1979 Voyager missions that forever changed our
( 15 )impressions of these bodies.
All four of the moons, named after Jupiter’s
lovers in Greco-Roman mythology, probably
experienced early, heavy asteroid bombardment. The
very ancient, relatively unchanged surface of Callisto
( 20 )remains badly scarred by impact craters. The younger
surface of Ganymede shows more variety, featuring
distinctive light and dark areas. Ancient craters dot the
dark areas, while the light areas are crisscrossed by
ridges and grooves that resulted from more recent ice
( 25 )flows. The impact sites on Europa have almost
completely disappeared under vast oceans of ice.
But perhaps the biggest surprise of the Voyager
mission was the discovery of intense volcanic or
geyser-like activity on Io. Eruptions first recognized as
( 30 )plumes of dust and gas were immediately noticeable
on the Voyager photographs. Further inspection
revealed at least seven such events occurring all at
once on Io’s otherwise frigid surface—massive
plumes of material were being ejected from the
( 35 )surface of the satellite to form clouds 500 kilometers
high. At other points, scientists detected three hot
spots believed to be ponds of molten lava, sulfur, or
sodium overlain by a crust. The largest of these hot
lakes was estimated to have a greater surface area than
( 40 )the state of Hawaii.
39. Which of the following best tells what this passage is about?(A) Galileo’s invention of the telescope
(B) the discovery of the Galilean moons
(C) scientific knowledge about the solar system
(D) the damage caused by asteroid bombardment
(E) Jupiter’s four brightest moons40. This passage suggests that Galileo was one of the first scientists to