The Galilean


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They are, however, guaranteed free board and lodging, a place on two foreign language courses, plus personal tutoring to help them plan their university careers. Admission to the first year at the Scuola Galileiana di Studi Superiori is subjected to passing an entrance examination.

If accepted, students are then required to maintain a high average for their entire degree course. In addition to the 30 above-mentioned places, the Galilean School of Higher Education recruits up to 4 highly-motivated foreign students , intentioned to enroll in a 2-year program towards the Master Degree Second Cycle Degree, in Italian Laurea Magistrale.

These students are admitted at the 4th year of the Galilean School. Massimo 33 - Padova tel. Uniweb Departments Schools. The more craters, the longer the surface has been exposed to battering from space, and the older it must therefore be. If we judge from crater counts, this fresher terrain on Ganymede is somewhat younger than the lunar maria or the martian volcanic plains, perhaps 2 to 3 billion years old. The differences between Ganymede and Callisto are more than skin deep. Ganymede is a differentiated world, like the terrestrial planets. In addition, the Galileo spacecraft discovered that Ganymede has a magnetic field, the sure signature of a partially molten interior.

There is very likely liquid water trapped within the interior. Thus, Ganymede is not a dead world but rather a place of intermittent geological activity powered by an internal heat source.

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Some surface features could be as young as the surface of Venus a few hundred million years. The younger terrain was formed by tectonic and volcanic forces Figure In some places, the crust apparently cracked, flooding many of the craters with water from the interior. Extensive mountain ranges were formed from compression of the crust, forming long ridges with parallel valleys spaced a few kilometers apart.


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In some areas, older impact craters were split and pulled apart. There are even indications of large-scale crustal movements that are similar to the plate tectonics of Earth. Why is Ganymede so different from Callisto? Possibly the small difference in size and internal heating between the two led to this divergence in their evolution. Ganymede is close enough to Jupiter that tidal forces from the giant planet may have episodically heated its interior and triggered major convulsions on its crust.

A tidal force results from the unequal gravitational pull on two sides of a body. In a complex kind of modern dance, the large moons of Jupiter are caught in the varying gravity grip of both the giant planet and each other. This leads to gravitational flexing or kneading in their centers, which can heat them—an effect called tidal heating.

A fuller explanation is given in the section on Io. We will see as we move inward to Europa and Io that the role of jovian tides becomes more important for moons close to the planet. Europa and Io, the inner two Galilean moons, are not icy worlds like most of the moons of the outer planets. With densities and sizes similar to our Moon, they appear to be predominantly rocky objects. How did they fail to acquire a majority share of the ice that must have been plentiful in the outer solar system at the time of their formation? The most probable cause is Jupiter itself, which was hot enough to radiate a great deal of infrared energy during the first few million years after its formation.

This infrared radiation would have heated the disk of material near the planet that would eventually coalesce into the closer moons. Thus, any ice near Jupiter was vaporized, leaving Europa and Io with compositions similar to planets in the inner solar system. Despite its mainly rocky composition, Europa has an ice-covered surface, as astronomers have long known from examining spectra of sunlight reflected from it. There are very few impact craters in this ice, indicating that the surface of Europa is in a continual state of geological self-renewal.

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Judging from crater counts, the surface must be no more than a few million years old, and perhaps substantially less. In terms of its ability to erase impact craters, Europa is more geologically active than Earth. When we look at close-up photos of Europa, we see a strange, complicated surface Figure For the most part, the icy crust is extremely smooth, but it is crisscrossed with cracks and low ridges that often stretch for thousands of kilometers. Some of these long lines are single, but most are double or multiple, looking rather like the remnants of a colossal freeway system.

It is very difficult to make straight lines on a planetary surface. We now know the lines on Mars were optical illusions, but the lines on Europa are real. These long cracks can form in the icy crust if it is floating without much friction on an ocean of liquid water Figure The close-up Galileo images appear to confirm the existence of a global ocean.

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In many places, the surface of Europa looks just as we would expect for a thick layer of ice that was broken up into giant icebergs and ice floes and then refrozen in place. When the ice breaks, water or slush from below may be able to seep up through the cracks and make the ridges and multiple-line features we observe. Many episodes of ice cracking, shifting, rotating, and refreezing are required to explain the complexity we see.

The icy crust might vary in thickness from a kilometer or so up to 20 kilometers. If Europa really has a large ocean of liquid water under its ice, then it may be the only place in the solar system, other than Earth, with really large amounts of liquid water. Hot or at least warm springs might be active there, analogous to those we have discovered in the deep oceans of Earth. The necessary internal heat is generated by tidal heating see the discussion later in this chapter.

A short film with planetary scientist Kevin Hand explains why Europa is so interesting for future exploration. Or listen to this more in-depth talk on Europa. Is it possible that similar ecosystems could exist today under the ice of Europa? Many scientists now think that Europa is the most likely place beyond Earth to find life in the solar system. In response, NASA is designing a Europa mission to characterize its liquid ocean and its ice crust, and to identify locations where material from inside has risen to the surface. Such interior material might reveal direct evidence for microbial life.

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In planning a future mission, it may be possible to include a small lander craft as well. We might therefore expect it to have experienced a similar history. Its appearance, as photographed from space, tells us another story, however Figure Instead of being a dead cratered world, Io turns out to have the highest level of volcanism in the solar system, greatly exceeding that of Earth. Eight volcanoes were seen erupting when Voyager 1 passed in March , and six of these were still active four months later when Voyager 2 passed. With the improved instruments carried by the Galileo spacecraft, more than 50 eruptions were found during alone.

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Many of the eruptions produce graceful plumes that extend hundreds of kilometers out into space Figure Watch a brief movie made from Voyager and Galileo data, showing a rotating Io with its dramatic surface features. The Galileo data show that most of the volcanism on Io consists of hot silicate lava, like the volcanoes on Earth.

Sometimes the hot lava encounters frozen deposits of sulfur and sulfur dioxide. When these icy deposits are suddenly heated, the result is great eruptive plumes far larger than any ejected from terrestrial volcanoes. Major new surface features were even seen to appear between Galileo orbits, as shown in Figure As the Galileo mission drew to a close, controllers were willing to take risks in getting close to Io. Indeed, in its very first pass by Io, the spacecraft absorbed damaging radiation beyond its design levels.

To keep the system working at all, controllers had to modify or disable various fault-protection software routines in the onboard computers. In spite of these difficulties, the spacecraft achieved four successful Io flybys, obtaining photos and spectra of the surface with unprecedented resolution.

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Maps of Io reveal more than recently active volcanoes. From these measurements, it seems clear that the bright surface colors that first attracted attention to Io are the result of a thin veneer of sulfur compounds. The underlying volcanism is driven by eruptions of molten silicates, just like on Earth Figure How can Io remain volcanically active in spite of its small size? The answer, as we hinted earlier, lies in the effect of gravity, through tidal heating. Io is about the same distance from Jupiter as our Moon is from Earth.

Yet Jupiter is more than times more massive than Earth, causing forces that pull Io into an elongated shape, with a several-kilometer-high bulge extending toward Jupiter.

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