Enceladus isSaturnIs the sixth largest satellite in the solar systemsatellite。In 1789William Herschel Found.stayVoyagerDetected in the 1980sSaturnPreviously, people only knew that Enceladus was an ice covered moon.Voyager shows that Enceladus has a diameter of about 500 kilometers (equivalent to Saturn's largest moontitanOne tenth of its diameter), and its surface can reflect almost 100% sunlight.Voyager 1Found Enceladus orbiting SaturnE-ringThe densest part indicates that there may be some connection between the two;andVoyager 2It is found that although the satellite is small in size, the ancientImpact craterStructure, and there are relatively young distorted topographic structures caused by geological activities -Geologic AgeEven only 100 million years.[1]
In June 2023,Phosphorus, a key component of life, has been detected in the oceans of Enceladus[18]。
Enceladus isSaturnThe sixth largest satellite ofWilliam Herschel Found.stayVoyagerDetected in the 1980sSaturnPreviously, people only knew that Enceladus was an ice covered moon.Voyager shows that Enceladus has a diameter of about 500 kilometers (equivalent to Saturn's largest moontitanOne tenth of its diameter), and its surface can reflect almost 100% sunlight.Voyager 1Found Enceladus orbiting SaturnE-ringThe densest part indicates that there may be some connection between the two;andVoyager 2It is found that although the satellite is small in size, the ancientImpact craterStructure, and there are relatively young distorted topographic structures caused by geological activities -Geologic AgeEven only 100 million years.
To explore Enceladus, NASA launchedCassini spacecraft, and arrived near Saturn at the beginning of the 21st century, providing a lot of data for scientific research.The exploration shows that Enceladus is one of the three stars in the outer solar system where geological eruptions have been observed so far (the other two are Europa and Triton respectively).The analysis shows that the ejected material is liquid water below the surface of the star;At the same time, strange chemical components are also found in the ejected plumes, so Enceladus is also considered as an important research object of astrobiology.In March 2015, the University of Tokyo, Japan Ocean Research and Development Agency and other international teams in Europe and the United States found hot water on Enceladus.This is the first time that human beings have found the available resources outside the Earth in the solar systemlifeThe environment that exists.
On April 14, 2017, at 2:00 a.m. Beijing time, NASA held a press conference at the James Weber Auditorium in Washington headquarters, announcing that Enceladus has all the elements needed for life, while Europa, in a similar situation, also has potential.
Explore History
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On August 28, 1789,William Herschel When he first used his 1.2-meter telescope (the largest telescope in the world at that time), he discovered Enceladus in 1787,herschel The satellite has been observed through his 16.5cm telescope, but it was not confirmed at that time.Because Enceladus is badApparent magnitude(up to 11.7, etc.). At the same time, it is close to Saturn and its halo, which are much brighter. It is difficult to observe this satellite from the earth, only throughlensOnly telescopes with a diameter of 15-30 cm can observe it, which also depends on the local atmospheric conditions andlight pollutionDegree.As one of the many Saturnian satellites discovered before the space age, the best observation time for Enceladus is in the period of torus crossing. At this time, the tangent line of Saturn's ring perpendicular to the Earth's operating point can only be observed as a thin line on the Earth, and the brightness of Saturn's ring is greatly reduced, so it is the best time to observe Enceladus.
untilVoyagerAfter the implementation of the plan, the observation of Enceladus has been significantly improved, while the information previously available to scientists only includes the orbital characteristics of the satellite and the approximate estimates of its mass, density and albedo.
Enceladus photographed by Voyager 2 on August 26, 1981[2]
The first set of close ups of Enceladus was obtained by two tourist spacecraft, among whichVoyager 1It is the first man-made aircraft to pass by Enceladus, which passed at a distance of 202000 kilometers from Enceladus on November 11, 1980.Although the resolution of the image data obtained at this distance is low, it still shows that Enceladus has a surface with high albedo and lack of impact pits, which indicates that the geological age of the satellite's surface is low.Voyager 1 also confirmed that the orbit of Enceladus is located in the dense part of Saturn's E ring;Based on the analysis of the young surface of Enceladus, scientists involved in the Voyager Spaceship Program believe that the E ring is composed of particles ejected from the surface of Enceladus.Voyager 2On August 26, 1981, it flew by at 87010 kilometers away from Enceladus, thus obtaining clearer image data about the satellite. These data show many features of the satellite's young surface, and also show that the geological age of the satellite varies greatly in different regions.In the middle and high latitudes of the northern hemisphere, there are a large number ofImpact craterIn the area near the equator, the distribution of impact craters is relatively small.This diversity of geomorphic features and geological ageEnceladus(The moon is slightly smaller than Enceladus).The discovery of this young landform caused a great sensation in the scientific community - at that time, there was no theory that could explain why such a small celestial body (compared with the violentIo, it has been in a cooling state) there is still geological activity.However, the observation data of Voyager 2 cannot prove whether there is still geological activity on Enceladus at this stage, or whether the satellite is the source of the E-ring material.
Uncover the mystery of Saturn's atmospheric water vapor: triggered by Enceladus' jet hot springs
These mysteries lasted until July 1, 2004Cassini spacecraftIt was solved after entering the orbit around Saturn.Based on the observations of Voyager 2, Enceladus has become a priority observation target of the Cassini spacecraft program.Cassini has made several purposeful flybys within 1500 km and many non purposeful flybys within 100000 km, providing a large amount of observation data.so far,CassiniA total of four close range flybys were carried out, and a lot of significant information about the surface of Enceladus was obtainedsteamAnd complexhydrocarbonThese findings also prompted Cassini to change its flight trajectory and perform a closer flyover of Enceladus, including a close encounter in March 2008.In this encounter, Cassini carried out a detection of Enceladus with an accuracy of less than 52 kilometers.From 2008 to 2010, Cassini's follow-up missions included seven close flybys to Enceladus, of which two flybys in the second half of 2008 were nearly 50 kilometers away,
The discovery of Cassini on Enceladus has led to the follow-up of several research projects.In 2007,NASAA conceptual study of a plan to launch an orbiter to Enceladus and study plumes in Antarctica in detail has been completed. Unfortunately, the plan has not been further implemented.European Space AgencyIt is also planned to launch a probe to Enceladus, which will be implemented together with the research program of Titan.
The "Titan Saturn Plan" is a plan jointly proposed by NASA and the European Space Agency to explore the Satellites of the Saturn system (including Enceladus), and the competing plan is the "Europa Jupiter Plan".In February 2009, the National Aeronautics and Space Administration of the United States and the European Space Agency announced that they would give priority to the implementation of the Europa Jupiter program, while continuing to study the feasibility and timing of the Titan Saturn program.
The Cassini spacecraft, which was launched at the end of the twentieth century and arrived near Saturn at the beginning of the twenty-first century, provided a large amount of data and solved many doubts left by tourists after their visit.In 2005, Cassini spacecraft passed through Enceladus several times at close range and obtained a large amount of data on the surface of the satellite and its environment, especially found water rich plumes ejected from the Antarctic region of the satellite.This discovery, together with the presence of detectable escape internal energy and the rare occurrence of impact craters in the Antarctic region, proves that Enceladus still has geological activities. Many satellites in the satellite system of giant planets will become victims of orbital resonance, which will lead to star vibration and orbital disturbance,Tidal effects will heat the interior of the planet, which may explain the geological activities of Enceladus.
In 2017, the data sent back by Cassini showed that there were a large number of hydrogen molecules in the water vapor plume ejected from the ice layer on the surface of Enceladus. Researchers speculated that this was due to the hydrothermal reaction between the oceans of Enceladus and the rock core.If the speculation is correct, there may also be methane, an important chemical for life in the oceans of Enceladus.[1]
On October 7, 2022, it was reported that Hao Jihua, a researcher at the University of Science and Technology of China, and others recently found that the subglacial ocean of Enceladus may contain rich dissolved phosphate, which can support the origin and reproduction of potential microorganisms.This discovery fills the gap in the study of the habitability of the sea water of Enceladus, and provides scientific reference for the future exploration of possible life of Enceladus.[16]
In March 2024, a team of robotics experts from the Jet Propulsion Laboratory of California Institute of Technology, in cooperation with scientists from the Robotics Research Institute of Carnegie Mellon University, developed a snake shaped robot to investigate the terrain of Saturn's sixth largest satellite, Enceladus, in order to find clues to life.[20]
Satellite naming
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Enceladus（Enceladus）It was named after the giant Enceladus in Greek mythology.This name and six others were found in the first batchSaturnThe names of satellites areWilliam Herschel 's sonJohn Herschel It was first proposed in his Results of Astronomical Observations made at the Cape of Good Hope published in 1847.The reason for the name is that Saturn represents the god of agricultureSaturnusThat is, in Greek mythologyTitans Leaders ofCronos。
International Astronomical UnionWith Arabic literary works《The one thousand one night》The surface structure of Enceladus is named after the names of people and places in.The impact crater is named after people, and other geological structures such as deep valleys, ridges, plains and trenches are named after places.So far, the International Astronomical Union has officially named 57 geological structures, and another 22 geological structures discovered by Voyager in 1982 have also been named. In addition, the naming of 35 geological structures discovered by Cassini in its three flybys in 2005 has also been recognized in November 2006.These recognized names include Samarkand Trough, Aladdin Crater and Ceylon Plain.
Physical characteristics
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Size: 513.2 × 502.8 × 496.6 km
Average radius: 252.1 ± 0.1 km (0.0395 times the earth's radius)
Surface temperature (thermodynamic temperature scale): minimum average maximum 32.9 K75 K145 K
Star magnitude: 11.7
Atmospheric composition:
91% water vapor
4% nitrogen
3.2% CO2 1.7
%Methane
topographic features
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Comparison of the size of Enceladus and Britain
Enceladus is a relatively small satellite, with an average diameter of 505 kilometers, only one seventh the diameter of the moonBritainThe maximum length of the island is slightly smaller and its size is on par with that of Britain.andArizonaandColoradoIt can also accommodate this satellite.However, if the sphere area is much larger than these areas, its area is 800000 square kilometers, equivalent toMozambiqueOf land area, compared withTexasThe mass and diameter of the largest 15% of Enceladus rank sixth among Saturn's satellites, behind Titan (5150 km), Rhea (1530 km), Iapetus (1440 km), Rhea (1120 km) and Triton (1050 km).It is also one of the smallest spherical moons owned by Saturn. Except for Titan (390km), other small moons are irregular,
In fact, Enceladus is aFlat ellipsoidAccording to the photos sent back by Cassini, it is estimated that the three-axis length of Enceladus is 513 (a) × 503 (b) × 497 (c) kilometers, where (a) is the distance between the two poles facing Saturn and facing away from Saturn, (b) is the distance between the concave and convex poles of the star, and (c) is the distance between the south pole and the north pole.Enceladus rotates on its short axis, while its long axis diverges radially from Saturn.
surface
High resolution mosaic photos of the surface of Enceladus
In August 1981, Voyager 2 made the first close observation of Enceladus in human history.After analyzing the image information obtained, scientists found at least five different landforms, including impact crater terrain, flat terrain (relatively young), and near the flat terrain, ridges are often distributed. In addition, a large number of linear ground fissures and cliffs are also observed.Since there are few impact craters distributed in flat areas, scientists speculate that the formation time of these flat areas may only be several hundred million years.Therefore, in a relatively recent period of geological time, geological activities such as "water volcanoes" must have occurred on Enceladus, so that the original surface with many holes could be flat as before.Solid water (ice) has greatly changed the surface of Enceladus, making it the most reflective object in the solar systemGeometric albedoUp to 138%.Because it reflects so much sunlight, the night temperature of its flat surface is only - 198 ℃ (colder than other Saturn satellites).Cassini flew over Enceladus three times on February 17, March 9 and July 14, 2005, and observed more details of its surface.For example, the flat terrain observed by Voyager 2 is actually some areas where impact craters are less distributed. Such areas also have ridges and cliffs. At the same time, in areas with large geological ages and dense impact craters, a large number of ground fissures have been found, which proves that after the formation of a large number of impact craters,This area has also experienced intense geological movements. In addition, several younger landforms such as a strange terrain near the South Pole have also been found in the area that Voyager 2 did not survey in detail in the past.
The jet of water ice from Enceladus appears to have passed over Saturn's bright side.This photo was taken by NASA's Cassini spacecraft.In fact, Enceladus orbits about 112000 miles (180000 kilometers) from the top of Saturn's atmosphere.Enceladus' icy geysers were discovered in 2005. They are located in the fault zone of the planet's southern hemisphere. It is believed that the jet power of Enceladus is from the liquid water layer under the surface.
Impact crater
Damaged impact crater on Enceladus
Impact craters are a common phenomenon on many celestial bodies in the solar system.Many regions of Enceladus are covered by impact craters with different density and damage degree.Based on the observations of Voyager 2, scientists divided the crater into three types of crater topographic units according to the distribution density of the crater.Although ct1 and ct2 are different in the damage degree of impact craters, they both contain a large number of impact craters with a diameter of 10-20 km;While cp is a flat area with a few impact craters.This subdivision of crater topography based on crater density (and associated surface age) supports the view that Enceladus has experienced multiple stages of surface remodeling.The recent Cassini observations provide more detailed information about the ct2 and cp topographic units.These high-resolution images show that many of Enceladus's impact craters have been severely damaged by viscous collapse and structural cracks.Viscous collapse is the damage of the impact crater and other water ice terrain caused by gravity. This process requires a long geological time and will eventually flatten the terrain in this area.The effect of this action depends on the temperature of the ice, because the ice with higher temperature is more likely to be damaged than the ice with lower temperature and harder texture.The impact crater that has experienced viscous collapse generally has a convex bottom, and sometimes only a circle of crater edge remains.The convex bottom of the Dunyazad crater, the large impact crater at the upper left corner of Figure 8, is an example of viscous collapse.In addition, many impact craters on the surface of Enceladus have been severely damaged by structural cracks.The impact crater with a diameter of nearly 10 kilometers at the bottom center right of the photo is proof that the elongated crack with a width of only a few hundred meters to one thousand meters has seriously damaged the edge and bottom of the impact crater.So far, almost all the impact craters located in the ct2 topographic unit have signs of tectonic deformation. The role of viscous collapse and structural cracks has proved that although the impact crater terrain area is the area with the largest geological age and the highest retention of impact craters on Enceladus, almost all the impact craters in it are in a certain stage of destruction.
geological structure
Voyager 2 discovered several geological structures on Enceladus, including grooves, cliffs and ridges.Recent observations by Cassini show that the main way to change landforms on Enceladus is tectonism.A more interesting geological structure found on Enceladus is the rift. These canyons can extend to 200 kilometers long, 5-10 kilometers wide and 1 kilometer deep.Figure 7 shows the scene of a typical large rift cutting those areas with older geological age and structural damage.This geological structure is also shown at the bottom of Figure 8.The crack is a younger geological structure, because it usually cuts other geological structures, and there are prominent outcrops on both sides of the crack.
Another example of tectonism on Enceladus is the trench structure, which consists of a series of curved trenches and ridges.This stripe structure was first discovered by Voyager 2, which is usually the dividing mark between flat terrain and impact crater terrain.This geological structure can be seen in Figure 6 and Figure 10 (Samarkand trench in Figure 10).This kind of trench terrain is easily reminiscent of similar landforms on Ganymede.However, the trench structure of Enceladus is more complex than that of the latter: the trench on Ganymede is arranged in parallel, while the trench arrangement of Enceladus is messy, and its shape is mostly zigzag.It is interesting that Cassini found some dark spots (125-750 meters in diameter) when observing the Samarkand trench, which are parallel to the trench. It is speculated that these dark spots are the pits in this area.
In addition, there are many geological structures on the surface of Enceladus.Figure 9 shows a narrow fault terrain (usually hundreds of meters wide), which was discovered by Cassini.These cracks often penetrate the impact crater terrain, and their depth is only one or two hundred meters.Many of the cracks were affected by the thin topsoil produced by the impact crater during their formation, resulting in frequent changes in the crack strike.
flat terrain
Voyager 2 discovered two flat terrains on the surface of Enceladus.The relief of these terrains is relatively small, and the number of impact pits is also small compared with the impact crater terrains, which indicates that this geological structure was formed later.The typical one, Ceylon Plain, has no visible impact crater.Another flat terrain in the southwest of Ceylon Plain is crisscrossed with several grooves and cliffs.Since then, Cassini has also observed these flat terrain, including Ceylon Plain and Tiya Plain, and took high-resolution photos.These photos show that the terrain is actually full of lower ridges and shallow cracks.At present, it is believed that the cracks are caused by shear deformation.The photos taken in the Ceylon Plain show that there are still a certain number of small impact craters in this area. According to the estimation of these impact craters, the surface age of this area varies from 170 million years to 3.7 billion years, depending on the distribution of impact craters.
The expansion of the area observed by Cassini on the surface of Enceladus has made it possible to find more flat terrain, especially on the sphere of Enceladus moving towards the orbit.These landforms are covered with a large number of grooves and ridges, similar to the deformation structure in the Antarctic region.These terrains are located on the opposite sides of the spheres of Ceylon Plain and Tia Plain, indicating that the region is affected by Saturn's gravitational tides.
Antarctic region
On July 14, 2005, scientists found a special area of tectonic deformation in the Antarctic region in the photos taken by Cassini when it flew over Enceladus.This area is located at 60 ° north latitude, with cracks and ridges all over it. At the same time, there are a few micro impact craters, which indicates that this is the youngest landforms on the surface of Enceladus, and also the youngest landforms on all medium-sized frozen satellites;The impact crater structure between them indicates that some areas of the region may be only 50000 years old, or even younger.The central area near the area is distributed with four fracture zones and many ridges, which are informally named“Tiger Stripes ”。These cracks may be the youngest geological structure in the region, and they are surrounded by peppermint green ice bodies with rough texture - these ice bodies often appear in rock outcrops or crack walls in other regions."Blue" ice is also found in the flat area of the area, which indicates that the area is so young that it has not yet been covered with a layer of fine textured ice from the E-ring.The detection results of the visible light and infrared mapping spectrometer (VIMS) show that the chemical structure of the green material distributed around the "tiger skin stripe" is different from other surface materials of Enceladus. At the same time, transparent ice bodies are found in the "tiger skin stripe", which indicates that this geological structure is very young (probably less than 1000 years),Or the ice body on the surface of the geological structure was recently affected by heat sources.In addition, the instrument also measured the simple structure ofOrganic compoundThis is the first discovery on the satellite.
During the flyby on July 14, Cassini observed one of the "blue" ice distribution areas in the Antarctic region and took high-resolution photos, which showed that there was severe geological deformation in the area, and found some boulders with a diameter of 10-100 meters.
Enceladus' Antarctic region is surrounded by a series of parallel ridges and canyons in Y and V shapes.The shape, trend and position of these ridges and canyons all indicate that they are caused by the overall deformation of Enceladus.Recently, there are two theories to explain the formation of this topographic deformation.The first is that the orbit of Enceladus around Saturn has shrunk, leading to the increase of the rotation speed of Enceladus, which in turn leads to the adjustment of the rotation axis of Enceladus.The second theory holds that a large amount of warm, low-density material ejected from the interior of Enceladus causes the region where this terrain is located to move from the mid latitude region of the southern hemisphere of Enceladus to the high latitude region.As a result, the ellipsoid of Enceladus will be adjusted accordingly due to this change.One of the results derived from the theory of rotation axis change is that there have been similar topographic changes in the northern and southern poles of Enceladus.However, contrary to the inference, the Arctic region of Enceladus is densely covered with impact craters, and its geological age is much larger than that of the Antarctic region.The uneven thickness of Enceladus' crust may explain this difference.This change in crustal thickness is supported by the correlation between the Y-shaped and V-shaped landforms on the edge of the Antarctic region and the geological age of the region adjacent to the Antarctic: the Y-shaped and discontinuous landforms and the north-south fault zones are all younger landforms, and it is speculated that the crustal thickness corresponding to this terrain is thinner;The V-shaped terrain is adjacent to those areas with older geological age and dense distribution of impact pits.
Ice volcano
A Possible Model of Enceladus Ice Volcanoes
After the Voyager spacecraft observed Enceladus in the early 1980s, scientists believed that there might be geological activity in the star based on the following reasons: the young, highly reflective surface and its position in the core area of the E-ring.The connection between Enceladus and the E ring makes scientists suspect that Enceladus is the source of the substances scattered on the E ring - that is, the water vapor ejected from the inside of Enceladus finally forms the E ring.However, Voyager's observations failed to provide conclusive evidence that Enceladus is still active today.However, Cassini later carried a variety of instruments. Through the observation of these instruments, scientists finally found that there was eruptive water and other volatile substances on Enceladus, rather thansilicateAn ice volcano of rocks.In January and February 2005, the imaging science subsystem (ISS) on Cassini observed for the first time the plumes composed of tiny ice crystals that erupted from the Antarctic region of Enceladus.During the flyby on February 17, 2005, the magnetometer observed data about the atmosphere of Enceladus, which also proved that the phenomenon observed by the imaging science subsystem before was true - the data showed that the energy of ion cyclotron waves near Enceladus was enhanced at that time.Ion cyclotron waves are ions andmagnetic fieldThe composition of the substance can be determined by measuring the frequency of the ion cyclotron wave of the product of interaction - after measurement, this substance is ionizedsteam。In the two subsequent flybys, the magnetometer found that most of the gases in the atmosphere of Enceladus were concentrated in the Antarctic region, while the atmospheric concentrations in other regions were relatively thin.During the flyover on February 17 and July 14, two cases were observed by the ultraviolet spectrograph (UVIS)OccultationPhenomenon.During the February flyover, the ultraviolet spectrograph failed to find evidence of the existence of atmosphere in the equatorial region of Enceladus, but the presence of water vapor was detected during the July flyover observation of occultation.
Cassini accidentally passed through the gas cloud, the ion and neutral particle spectrometer (INMS) and the cosmic dust analyzer (CDA), so that it can directly obtain samples of plumes.The ion and neutral particle spectrometer measured the material composition of the gas cloud, and found that most of them were water vapor, and contained a small amount ofMolecular nitrogen, methane and carbon dioxide.The cosmic dust analyzer found that "the closer to Enceladus, the more particulate matter", which proved that Enceladus was indeed the main source of E-ring matter.The data from the ion and neutral particle spectrometer and the cosmic dust analyzer show that the gas cloud that Cassini passed through is indeed a water rich plume from an ice volcano, which originates from an Antarctic jet.
In November 2005, this ejection activity was further confirmed. The imaging science subsystem photographed the ice crystal ejection activity similar to a fountain in the Antarctic region of Enceladus.(In fact, Cassini had already taken plumes in February 2005, but it is still necessary to further study the photos taken from a high phase angle - that is, the photos taken when the sun is behind Enceladus - to truly confirm their existence. These photos need to be compared with the high phase photos of other Saturn satellites.)The observation results in November showed the complete structure of the plume, and found that the plume was composed of several independent ejections (perhaps from several different ejectors), and extended to an area nearly 500 kilometers from the surface of the satellite.This observation makes Enceladus the fourth solar system object confirmed to have volcanic activity. The previous three are EarthTriton andIo。In October 2007, while the imaging science subsystem observed the dust jet activity, the ultraviolet spectrograph also observed the gas jet activity.
The flyby on March 12, 2008 gave Cassini further observation opportunities.Observational data show that plumes contain more chemicals, including simple and complexhydrocarbon, such aspropane、ethaneandacetylene。The discovery raises the possibility of life on the surface of Enceladus.The ion and neutral particle spectrometer on Cassini measured the material composition of the plume and found that it was similar to that of most comets.The observation results of various observation instruments show that in the Antarctic region of Enceladus, this activity of erupting plumes from the pressurized basement is similar to the fountain on Earth.Since ion and neutral particle spectrometers and ultraviolet spectrographs are not found in the ejected materialammonia——This substance can prevent freezing. Therefore, scientists predict that near pure liquid water with a temperature of at least minus 3 degrees Celsius flows in the heated and pressurized chamber under Enceladus, as shown in Figure 13.The melting of ice into pure water requires more heat than the melting of ammonia water mixture.This heat may come from gravitational tidal energy or energy generated by radiation sources.Another way to produce plumes is the sublimation of the warm ice on the surface of Enceladus.During the flyby on July 14, 2005, the infrared component spectrometer (CIRS) on Cassini found a warm area near the South Pole. The temperature of this area reached 85-90 Kelvin, and the temperature of some areas even reached 157 Kelvin (minus 116 ℃), which is far higher than the temperature generated by the surface receiving solar radiation,This indicates that the region is heated by the internal heat source of Enceladus.At this temperature, the ice body in this area can sublimate much faster than the ice body in other areas, and produce plumes.This hypothesis has attracted more attention because if the underground material that heats the surface ice body is a mixture of ammonia and water in a semi fluid state, it does not need too much energy to produce plumes. However, a large number of ice crystals rich in plumes obviously support the "cold fountain" model hypothesis and weaken the credibility of the ice body sublimation hypothesis,
In addition, Kiev et alclathrate hydrate According to the source theory, when the "tiger skin stripe" terrain breaks, the carbon dioxide, methane and nitrogen contained in it are exposed tovacuumTo be released.This theory does not need the existence of heat energy for ice melting in the "cold fountain" model hypothesis, and can also be explained in the absence of ammonia.
internal structure
Construct the internal structure of Enceladus based on Cassini observation results
Before the Cassini plan, little was known about the internal structure of Enceladus.However, the detection results obtained during several flybys of Cassini spacecraft to Enceladus provide necessary information for building the internal model of Enceladus, including the determination of the mass and triaxial ellipsoid shape of Enceladus, high-resolution surface photos and new discoveries in geochemistry.Previous mass measurements of Enceladus by travellers suggest that it may be entirely composed of solid ice.However, according to the measurement of the gravity effect of Enceladus on Cassini, this value is much higher than previously speculated, and its density reaches 1.16g/cm3, higher than other medium-sized SaturnIce satelliteWhich indicates that Enceladus may contain moresilicateandiron。The presence of substances other than solid ice means that the interior of Enceladus may haveRadioactive materialThe relatively abundant heat energy generated by decay.
Castillo and others believe that Iapetus and other Saturn's icy moons were formed shortly after the formation of Saturn's sub nebula, so they are rich in short-term radionuclides.These radionuclides, such asAl-26andIron - 60, there are shorterhalf lifeAnd can provide heat energy for the core of stars relatively quickly.Although Enceladus has relatively high density rock structure, without these short-term radionuclides, the long-term radionuclides inside Enceladus will not have time to prevent the rapid freezing of the core.In view of the high-density rock structure of Enceladus, it is speculated that the high content of Al-26 and Fe-60 will lead to the emergence of a different structural type, which includes a frozenmantleAnd a rock core.Later, the radiation energy and tidal action raised the temperature of the core to 1000K, which is enough to melt the inner mantle.However, if we want to maintain the active geological activities of Enceladus, part of its core must also be melted to formMagmaCavities, which are distorted by Saturn's tides.EnceladusOfResonance effectorLibrationThe tidal heat generated makes these hot spots in the core still active, and provides energy for the geological activities on Enceladus,
In addition, scientists also measured the shape of Enceladus to further determine whether the satellite has an internal layered structure.Polk et al. believed that the star is located in theHydrostaticsIn this state, the interior of the star is not stratified, which contradicts the results pointed out by geological and geochemical evidence.However, the shape of the star does not rule out the possibility that it is not in hydrostatic equilibrium. It is possible that Enceladus may still have a layered internal structure in a relatively recent period, and the rotation speed in some regions of the star is faster than that in other regions,
Underground heat source
Therefore, scientists have studied the hypothesis that there is a continuous heat source underground Enceladus.At the meeting, relevant experts put forward their own views: the decay of radioactive materials inside Enceladus is a continuous source of heat energy.
Dennis Mattson, one of the main researchers of NASA's Cassini project, said that at the beginning of the formation of Enceladus, it was a mixture of ice and rock, in which the rock part contained two radioactive isotopes.Over the past 4.5 billion years, the radioactive decay has continued, emitting a large amount of heat energy, gradually creating the structure of Enceladus' rocky core surrounded by ice.Until today, the radioactive decay inside Enceladus has not stopped, and the heat generated by the core has further melted the central part of Enceladus,
It is this repeated radioactive decay that has provided a steady stream of heat energy for Enceladus, and has broken the balance of the ice near its South Pole, forming a high-temperature region, resulting in ice fracture, which directly led to the eruption of ice debris and water vapor captured by Cassini.
Surface temperature
There is no rain on Enceladus, but there are geysers on its surface, from which a large amount of water vapor is ejected. This process is called a cryovolcanism.People have different opinions about the exact composition of this satellite and its plume extending from its surface.Some people believe that the liquid surface of the satellite is covered with a layer of ice, while others believe that it is a cold celestial body composed of solid ice and rock.
Underground sea
European and American astronomers recently reported in Science that they judged that Saturn's moon Enceladus has a huge "underwater sea" by analyzing the gravitational field.This may be one of the ideal places to look for extraterrestrial life[3]。
Enceladus is a "small world" with a diameter of only about 500 kilometers, and its surface is surrounded by dazzling white ice.In 2005, the Cassini probe found that there are some parallel banded landforms called "tiger stripes" distributed in the south pole of Enceladus, and ice debris geysers erupted. Therefore, scientists suspect that Enceladus may have an "underground sea".
Astronomers analyzed and determined the gravitational field of Enceladus using the data obtained from three close observations of Enceladus by the Cassini probe from 2010 to 2012.It is found that the gravitational field of Enceladus has a "striking asymmetry". The gravity of Antarctica is weak, but it is larger than the value calculated according to its topography.They believe that the "compensating effect" is the liquid water under the surface of the Antarctic, because the density of water is greater than ice, and the gravity formed is also greater than ice.
Further analysis shows that the "underground sea" is located under the surface ice layer 30 to 40 kilometers thick at the south pole of Enceladus, which is about 10 kilometers thick and extends to about 50 degrees south latitude.David Stevenson, a professor at the California Institute of Technology who participated in the research, said: "This means that its area is equal to or even larger than Lake Superior, the second largest lake on the earth."
The research also shows that the bottom of the "underground sea" of Enceladus may be silicate rocks, which means that the environment here is suitable for complex chemical reactions, including those that may have created a similar early Earth environment.
In addition, scientists believe that Jupiter's moon Europa, which is similar to Enceladus, may also exist "underground sea".Stevenson said that studying the two satellites will help to understand the livable environment in the solar system.There must be other planets with abundant water resources in the solar system.
Orbital period: 1.370218 Earth days or 118386.82 seconds
Orbit inclination: 0.019 ° (relative to Saturn's equator)
Planet of satellite: Saturn
Enceladus orbits Saturn in an orbit 238000 kilometers away from the center of Saturn and 180000 kilometers away from the top of its cloud layer. Its orbit is located in the inner satellite of Saturn, which belongs to Enceladus.Enceladus ranks 14th in terms of distance from Saturn, and its orbit is located in the dense part of Saturn's E ring
Orbital map of Enceladus from Saturn's North Pole
The revolution period with Triton is 32.9 hours (its displacement can be found through one night's observation).Its orbit forms a 2:1 orbital resonance with that of Rhea, that is, whenever it completes two revolutions, Rhea completes one revolution.This orbital resonance relationship leads to the eccentricity of Enceladus orbit reaching 0.0047 and provides a heating source for its geological activities.
Like most of Saturn's big moons, the rotation of Enceladus is synchronized with the revolution, and it always faces Saturn on the same side.Unlike Enceladus, the moon has no swing of its rotation axis (while the moon has a swing of more than 1.5 °).However, the analysis of the shape of Enceladus shows that sometimes it will produce the disturbance of its rotation orbit due to external forces, such as the orbital resonance effect of Enceladus.Such disturbances can also provide additional heating sources for Enceladus.
Interaction with E-ring
This figure shows the relationship between Enceladus and Saturn's E ring
E ring is the outermost ring of Saturn. It is extremely wide (the widest ring in Saturn's rings), but also extremely thin. The composition material is only very small ice crystals and dust. The ring starts from the orbit of Titan and extends to the orbit of Rhea. Some observers even think that it has extended to the orbit of Titan. If so, its width will reach 1 million kilometers.However, many mathematical formulas show that such a ring is unstable and can only last for 10000 to 1 million years. From this point of view, the particles constituting the ring must be continuously supplemented from somewhere, while the orbit of Enceladus is just in the ring and in the densest part of the ring.Therefore, some theories speculate that Enceladus is the source of the particles forming the E-ring.The Cassini observations support this view.In fact, there are two different mechanisms for Enceladus to supplement the particles in Saturn's E ring.First, and most importantly, it is the plumes ejected from the Antarctic region of Enceladus. Although most of the ejections fall back to the surface of the satellite, because the escape speed of Enceladus is only 866 km/h, some materials still escape from the gravity control of Enceladus and enter the orbit around Saturn.The second mechanism is that the meteor bombards Enceladus, causing the dust on its surface to enter the annulus.This mechanism is not unique to Enceladus. It is effective for all satellites in the E-ring,
Enceladus operates in Saturn's E ring
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The night sky above Enceladus
Seen from Enceladus, Saturn occupies nearly 30 °visual angle, which is more than 60 times larger than the view angle of the moon observed from the earth.In addition, due to the synchronous rotation and revolution of Enceladus, Enceladus always faces Saturn from the same side, so Saturn never moves in the night sky of Enceladus (except for minor changes caused by orbital anomalies), while Saturn will never be seen on the side of Enceladus opposite Saturn.
Artistic Imagination of the Night Sky of Enceladus
The observable angle of Saturn's ring is only 0.019 °, which looks like a bright thin line across Saturn's disk, but the shadow it falls on Saturn's disk can be clearly recognized.Just like the moon observed on the earth, Saturn observed on Enceladus also has regular phase changes, which takes a 16 hour period from loss to win.At the same time, the sun only occupies a 3.5 'view angle, which is 9 times smaller than the view angle of the moon observed from the earth. If an observer observes on Enceladus, he can observe every 72 hours on averageEnceladus(The largest satellite inside the orbit of Enceladus) moves in front of Saturn.The view angle of Mimas is close to the moon, and the maximum is 26 ';andTelestoandEnceladus 32The size is like a star;EnceladusThe maximum angle of view can be slightly more than 1 °, twice the angle of view of the moon, but it can only be seen from the back of Enceladus to Saturn when it is closest to Enceladus.[4]
Enceladus space "fountain"
Enceladus Fountain Imagination
In March 2008, the US Cassini probe flying near Enceladus sent back photos showing that there were ice debris and water vapor eruptions similar to geysers on Enceladus, indicating that liquid water may exist on this celestial body.Although there is no liquid water in the picture, scientists believe that the ice debris and water vapor in the picture come from the "underground reservoir" at the shallow surface of Enceladus.
The researchers suspect that the liquid water surface is covered with thin ice.If cracks appear in the covered ice layer, the temperature and pressure of liquid water will drop sharply. On the one hand, water vapor will erupt, and on the other hand, the ejected water vapor will quickly condense into ice chips, similar to the hot springs on the earth, but the temperature is much lower.
Caroline Polk, an image analysis expert at the Colorado Institute of Space Sciences, said that if there is liquid water on the planet whose surface temperature is as low as minus 200 degrees Celsius, there may be heat sources underground.In addition, researchers from the University of Arizona in the United States believed that there might be a small amount of organic matter near the south pole of Enceladus through spectral analysis of the data returned from Cassini.
Geyser section under the ice layer of Enceladus
Recently, NASA's Cassini probe has made new discoveries,[5]According to the latest news, Cassini has found as many as 101 geyser vents under the ice layer of Enceladus, which means that Saturn, the "ice satellite", has more ice water composition, and there is a special heating mechanism underground, which can melt the ice layer.The figure shows the cross-section of the geyser below the ice layer of Enceladus, which can clearly see three layered structures. The bottom is the conduction heat source. The generated heat heats the ice layer, and the formed steam and brine droplets are located in the second layer and rush out from the weak position on the surface.
Scientists' research on Enceladus has found that there may be a large amount of liquid water below its surface. In the past seven years, the Cassini probe has begun to scan the south pole of Enceladus through a high-resolution camera system. Its unique geology has left a deep impression on scientists. Here are cracks that look like tiger stripes, in which tiny ice particles are also ejected,After all the scans, scientists confirmed the location of 101 geysers and mapped out the distribution map of the geysers of Enceladus. At the same time, NASA researchers also found that there are surface heat sources around several geysers, which may be related to deeper internal heat sources.
The discovery of the geyser of Enceladus dates back to 2005. Scientists speculate that the tidal force of Saturn caused the heat source in the interior of Enceladus, which erupted at a thin position on the surface, resulting in the formation of a geyser with tiny ice particles.Prior to this study, researchers did not know which role played a dominant role in this process, nor were they sure whether the excess energy inside Enceladus could affect the near surface area.
In order to determine the location of geysers, scientists used the triangulation method used in geological survey to draw the relationship map between the thermal radiation source of Enceladus and the location of geysers. It can be seen that the geysers erupted more violently in areas with greater thermal radiation, which indicates thatThe geyser eruption on Enceladus is not a near surface phenomenon, but related to deeper heat sources,And a large part of these heat sources come from the tidal force of Saturn.From this, scientists can conclude that a huge ocean under the ice can be formed between the heat source and the surface ice layer, which reaches the surface through narrow channels.
According to the high-resolution camera system of Cassini detector, scientists observed the periodic geyser eruption in the polar region of Enceladus, which is well matched with the tidal force model of Saturn, further proving the relationship between the internal heat source, tidal force and geysers of Enceladus.
NASA's Cassini probe sent back images of the jet stream of Enceladus. The Cassini probe even collected some substances in the jet stream of Enceladus, measured the jet stream through the ultraviolet imaging spectrometer (UVIS), and scientists obtained the data of gas content in the jet stream.The latest detection found that the jet stream contained ice particles, water vapor and organic compounds.[6]
Vital signs
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Enceladus
Scientists have made a major breakthrough in the field of extraterrestrial life exploration!The Nasa Cassini probe provides scientists with clear evidence of the current hydrothermal activity of Enceladus for the first time, and it is likely that the subsurface ocean of this satellite has conditions for breeding life.
If this discovery is confirmed, Enceladus will become the only planet in the solar system other than the Earth that has hot water and underground interaction. Hydrothermal activity makes Enceladus a satellite of potential microorganisms.Scientists have found some strange life on the earth that can live in hydrothermal vents at the bottom of the sea without sunlight.
NASA pointed out that such hydrothermal activity on planets beyond the Earth will open up unprecedented scientific possibilities.This discovery implies that the underground ocean of Enceladus and its unique geological activity are potentially suitable for the survival of organisms.It is reported that the scientists' survey results show that the underground ocean of Enceladus is deeper than previously thought, and is 48 kilometers below the surface of the satellite.
The location of Enceladus in the solar system and its extreme environment may have life, which may reveal a mystery: Is the earth human unique in the universe?
Hydrothermal activity occurs in the process of seawater infiltrating rock crust and reacting, and usually occurs in heated, mineral bearing liquids in the earth's oceans.The study was published this week in the journal Nature.
During the 4-year space probe data analysis, computer simulation and laboratory experiments, researchers have come to a conclusion that a tiny particle of Enceladus is likely to form in the process of contact between hot water containing dissolved minerals and cold water.The interaction of tiny particles requires a temperature of at least 90 degrees Celsius. Sean Xu, a postdoctoral graduate student at the University of Colorado, Boulder, pointed out that what excites us is that these tiny rock particles are ejected into space through geysers, which can help us grasp important information about the state of the Titan's seabed.[7]
Cassini will fly close to Enceladus again: or find evidence of life
On October 27, 2015, Beijing time, NASA's Cassini space probe will pass through one of the largest ice plumes on the surface of Enceladus. Scientists hope to learn more about the ocean under the ice shell of Enceladus.
The instruments on board Cassini will collect samples of the jet and analyze its chemical composition.Previously, Cassini had also passed through the ice plume from the surface of Enceladus, but this mission will be the closest one to the surface of Enceladus.At a lower altitude, Cassini will be able to detect heavier molecules, including organic substances that can prove the existence of life.
Astronomers believe that the material ejected from Enceladus originates from the liquid water ocean below its surface.This week, we will further explore Enceladus beneath the ice.
NASA's Cassini space probe will fly over Enceladus again at the end of October. This is a historic moment, which will solve the mystery hidden under the scarred appearance of Enceladus.
In this mission, the Cassini probe will fly only 30 miles away from the surface of Enceladus (about 48 kilometers) and make the latest "intimate contact" with the plumes ejected from the surface of Enceladus.
Since Cassini began to explore Saturn and its moons in 2004, the pictures and data sent back by Cassini show that the surface of Enceladus is full of cracks and craters.Enceladus is only 310 miles in diameter, and its surface is covered with a thick layer of ice. Below the ice is a sea of liquid water.
Scientists recently pointed out that the movement of the core of Enceladus may generate enough heat to keep the water under the crust liquid.Therefore, Enceladus is considered by scientists to be one of the planets in the solar system most likely to produce extraterrestrial life.
On Wednesday, the Cassini probe will pass through an ice plume.The ice plume is located in the Antarctic region of Enceladus. Scientists believe that it originated from the ocean under the ice crust and erupted through the crust.
NASADr. Curt Niebur, a scientist involved in the Cassini project, said: "In the past decade, Cassini has made many important discoveries."
"For NASA and other partners involved in the Cassini project, the ice plume passing through the surface of Enceladus will be an excellent opportunity. At that time, we will be able to answer the question: 'Will there be essential elements of life in such an icebound ocean world?'"
During this mission, the instruments on board the Cassini will collect samples of the jet and analyze its chemical composition.
Previously, Cassini had also passed through the ice plume from the surface of Enceladus, but this mission will be the closest one to the surface of Enceladus.At a lower altitude, Cassini will be able to detect heavier molecules, including organic substances that can prove the existence of life.
Scientists also hope that Cassini can take this opportunity to detect how much hydrothermal activity exists on the surface of Enceladus, and how these heat flows affect the habitability of Enceladus.
Dr. Hunter Waite of the Southwest Research Institute, the leader of the ion and neutron mass spectrometer team on Cassini, said: "If we can confirm that the ice plume of Enceladus contains hydrogen molecules, we can find another evidence that there is hydrothermal activity on the seabed of Enceladus."
"The amount of hydrogen can reflect the scale of hydrothermal activity on Enceladus."
Cassini will fly over Enceladus for the last time on December 19 this year, and calculate how much heat is emitted from the interior of Enceladus. The flight altitude will be 3106 miles (4998 kilometers).
When the probe was closest to Enceladus, it was only 16 miles from its surface, but when it flew over the ice plume, its altitude was much higher than that of the mission, so most of the ejecta had dissipated.
In the task to be carried out this week, scientists will be given a valuable opportunity to conduct detailed detection of the chemical substances contained in the ice spring.
The source of these ice plumes is the intermittence on the surface of EnceladusIce springThey spew 250 kilograms of water vapor, ice particles and volatile chemicals into the air every hour at a speed of 1360 miles per hour (2188 kilometers per hour).
The scientists compared these geysers with hydrothermal vents on the earth - there are some volcanic cracks on the earth's seabed, and the water temperature will become very high when seawater seeps into these cracks.In the coldest and deepest corner of the ocean, the complex chemicals around the hydrothermal vents provide an oasis for a large number of living things.
Scientists hope that by using theuniverseThis flyby mission will enable us to better understand the chemical composition of Enceladus' ice plumes.[8]
In order to try to find microbes that may exist in Europa's underground sea, the Cassini probe dived into the plume composed of water, ice crystals and organic matter released from the surface of Enceladus. An independent study pointed out that Europa has an area, which may be an ideal place for future space missions to search for extraterrestrial life.
When Cassini probe flew over the surface of Enceladus at 30600 km/h, it collected a drop of water. Scientists said that this drop of water was enough to answer some key questions about Enceladus, but it may take several months to analyze and verify the data before making any conclusions.
Curt Niebur, a Cassini mission scientist, said: "This is an important step in exploring the new era of the ocean world in the solar system, and Europa and Enceladus are likely to become potential oases of extraterrestrial life." It is reported that Cassini does not have instruments and equipment to directly detect life, but scientists hope to find detailed information about the underground ocean,The subsurface ocean is believed to be the source of the Enceladus geyser plume.Scientists speculate that tidal gravity keeps the underground ocean liquid.[9]
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Liquid water
In 2008, scientists observed water vapor ejecting from the surface of Enceladus.This observation proves the existence of liquid water on the satellite, and supports the view that there may be life on Enceladus.
Candace Hansen isNASACalifornia basedJet Propulsion LaboratoryA scientist of, led a team to study these substances after discovering these plumes with a speed up to 2189 km/h, which is very rare and can only be achieved with water.
The Cassini data show that there may be a global ocean beneath the frozen surface of Enceladus.After analyzing the ice crystal particles captured by Cassini, it was found that these ice crystal particles were agglomerated by salt water - a condition that generally only occurs in large areas of water.Therefore, extraterrestrial life may also exist on Enceladus.Another view is that what exists on Enceladus is not a large area of ocean, but a wide distribution of caves, which are full of liquid water.
On August 13, 2009, scientists released the latest results of the analysis of water vapor ejected from the Antarctic region of Enceladus. They found high concentrations of salt in ice crystal particles.In addition, Cassini also found traces of organic compounds such as carbonate and dust particles.These evidences strongly prove that there is an ocean under the surface of the satellite.The dust particles may even provide details about the ocean, which usually requires deep drilling.
The existence of liquid water under the crust of Enceladus indicates that there is an internal heat source in its interior.Now, scientists believe that radioactive decay and tidal effects together provide the heat needed for the existence of liquid water, because tidal effects alone cannot provide so much heat - for example, another moon of Saturn, Iapetus, is closer to Saturn than Enceladus, and its orbit eccentricity is greater, which means that compared with Enceladus,The satellite has been affected by more powerful tidal effects, but its old and traumatized surface indicates that the satellite seems to have stopped geological activities for a long time.
Existence life
Enceladus is one of the three stars in the outer solar system where geological eruptions have been observed so far (the other two areIoandTriton ）。The analysis shows that the ejected material is liquid water below the surface of the star;At the same time, strange chemical components are also found in the ejected plumes, so Enceladus is also considered asAstrobiologyImportant research objects.In addition, the ejection phenomenon also provides important evidence for the view that the material of the E-ring comes from Enceladus.[10]
Enceladus
The Associated Press said that this hypothesis is of great significance.If confirmed, Enceladus will have three major conditions to produce life: continuous heat source, organic matter and liquid water.Mattson said, "This tells us that with the internal conditions of Enceladus, it has or may still have biochemical reactions."
Of course, all hypotheses are only reasonable guesses after all.It is too early to say whether life exists on Enceladus.In March 2008, Cassini will fly again to observe only 350 kilometers away from Enceladus.At that time, more space mysteries may be revealed one by one.Enceladus may be the source of material in Saturn's thin E ring.In addition, because this material cannot exist in the halo for thousands of years, it may be related to the recent activity of Enceladus.In addition, the halo may also be maintained by high-speed particles constantly colliding with different satellites.
According to New Scientist magazine, American Princeton physicist and futurist Freeman Dyson said that there might be such a life of flowering plants on the cold moon Enceladus, because flowering plants are found in the Arctic region of the earth, and the environment of the Arctic and Europa is very similar, so spacecraft should look for flowers on Europa, which is easy to find.
On March 12, 2015, Japanese media reported that the University of Tokyo, the Japanese Ocean Research and Development Agency and other international teams in Europe and the United States had found a hot water environment on Saturn's second satellite, Enceladus.It is said that this is the first time that human beings have found an environment for life outside the Earth in the solar system.The results have been published in the British scientific journal Nature.[11]
Mystery to be solved
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The latest observation data from NASA's Cassini probe show that there are periodic hot bubbles of melting ice on the surface of Enceladus, and the ice shell on the surface of Enceladus is stirred.This will explain the peculiar thermal reaction phenomenon and surface characteristics on the surface of Enceladus.
Francis Nimmo, a planetary scientist at California State University Santa Cruz in the United States, said, "Cassini has observed Enceladus in a burping state, and it is very rare to see the turbulent period on the surface of Enceladus. It is likely that this satellite is in a special geological era."
The reason why the Antarctic region of Enceladus is of great interest to scientists is that it has a "tiger stripe" structure, which is formed by the diffusion of water vapor spray and other particles from the star.A new research report released on January 10 shows that the agitation and geological flattening of the ice crust on the satellite surface are not directly related to cracks and ejected materials, and these phenomena can be used to explain the gaps in the past geological history of Enceladus.
Bob Pappalardo, a Cassini project scientist at NASA's Jet Propulsion Laboratory, said: "The strange geological phenomena observed at present will help reveal the mysterious veil of Enceladus and explain the following mysteries - why is the South Pole of Enceladus so young? How does the South Pole of Enceladus eject a lot of heat?"
Cassini has observed that Enceladus is in a state of turmoil
About four years ago, Cassini detector synthetic infrared spectrometer detected that the heat flowing in the Antarctic region of Enceladus reached at least 1 billion watts, which is equivalent to the energy supplied by at least 12 power stations.Although the mass of Enceladus is smaller than that of the earth, its geothermal resources are three times the average value of geothermal resources generated in the terrestrial geothermal areas. After that, the ion and neutron mass spectrometer of Cassini detector found these geothermal resource areas by excluding argon, and these geothermal resource areas showed the radioactive attenuation of rocks,
Scientists have simulated that it is impossible for Enceladus to generate heat and gas at a certain rate continuously, and the tidal motion from Saturn's traction force cannot explain the release of so much energy.
At the same time, scientists found that the surface geological ages of different regions of Enceladus are very different. The history of craters in the northern hemisphere can be traced back to 4.2 billion years ago. The history of the "Sarandib Planitia" region near the equator can be traced back to 17 to 3.7 billion years ago, while the history of the southern hemisphere is less than 100 million years ago, and even some regions were formed only 500000 years ago.
Craig O'Neill and Nemo of Macquarie University in Australia are the founders of NASA's Outer Planet Research Program. They designed a computer simulation that can be used to analyze the convection conditions in the earth's crust.The analysis of this model applied to Enceladus shows that the icy layer completely covered on the surface of Enceladus is broken by the gravitational tidal traction of Saturn. They believe that the hardness of the surface of Enceladus is between the Earth and Venus.[12]
Latest findings
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Enceladus has the necessary conditions to support life
The National Aeronautics and Space Administration (NASA) held a press conference in the early morning of the 14th Beijing time, announcing the peak discovery of the Cassini probe: Saturn's sixth largest satellite, Enceladus, has oceans on it, which may support the survival of life.At the same time, Europa, Jupiter's fourth largest moon, has the same potential.These findings make us closer to answering the question of whether human beings are really "lonely".When the Saturn probe Cassini closely observed the Antarctic region of Enceladus in 2015, it was found that the plumed ice was ejected into space, containing a large number of hydrogen molecules and carbon dioxide - the best explanation for the existence of both is that they are generated by the hydrothermal reaction between the warm ocean under the ice and the seabed rock formations,This hydrothermal reaction can provide energy for deep-sea microorganisms.This is very similar to the environment where the earth was born and nurtured life billions of years ago.Scientists believe that Enceladus not only has a huge ocean, but also is protected by ice;Today, Enceladus has almost all the conditions needed for life - water, organic matter, and energy sources.Microbes powered by deep-sea hot springs may be hiding in the seabed.The research was published in the journal Science on the 14th.Hunter White, one of the authors of the paper and the person in charge of the Cassini mission, said that although the sulfur and phosphorus needed for life have not been found, it does not prevent Enceladus from "upgrading" to the place where extraterrestrial life is most likely to exist in the solar system.This discovery is regarded as the top achievement of Cassini's career, but the probe is now about to start its final journey through Saturn's halo.On September 15, it will enter the atmosphere of Saturn, officially ending its exploration mission.At the same time, the press conference announced that the Hubble Space Telescope found that Europa has a thin atmosphere containing oxygen, and took precious pictures of Europa or plumes formed by water vapor eruption.Scientists have always believed that Europa has a global ocean under its surface, whose water volume should be twice that of the Earth's oceans, and water is the most basic condition to support the existence of life.It is estimated that after 2020, NASA will launch the "Europa Fast Sail" project, make a close observation of Europa, and send a lander to focus on the huge ocean under the ice[13]。
A team led by scientists from the Southwest Research Institute of the United States, using the data provided by NASA's Cassini probe, detected phosphorus, the key element of life, in the oceans of Enceladus, which exists in the form of phosphate.Relevant research papers were published in the journal Nature on June 14, 2023.[17]
Hydrogen cyanide, the key substance of life origin
In December 2023, a research report published in the international academic journal Nature Astronomy said that hydrogen cyanide, a key material in the origin of life, was found on Saturn's moon Enceladus.The report said that in addition to hydrogen cyanide, researchers also detected organic molecular oxides, which further confirmed that some substance was driving the organic chemical reaction on Enceladus.Researchers say that while this still does not confirm the existence of life on Enceladus, it reinforces this possibility.[19]
world record
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Enceladus has set a record for the most geysers on a satellite.(Guinness World Records)[14]
