The Galilean moon of Jupiter was an Italian astronomer in 1610Galileo Galilei The four satellites of Jupiter first discovered by telescope areIo、Europa、GanymedeandGanymede, whose names are "Io", "Europa", "Ganymede" and "Callisto" in order[1]。
Io Io is a volcanic satellite with more than 400 active volcanoes on its surface, so Io is also the most geologically active celestial body in the solar system;Europa Europa is the smallest of the Galilean satellites of Jupiter. Its surface is generally smooth, and it is the smoothest celestial body in the solar system. Due to the small number of impact craters, Europa is also one of the satellites with the highest surface geometric albedo;Ganymede is the largest satellite in the solar system and the only known satellite with a magnetic circle in the solar system;The surface geometric albedo of Callisto, Ganymede, the farthest from Jupiter in the Galileo satellite, is only 0.2, but there are patches of terrain composed of pure ice on the surface of Ganymede with a geometric albedo as high as 0.8[1]。
Galileo satellite isJupiterThe four satellites of Io, Europa, Ganymede and Callisto were discovered by Italian astronomer Galileo in 1610, hence their names.Their orbits are circularTrack planeAlmost all of them are similar to Jupiter'sEquatorial surfaceCoincidence, the rotation period is the same as that of Jupiter, which is the four larger satellites in the solar system[3]。
Discovery History
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On January 7, 1610, Galileo observed that there were two bright small stars in the east of Jupiter, and there was a small star in the west of Jupiter.On January 8, three small stars appeared around Jupiter, also on both sides of Jupiter, and lined up.On January 9, the sky was cloudy, and no observation activities were carried out.On January 10, there are only two small stars around Jupiter.Galileo speculated that another might be blocked by Jupiter.On January 11, Galileo concluded that these three small stars all move around Jupiter, just like Venus, Saturn and the sun.On January 13, Galileo found the fourth small star around Jupiter, and noticed that the small star did not shine.Galileo did not stop observing until March 2, when Galileo definitely concluded that these four small stars were all Jupiter's moons and moved around Jupiter.Galileo immediately told others about his new discovery, and made a public speech and presentation at Padua University, announcing his new astronomical discovery[2]。
name
The four Galileo satellites were named after Dutch astronomers of German originSimon Marius(Simon marius) (1573-1624), he also claimed that he had discovered them before Galileo[4]。
significance
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The discovery of these satellitesHeliocentric systemThe establishment of has played a historic role.Danish astronomer in the 1770sRomerIt was through the eclipse of Galileo's satellite by Jupiter that the propagation speed of light was measured for the first time.Since the 17th century, many achievements have been made in the study of Galileo satellites[3]。
Io
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Io is the most inboard of Jupiter's four Galilean satellites. Its orbit is 422000 kilometers away from Jupiter, and its diameter is about 3630 kilometers. Besides Earth, Io is the only planet in the solar system that has been confirmed to have frequent volcanic activities.Due to Io's weak gravity, the debris ejecta generated by the large-scale eruption will rise to a very high position.[5]
Io has a thin atmospheresulfur dioxideComposed with other gases.Unlike the satellites of the outer solar system, Io and Europa are composed ofterrestrial planetSimilarly, it is mainly composed of hot silicate rocks.Its surface is also very different from other stars in the solar system, which makes scientists first contactVoyagerThe data sent back was very surprising.They originally thought that the earth like stars should be covered with craters of all sizes left by the impact, and then estimated the age of the planet's crust by the "crater" left in the unit area.In fact, there are few craters on the surface of Io.In this way, its surface is very young[6]。
Io has an amazing variety of landforms: there are volcanic craters thousands of meters deep down, hot sulfur lakes, obvious non volcanic mountains, hundreds of kilometers of viscous liquid flowing, and some volcanic vents.The multiple colors of sulfur and its compounds make Io's surface colorful[6]。
Io
The hottest spot on Io's surface can reach 700K, although its average temperature is only about 130K.These hot spots are the main reason for Io's loss of heat.Unlike other satellites discovered by Galileo, Io has almost no water.This may be because Jupiter was too hot at the beginning of the evolution of the solar system, which evaporated the volatile substances of Io[6]。
yesVoyagerThe analysis of the images made scientists believe that the lava flows on Io's surface are mostly composed of hot sulfur compounds.However, the following surface based research shows that there will be no liquid sulfur if the temperature is too high.One current theory is that Io's lava flow is made up of hot silicate rocks.currenthubble space telescope The observation shows that those substances may be rich in sodium, or that there are different components in different places[6]。
The energy required for all the activities of Io may come from the interactive tidal force between Io and Europa, Ganymede and Jupiter.The co motion of the three satellites is fixed. Io's orbital period is twice that of Europa, and the latter is twice that of Ganymede.Although Io is like the moon, the satellite of the earth, with only a fixed side facing its main star, it is slightly unstable due to the role of Europa and Ganymede.It twists and bends Io, about 100 meters long, and generates energy in the cycle of restoring the distortion.Io also cuts Jupiter's magnetic field lines, generating currents.The resulting energy is not much for the tidal force, but the power of the current is still 1 megawatt.It also stripped off some of the material of Io, and generated strong convex radiation around Jupiter.The detached particles in the bulge partially created Jupiter's giant magnetosphere[6]。
come fromGalileoThe latest data of Ganymede shows that Io may have its own magnetic field, just like Ganymede[6]。
Europa
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Europa is the sixth known satellite of Jupiter and the fourth largest satellite of Jupiter. It is slightly smaller than the moon, with a diameter of 3138 kilometers. It was discovered by Galileo in 1610.Europa's composition andterrestrial planetSimilar: mainly composed of silicate rocks.But unlike Io, Europa has a thin ice shell[7]。
Europa
There are few craters on Europa;Only three craters with a diameter of more than 5km were found.Photos of Europa's surface are similar to those of ice on Earth's oceans.This may be because there is a layer of liquid water under the ice on Europa's surface, perhaps 50 kilometers deep, which is kept liquid by the heat brought by the tidal force.If so, this will be the only place in the solar system where there is a large amount of liquid water besides the Earth[7]。
Europa has a thin atmosphere containing oxygen.Unlike the oxygen in Earth's atmosphere, Europa's is not biologically formed.It is most likely that charged particles in the sunlight hit Europa's icy surface to generate water vapor, which is divided into hydrogen and oxygen.Hydrogen disengages, leaving oxygen behind[7]。
Europa is the brightest satellite in the solar system. For hundreds of years, it has fascinated many scientists with its uniqueness.The reason why it looks so bright is that it has a layer of ice shell on its surface, which can strongly reflect the sunlight.At present, the scientific community generally believes that Europa has no land on its surface, and there is a vast ocean under the cold shell ice, which has much more water than the earth has.The ocean is absorbing a lot of oxygen, even more than the prediction model shows.Some areas of the seabed should be very similar to the environment around the earth's deep-sea hot springs, and its composition is enough to support the survival of a variety of life forms[7]。
Ganymede
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Ganymede is the largest known satellite of Jupiter, and also the seventh Jupiter satellite discovered. Among the satellites discovered by Galileo, Ganymede is the third closest to Jupiter.Ganymede is 1070000 kilometers away from Jupiter, with a diameter of 5262 kilometers and a mass of 1.48e23 kilograms.Its diameter is larger than Mercury, its mass is about half of Mercury, and it is also the largest satellite in the solar system[8]。
GanymedeIt was discovered by Galileo in 1610.But in fact, more than 2000 years ago, Gande, a famous astronomer of Chu State, discovered it during the Warring States Period. But because science was not widely popularized at that time, this conclusion was considered as fallacy.It was not until Galileo's discovery in 1610 that this statement was confirmed[8]。
Ganymede is a satellite orbiting Jupiter.It is the largest satellite in the solar system, with a diameter of about 5276 kilometers.Ganymede can circle Jupiter in just over a week, 1070000 kilometers away[8]。
stayGalileoBefore contacting Ganymede, it was generally believed that Ganymede and Ganymede were a piece of rocky material wrapped with a large water or ice water mixture as the mantle, and had an ice crust (similar to Titan and Triton).Preliminary data from Galileo suggest that Ganymede has a unique composition, while Ganymede has three layers: a small iron or iron sulfide core, silicate rock mantle outside, and ice crust outside.In fact, Ganymede is very similar to Io except for an ice shell[8]。
The surface of Ganymede is very rough, and there are two kinds of landforms: very old dark areas with meteorite craters, and relatively young bright areas with large grooves and ridges.Their origin is obviously due to natural structure, but the details are not very clear.In this respect, Ganymede may be similar to Earth, Venus or Mars[8]。
Ganymede
hubble space telescope It is found that Ganymede has thin oxygen atmosphere, which is very similar to that found on Europa.Similar grooves and ridges are also visible on Enceladus, Rhea and Triton.The dark zone is similar to the surface of Ganymede[8]。
There are extended craters on both landforms. The density of the craters reflects that they are 30-35 billion years old, not much like the moon.The crater is sometimes cut by grooves, indicating that the grooves are also very old.The relatively young crater can also be seen through the light emitted.But unlike the moon, it has flat craters and lacks ring-shaped mountains. The central depression is usually the same as that on the moon and Mercury.This may be because Ganymede's ice crust is relatively fragile, making geological flow and lack of undulation.The ancient ring mountain is gradually erased, often called "painting"[8]。
GalileoWhen the aircraft first flew past Ganymede, it found that it had its own magnetic field, which was contained in Jupiter's giant magnetic field.This may be similar to the Earth: the result of the movement of matter inside the stars[8]。
The researchers found that under the rugged ice layer on the surface of Ganymede, there may be a liquid salt water ocean.The existence of groundwater is an important indicator of whether there are signs of life on the planet.This latest result makes Ganymede the third Jupiter satellite with underground water sources.The other two similar satellites are Europa and Ganymede.Researchers are analyzingNASANASA's Galileo spacecraft found a possible underground ocean[8]。
Ganymede
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Ganymede
Ganymede is the second largest moon of Jupiter, with a diameter of 4821 kilometers and a small average density, which means that water accounts for more than half.It has no atmosphere. The craters on its surface are almost saturated, and there is no flat plain like the dark moon sea;On the other hand, it lacks young meteorite craters with bright radiation stripes on its surface, and also lacks evidence of tectonic activity to infer that its surface is very old (at least as old as the Moon Sea, because in the later years, there was little or no geological activity such as upwelling of internal materials, and the ice surface was darkened due to the accumulation of meteorite dust)[9]。
