - the latter is 120 na tesla.Ganymede's equatorial magnetic field is facing Jupiter's magnetic field, which makesField lineReaggregation is possible.The magnetic field intensity in the north and south polar regions is twice that in the equatorial region, 1440 na tesla,
The long-standing magnetic moment delimits a space around Ganymede, forming a small one embedded in Jupiter's magnetic fieldMagnetosphere。Ganymede is the only known moon in the solar system that has a magnetosphere.Its magnetosphere diameter is 4-5 Rj (Rj=2631.2 km).The magnetospheric field line of Ganymede is closed in the region where the upper latitude of Ganymede is less than 30 °,charged particle(such as electrons and ions) are captured, forming radiation bands.The main ions contained in the magnetosphere are single ionizedOxygen atom——O+- This is consistent with the characteristics of Ganymede's oxygen bearing atmosphere.However, in polar regions with latitude higher than 30 °Field lineIt spreads outward, connecting Ganymede and Jupiter's ionosphere.High energy (up to tens or even hundreds of kilovolts) electrons and ions have been found in these areas, which may lead to the aurora phenomenon in Ganymede's polar region.In addition, the heavy ions falling in the polar region have sputtered and finally darkened the ice body on Ganymede's surface.
GanymedeMagnetosphereThe interaction with Jupiter's magnetic field is very similar to the interaction between the solar wind and the Earth's magnetic field in many aspects.As revolving around JupiterPlasmaThe bombardment of Ganymede's magnetosphere in the opposite orbital direction is very similar to that of the solar windGeomagnetic fieldThe bombardment of.The main difference is the speed of the plasma flow - supersonic on Earth and subsonic on Ganymede.Because its plasma flow velocity is subsonic, the magnetic field on Ganymede's side opposite to the orbital direction has not been formedBow shock。In addition to its inherent magnetosphere, Ganymede also has an inductiveDipole magnetic field, its existence is similar to Jupiter near Ganymedemagnetic field intensityChanges.With the change of the direction of Ganymede's inherent magnetosphere, the induced magnetic field alternately radiates toward Jupiter or away from Jupiter. The intensity of the magnetic field is one order of magnitude weaker than that of Ganymede itself - the formerMagnetic equatorThe field strength of the region is 60 Natesla, which is only half of Jupiter's field strength here.The induced magnetic field of Ganymede is very similar to that of Ganymede and Europa, which indicates that the satellite may also have a high conductivity underground ocean.Because Ganymede's internal structure is completely differentiated and has a metal coreMagnetosphereIt may be generated in a way similar to that of the earth's magnetic field: the coreMaterial movementResults.If the magnetic field is based on the principle of dynamo, then Ganymede's magnetosphere may be caused by the convection movement of its core components.
Although Ganymede is known to have an iron core, its magnetosphere is still mysterious, especially why other satellites of the same size do not have magnetosphere.Some studies believe that Ganymede's core should have been sufficiently cooled in such a relatively small volume that the flow of the core and the generation of the magnetic field are unsustainable.One explanation claims to cause starsSurface textureThe deformed orbital resonance can also play a role in maintaining the magnetosphere: Ganymede'sEccentricity of trackandTidal heatThe effect is increased due to the resonance of some orbits. At the same time, its mantle also acts as an insulating core, preventing its cooling. Another explanation is thatmantleThis magnetosphere is caused by the residual magnetism in silicate rocks.If the satellite once had a strong magnetic field based on the generator principle in the past, then this theory is likely to work.
Astral history
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The accretion process of Ganymede, probably caused by the accretion of Jupiter's secondary nebula, that is, the disk composed of gas and dust surrounding Jupiter after its formation, lasted for about 10000 years. It is quite different between the darker Nicholson region and the brighter Hapagia trough.
Compared toGanymede100000 years is much shorter.When Galileo began to form, Jupiter's secondary nebula contained relatively little gas;This has led to Ganymede's longeraccretion Time.On the contrary, since Ganymede was formed immediately after JupiterSub nebulaIt is also relatively dense, so its accretion time is relatively short.The relatively short formation time makes the heat generated in the accretion process less escape. These unexpired heat leads to the melting of the ice body and the differentiation of the internal structure of Ganymede: that is, the rock and ice body are separated from each other, and the rock sinks into the center of the star to form the core.In this respect, Ganymede is different from Callisto, which, due to its long formation time, leads to the escape of accretion heat, so it is unable to melt the ice body and differentiate the internal structure at the initial stage.This hypothesis reveals why the two satellites, whose mass and composition are so close, look so different.
After its formation, Ganymede's core also preserved most of the heat formed in the process of accretion and differentiation. It only slowly released a small amount of heat into the icy mantle layer, just like the operation of a thermal battery.Then, the mantle passes throughConvectionConducting heat to the surface of the star.Before longradioactive elementIt begins to decay, and the heat generated further heats the core, which intensifies the differentiation of its internal structure, and finally forms an iron-Ferrous sulfideThe core and a silicate mantle.So far, the internal structure of Ganymede has been completely differentiated.In contrast, the radioactive heat generated by Ganymede without internal structural differentiation can only lead to convection in its ice, which effectively cools the star and prevents large-scale ice melting and rapid differentiation of internal structure. At the same time, it can only cause partial differentiation of ice and rock at most.Today, Ganymede's cooling process is still very slow.The heat released from the core and silicate mantle enables the existence of the underground ocean on Ganymede. At the same time, the slowly cooling and flowing iron ferrous sulfide core is still promoting the thermal convection in the star body and maintainingMagnetic coilThe exists of.Ganymede's externalHeat fluxIt is probably higher than Ganymede.
Operation characteristics
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Track distance
Ganymede's orbit is 107400 kilometers away from JupiterGalileo satelliteThe third closest to Jupiter in the middle, its revolution period is 7 days and 3 hours.Like most known Jupiter's moons, Ganymede is also locked by Jupiter, always facing Jupiter on the same side,Io、EuropaLaplacian resonance state between Ganymede and Ganymede.itsEccentricity of trackVery small, and the orbital inclination is also very small, close to the equator of Jupiter. At the same time, the orbitalEccentricityAnd inclination angle will also bePeriodic functionThe form of is affected by the gravitational perturbation of the sun and Jupiter.The variation range is 0.0009-0.0022 and 0.05-0.32 °, respectively. The variation of this kind of track makes the inclination of its axis vary from 0 to 0.33 °.
Laplace resonance state
GanymedeEuropa、IoKeepTrack resonanceRelationship: that is, Ganymede rotates once every revolution, Europa rotates twice, and Io rotates around when Europa is nearArch pointWhen Io is at the apoapsis, there will be a convergence between the two;When Europa is at the periapsis, it will also close with Ganymede.Europa, Europa and Ganymede will move at the same speed, so there may be three-star convergence between the three.This complex orbital resonance is called Laplace resonance.The current Laplacian resonance cannot transform Ganymede'sEccentricity of trackPromote to a higher value.
Eccentricity
Eccentricity value of 0.0013 may be early residual - at that timeEccentricity of trackThe promotion of is possible.However, Ganymede's orbital eccentricity is still puzzling: if its eccentricity cannot be increased at this stage, it must indicate thattideUnder the effect of dissipation, its eccentricity value is gradually losing.This means that the last loss of eccentricity occurred hundreds of millions of years ago.Because the eccentricity of Ganymede's orbit is relatively low today - only 0.0015 on averageTidal heatIt should also be very weak.But in the past, Ganymede may have experienced one or more kinds of Laplacian resonance, so that its orbital eccentricity can reach a high value of 0.01-0.02.
This may have caused significantTidal heat effect；However, this multi-stage internal heating finally resulted in the groove terrain on the surface of Ganymede. People still cannot know exactly how the Laplacian resonance between Io, Europa and Ganymede was formed.Now there are two hypotheses: one is that this state existed at the beginning of the formation of the solar system;Another thinks that this state was developed after the formation of the solar system.One possible formation process is as follows: First, due to the tidal effect of Jupiter, the orbit of Io moves outward until a 2:1 orbital resonance occurs with Europa at some point;Then its orbit continues to move outward, and at the same time, part of the rotating torque is transferred to Europa, which also causes the latter's orbit to move outward;This process continues until Europa reaches a point where it forms a 2:1 orbital resonance with Ganymede.Finally, the position movement rate of the two pairs of superimposition phenomenon among the three is consistentLaplace resonance ，
Detection history
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Voyager
The first batch isPioneer 10 andPioneer 11 The information about Ganymede returned by the two is less.Then Voyager 1 and Voyager 2 flew past Ganymede in 1979.They measured its size accurately, and finally proved that its volume was larger than Titan, which was once thought to be larger than the former.In addition, the two spacecraft also found the trench terrain on Ganymede.
In 1995, Galileo entered orbit around Jupiter.Between 1996 and 2000, it made six close flybys of Ganymede.These six sweeps are named G1,G2，G7，G8，G28，G29。In its closest flyby, G2, Galileo was only 264 kilometers from the surface of Ganymede.In the G1 flyover in 1996, it discovered Ganymede's magnetic field.Later, Ganymede's underground ocean was discovered and announced in 2001.Galileo sent back a large number of spectral images and found several non ice compounds on the surface of Ganymede.The probe for close detection of Ganymede isNew Horizon NoIn 2007, it flew past Ganymede on its way to Pluto, and took a topographic map and composition map of Ganymede during its acceleration.
In February 2009,NASAAnd the European Space Agency confirmed that the plan will be implemented prior to the "Titan Saturn Plan".The Europa Jupiter program includes the "Jupiter Europa Orbiter" hosted by NASA and the "Jupiter Ganymede Orbiter" hosted by the European Space Agency, and may also includeJapan Aerospace Research and Development AgencyHosted by the "Jupiter Magnetic Field Probe".The cancelled orbit exploration plan of Ganymede isJupiter Icy Moons Orbiter 。Original planned useNuclear fissionThe reactor is its power source, which will enable it to carry out a detailed survey of Ganymede.However, due to budget cutting, the plan was cancelled in 2005.Another cancelled plan is called "The Grandeur of Ganymede".
On July 26, 2021, NASA announced that by looking at the data of the Hubble Space Telescope over the past two decades, researchers found that Ganymede's thin atmosphere contained water vapor.However, the water vapor may not come from the underground ocean, on the contrary, it may be ice evaporated from the surface of the satellite[7]。
In January 2024, the research results published in the journal Nature Astronomy showed that the scientific research team of the Italian National Institute of Astrophysics (INAF), with the help of the Juno Jupiter probe of NASA, successfully found evidence of the existence of mineral salts and organic compounds on the surface of Ganymede.At the same time, researchers pointed out that Ganymede has a thick ice shell, so the composition of the surface currently observed does not necessarily represent the chemical composition under the ice and inside it.The "Juice" probe launched by the European Space Agency in 2022 may provide more data information for Ganymede research.[8]
Subglacial ocean
On March 12, 2015, the National Aeronautics and Space Administration (NASA) announced that NASA's Hubble Space Telescope had recently observed the aurora phenomenon generated by Ganymede's magnetic field, and measured that there was a salt water ocean with a certain salinity under Ganymede's ice layer.
According to estimates, the depth of this underground ocean is about 100000 meters, which is more than 10 times that of the deepest ocean on the earth.It exists under the surface of the earth, which is 150 kilometers thick and mainly composed of ice.[2-4]
Impact on Jupiter
Ganymede, Jupiter's largest moon, is also the only one with a strong magnetic field.Using thousands of images obtained by the Hubble Space Telescope, scientists found that the spectacular aurora seen in Jupiter's polar region was formed under the gravitational influence of Ganymede's magnetosphere,
Ganymede and the very active Io will interact with the plasma of this planet when they orbit Jupiter, and produce bright spots in the polar region of Jupiter. These bright spots are called "auroral footprints".However, until now no one knows how big Ganymede's footprint is and why Ganymede will cause the beautiful and spectacular auroras in Jupiter's polar region.
The researchers measured the exact size of Ganymede's footprints by analyzing the pictures taken by the Hubble Space Telescope. They believed that the area of these spots was too large to be the projection of the satellite on the planet, and its diameter was very consistent with the diameter of Ganymede's protective magnetic field.The scientists also measured the size and shape of Europa's auroral footprints, which were caused by charged particles from the active volcanoes on Io
University of Liege Denis Grodent, an astrophysicist at the University of Liege, said: "Each of these auroral structures is telling us an ongoing story - large-scale energy transmission is taking place on the distant Jupiter.By analyzing the exact location of these auroras, and the changes in their shape and brightness when Io and Ganymede orbit Jupiter, we have made the most detailed simulation diagram so far to simulate the electromagnetic interaction between Jupiter and these satellites. "Gruntont introduced the research results in detail at the European Planetary Science Conference held in Germany,
In addition to combining Ganymede's auroral footprint with its magnetic field, Gruntont and his research team also found that the brightness of the satellite's auroral light was unexpectedPeriodic changeThese changes took place at three different times.Researchers believe that each change reflects the interaction between Jupiter's plasma and Ganymede's magnetic field, but they still do not know what causes this interaction,[5]
Full Map
Ganymede
Research leaderJohns Hopkins University Wes Patterson of the Applied Physics Laboratory said: "By drawing the surface map of Ganymede, we can more accurately answer the scientific questions about the formation and evolution of this truly unique satellite."
This map was created byUSGSAnnounced that Ganymede is the first complete cold exoplanet satellite map, which technically describes various geological features on the surface of Ganymede.Patterson, Collins and colleagues used NASA travelers and GalileoSpace probeThe captured image makes this map.
Ganymede
Since Ganymede was discovered in January 1610, it has become the focus of repeated observation.Scientists observed Ganymede with earth telescopes for the first time, and then observed it with spacecraft flying close to and around Jupiter.These studies have found a complex cold world.Its surface is characterized by a sharp contrast between the two main terrain types.These two landforms are dark and cold cratered areas and brighter and younger (but still very old) areas, which are characterized by a large number of grooves and ridges.
Ganymede
Ganymede is 3280 miles in diameter, larger than Mercury and Pluto, the dwarf planet.It is also the only known satellite in the solar system that has its own magnetosphere.This map details the geological characteristics of Ganymede's formation and evolution during most of the history of the solar system.These geological characteristics record the internal evolution of Ganymede, the interaction between Ganymede dynamics and other Galilean satellites, and the evolution of small bodies hitting Ganymede's surface.
Ganymede
This new map is an important tool for researchers to compare the geological characteristics of other icy satellites, because any feature type found on other icy satellites is similar to that of Ganymede somewhere.Ganymede's surface is more than half of all the land area of the earth.This satellite provides scientists with a variety of observation sites."Ganymede shows ancient and recently formed geological characteristics. In addition to geological diversity, it also increases historical diversity," Collins said[6]
Discovery significance
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Galileo discovered that other planets also have satellites, which confirmed that the earth is not the only planet in the universe that has satellites, and also proved thatNicolaus Copernicus "Heliocentric theory" is correct.
Using simple telescopes and relying on independent research, Galileo gave people a good understanding of the solar system, galaxies and the vast universe.The telescope made by him enables people to observe the space scenes that were difficult to observe before, and deepens people's understanding of the universe.
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The largest satellite in the world's solar system:The largest satellite is Ganymede, whose weight is 2.017 times that of the Earth satellite.Its average diameter is 5262.4 kilometers.(Guinness World Records)
