Europa is the smallest of planet Jupiter's four largest moons and the second moonout from Jupiter. Until 1979, it was just another astronomy textbook statistic. Then came the close-up images obtained by the exploratory spacecraft Voyager 2, and within days, Europa was transformed--in our perception, at least--into one of the solar system's most intriguing worlds. The biggest initial surprise was the ahnost total lack of detail, especially from far away. Even at close range, the only visible features are thin, kinked brown lines resembling cracks in an eggshell. And this analogy is not far offthe mark.

The surface of Europa is almost pure water ice, but a nearly complete absence of craters indicates that Europa's surface ice resembles Earth's Antarctic ice cap. Theeggshell analogy may be quite accurate since the ice could be as little as a few kilometers thick--a tree shell around what is likely a subsurface liquid ocean that, in turn, encases a rocky core. The interior of Europa has been kept warm over the cons by tidal forces generated by the varying gravitational tugs of the other big moons as they wheel around Jupiter. The tides on Europa pull and relax in an endless cycle. The resulting internal heat keeps what would otherwise be ice melted almost to the surface. The cracklike marks on Europa's icy face appear to be fractures where water or slush oozes from below. Soon after Voyager 2's encounter with Jupiter in 1979, when the best images of Europa were obtained, researchers advanced the startling idea that Europa's subsurface ocean might harbor life. Life processes could have begun when Jupiter was releasing a vast store of internal heat. Jupiter's early heat was produced by the compression of the material forming the giant planet. Just as the Sun is far less radiant today than the primal Sun, so the internal heat generated by Jupiter is minor compared to its former intensity. During this warm phase, some 4.6 billion years ago, Europa's ocean may have been liquid right to the surface, making it a crucible for life.

10. What does the passage mainly discuss?

(A) The effect of the tides on Europa's interior

(B) Temperature variations on Jupiter's moons

(C) Discoveries leading to a theory about one of Jupiter's moons

(D) Techniques used by Voyager 2 to obtain close-up images

11. The word "intriguing" in line 5 is closest in meaning to

(A) changing

(B) perfect

(C) visible

(D) fascinating

12. In line 7, the author mentions "cracks in an eggshell" in order to help readers

(A) visualize Europa as scientists saw it in the Voyager 2 images

(B) appreciate the extensive and detailed informalion available by viewing Europa from far away

(C) understand the relationship of Europa to the solar system

(D) recognize the similarity of Europa to Jupiter's other moons

13. It can be inferred from the passage that astronomy textbooks prior to 1979

(A) provided many contradictory statistics about Europa

(B) considered Europa the most important of Jupiter's moons

(C) did not emphasize Europa because little information of interest was available

(D) did not mention Europa because it had not yet been discovered

14. What does the author mean by stating in line 7 that "this analogy is not far off the mark"?

(A) The definition is not precise.

(B) The discussion lacks necessary information.

(C) The differences are probably significant.

(D) The comparison is quite appropriate.

15. It can be inferred from the passage that Europa and Antarctica have in common which of the following?

(A) Both appear to have a surface with many craters.

(B) Both may have water beneath a thin, hard surface.

(C) Both have an ice cap that is melting rapidly.

(D) Both have areas encased by a rocky exterior.

16. The word "endless" in line 14 is closest in meaning to

(A) new

(B) final

(C) temporary

(D) continuous

17. According to the passage, what is the effect of Jupiter's other large moons on Eurnpa?

(A) They prevent Europa's subsurface waters from freezing.

(B) They prevent tides that could damage Europa's surface.

(C) They produce the very hard layer of ice that characterizes Europa.

(D) They assure that the gravitational pull on Europa is maintained at a steady level.

18. According to the passage, Voyager 2's images Ied rcsearchers to develop which of the following theories'?

(A) Jupiter may be hotter today than it once was.

(B) Europa is far older than scientists originally thought

(C) Europa's temperature is maintained by Jupiter's vast store of internal heat.

(D) The ocean waters of Europa could contain some forms of life.

19 The word "it" in line 24 refers to

(A) internal heat

(B) warm phase

(C) Europa's ocean

(D) surface

ĐÁP ÁN

10. C hay D?

11. D

12. A

13. A hay C?

14. D

15. B hay C?

16. D

17. A

18. D

19. C