 | Jupiter, the giant planet. |
 Jupiter's Galilean moonsThe biggest and most important satellites of Jupiter are called Galilean moons. They were discovery in 1610 by Galileo Galilei. Since than they were very important to the understanding of the Solar System. Just with a small telescope we can see these four moons. As we can see by the following data, these four satellites diameter is like the one of our moon’.
 GANYMEDE Ganymede is the biggest satellite of the Solar System. Like many rock planets (for example, our moon), Ganymede has two different kinds of surface. Those dark regions are the oldest surfaces on Ganymede and the light-coloured regions have fewer craters and are therefore younger. The dark, angular "islands" on Ganymede's surface may be remnants of the ancient original crust. 4.5 billion years ago, it may have been completely covered with an ocean whose depth would be approximately 1000 Km. During the following 200 million years, the water iced and that is today a frozen ocean about 100 Km thick. Craters also tell us about the history of the younger, light-coloured terrain, which is covered with several grooves. The newer, lighter regions give evidence of tectonic activity that may have broken up the icy crust. A thin layer of ozone has been detected around Ganymede.  IO Io is nearest Galilean Moons from Jupiter and the celestial body with more volcanic activity. Infrared spectrometers on Voyager 1 detected sulphur and sulphur dioxide expelled material. With a hight between 70 and 280 Km, the eruptions are violents and lava come through the vulcanos with speeds around 300 and 1000 m/s. The most violent volcano, here on Earth, has eruptions with speeds only around 100 m/s. The nature of the expelled material (SO2 and others) give Io it brilliant colours and they variates between yellow, orange, red and black. Scientists thinks Îo’s vulcanos are responsable to the existenceof rings particles. Apparently, one fraction per second may run away from Io’s gravity and became part of Jupiter’s magnetosphere. Because it constantly renovation, in Io’s surface there aren’t crack or fissures as we can seein Callisto or Ganymede. In Greek mythology, Io was a young woman who has been seduced by Zeus. But he tranforme the poor goodness into a heifer, to protect her to Hera, his jealous wife.
EUROPA  Europa is about 670,900 Km from Jupiter's center and is the smallest of Jupiter's Galilean moons.It is less dense than our moon too and spetroscopic observations from Earth indicate that Europa has frozen water on its surface. This fact suggests that Europa is covered with ice. In this icy surface there are many cracks and streaks and they're 20 to 40 km wide. Europa's surface is like an ice-water version of tectonic plates. CALLISTO  Callisto is the outermost Galilean Satellite and it has almost the same size as Mercury. Callisto has a heavily cratered crust of frozen water. Like Ganymede, it seems to have a rocky core surrounded by an ocean of ice. The surface is completely covered with meteoric impact craters; there are no "plains" there. Although the exact rate of impact crater formation is not known, scientists estimate that it would require several billion years to accumulate the number of craters found on Callisto. Therefore, the moon must have been inactive at least that long, so it gives us fine record of the past. The absence of grooved ground suggests that tectonic activity never began on Callisto. Perhaps because of Callisto's bigger distance from Jupiter, the ocean that could be found on the satellite's surface froze more quickly than on Ganymede. |
Jupiter, the giant planet.