Ganymede and Callisto

The four largest moons of the planet Jupiter are called the Galilean moons because they were discovered by Italian astronomer Galileo Galilei( why mentioned?=> to point out an astronomical d________ that he made) in 1601. The two smallest, lo and Europa, o_____ closer to Jupiter than Ganymede and Callisto, the two largest. Ganymede and Callisto are similar in several ways but also have some profound differences. Several, particularly the similarity / dissimilarity between their surfaces, were first noticed when the Voyager 1 and Voyager 2 space probes passed through the Jovian system in 1979 and closely o________ Jupiter and its moons.

With a diameter of 5,268 kilometers, Ganymede is the largest moon in the solar system and is bigger than Mercury and nearly as large as Mars.(= It is larger / smaller in diameter than one of the planets in the solar system.) Were it not for the fact that Ganymede orbits Jupiter, it would likely be classified as a planet. Ganymede is extremely old, having formed around 4.5 billion years ago, which was roughly when Jupiter itself came into . Primarily composed / composing of ice and rock, Ganymede has a surface that is mainly ice. Yet its surface is not even in composition, for large areas of it are darker than other parts. These dark regions comprise / are comprised about forty percent of the moon’s surface and have many impact craters whereas the lighter regions have fewer craters despite being / they are the majority of the moon’s surface. (= It has some parts with many craters and other parts with smaller n_______ of them.) The light regions show evidence of recent geological activity, which may explain why they are more / less cratered. As for Ganymede’s interior, it is believed to have a solid, rocky core with layers of rock and ice between the core and the surface. Ganymede has a thin oxygen atmosphere sufficient / insufficient to support life and is the only moon in the solar system to have its own magnetosphere.(= it has tectonic forces that are at w____ changing the face of its surface.)

At 4,820 kilometers in diameter, Callisto is smaller than Ganymede, but the two are the same age. Similar to Ganymede, it is made of rock and ice and has a predominantly ice surface. (       ), Callisto’s surface is much darker than Ganymede’s and reflects little light. (= Callisto has a dark surface from which only a small amount of l______ is reflected.) Callisto is one of the most heavily cratered celestial objects in the solar system. The presence of so many craters indicates that Callisto has no t________ forces changing its surface, a fact that induces most astronomers to regard it as a d_____ world. (         ), the craters on Callisto have not been totally affected / unaffected; they are smoother than those on other worlds and l______ ⓐthe deep s and ⓑhigh perimeter walls ←the craters on Earth’s moon have. These characteristics may be a result of Callisto’s icy surface s_________ out the craters as the ice moves, something which also happens on Ganymede. (          ), like Ganymede, Callisto has a thin / thick atmosphere, but it is composed / consisted mainly of carbon dioxide.

It is highly unlikely that this theory will be proven until probes—or perhaps even manned missions—are sent to explore the surfaces of the moons themselves.

Another characteristic both moons share is that it is likely that at least one internal ocean exists on each of them. ❶Ganymede is believed to have one or more oceans stacked between the layers of ice making up its interior. ❷Furthermore, there is evidence suggesting that Callisto may have an internal ocean of unfrozen salt water between fifty and 200 kilometers beneath its surface. ❸Some astronomers speculate that each moon may contain a_____ life in its subsurface waters.❹

(→There is a strong  that both / one  of them have oceans under their surfaces.)

Most scientists agree that they harbor 뜻은?  extraterrestrial life in their oceans. T / F

As for the primary difference between the two moons, it is their s________, which were photographed up close by the Voyager probes. The high number of craters on Callisto is most likely the result of it?? - as well as many other objects in the solar system - being subjected to a massive series of impacts during the Late Heavy Bombardment Period approximately 3.8 billion years ago. Ganymede was also caught in this bombardment of celestial objects, yet it? orbits closer to Jupiter, so as the giant planet’s gravity pulled many meteorites toward it?, an even larger number managed to strike Ganymede. These impacts forced the icy surface to m____ and pushed rocks deep into / out of its core. The impacts drove heat into the core. This heat is still creating internal tectonic forces on Ganymede, which, in ______, cause its surface to change and many craters to appear / disappear over time.(→ There are tectonic forces at work on Ganymede because meteorites c________ with it heated the core of the moon.) Callisto, being further away from Jupiter, was hit with fewer / more impacts, which drove fewer rocks and less heat into its core: Resultantly, Callisto has had virtually no tectonic forces at work, so its surface has remained mostly unchanged for billions of years.

traumatic / sincere

stark / potential

=w

= be brought into being

= around 4.5 billion years

↔ t

dispersed/ trapped/

organized/ layered

to guess about the possible causes or effects of something, without knowing all the facts or details

~에 영향을 받은