Passage 3 | Astronomy
Io’s Volcanoes
In earlier periods of Earth’s history, the surface of our planet was a much more violent place than it is today. The core of the Earth is estimated to currently be between 3,000 and 55 5,000 degrees Celsius, but its temperature was even greater millions of years ago. This intense internal heat and pressure has been responsible for many of the processes that have shaped the surface of our planet over the ¡o millennia, such as tectonic shifts, earthquakes, and volcanoes. In a volcanic eruption, molten rock from deep inside the Earth is ejected out onto the surrounding landscape, significantly altering the physical and chemical makeup of the environment Scientists believe events like this were much more common and powerful in prehistoric times, and they study modem volcanic activity to better understand how Earth was shaped and formed.
[A] However, these processes are not unique to our world. [B] In fact, lo, one of the largest moons orbiting the planet Jupiter, is the most volcanically active celestial body known to exist. [C] The discovery of this fact has provided researchers with a new window into what our early planet may have looked like. [D]
It was not until the late 1970s that scientists were able to gather definitive 3t information about the surface features of Io. Probes launched by NASA around this time passed near the moon on their way to study Jupiter, Saturn, and the other outer planets. This provided the opportunity to capture photographs and take other kinds of measurements of lo. The probes’ detailed pictures of the moon revealed what turned out to be a very important, unexpected discovery. Scientists had anticipated that lo’s surface, like those of most other rock-based bodies that inhabit our solar system, would display the typical craters and impact marks from countless collisions over time with meteors and other objects adrift in space. They planned to use those marks to estimate the age of the moon’s surface by recording the amount of craters—the more craters, the older the surface. When scientists saw the probes’ images, however, they were shocked to see an absence of impact craters. As it turns out, lo’s surface is not very old, less than one million years.
Fortunately, the scientists were also able to observe the reason for this peculiarity: lo’s surface is covered with volcanoes. It is constantly changing as new volcanoes emerge, others become extinct, and magma deposits accumulate or disappear. Just like on Earth, these processes continually renew the moon’s surface, redistributing molten material from the interior to the exterior and subsequently covering all traces of impact marks, lo’s volcanic features are the reason for its youthful face.
The existence of volcanoes on lo was not the only interesting discovery. Photographs of the surface showed the volcanic activity to be extremely intense, with some eruptions spewing material as high as 300 kilometers. And, in addition to volcanoes, lo is covered by lava flows, volcanic geysers, and molten lakes. Taken together, these observations allowed scientists to confirm what had previously only been speculated about the cores of other moons and planets: like Earth’s, some of them are hot.
Part of the reason for its fiery interior, and hence also for its volcanic activity, has to do with lo’s somewhat unique orbital position, so During its orbit around Jupiter, the moon is constantly pulled by the gravity of that enormous planet. However, at some points, lo is also pulled in the opposite direction by the gravity of two other large moons whose orbits 3i sometimes put lo between them and Jupiter. These immense gravitational forces stretch and squish lo by as much as 100 meters. This motion generates internal friction, and the resulting heat melts lo’s interior, giving rise to its spectacular displays of volcanic activity.
Needless to say, the size and intensity of lo’s volcanoes are of great interest to scientists who believe that similar conditions may once have existed on Earth. By better understanding the nature of such conditions, we will have a better grasp of the formative processes that shaped our planet, lo thus offers scientists a rare opportunity to study an important aspect of Earth’s distant past.
26. The word ejected in the passage is closest in meaning to
(A) tom
(B) piled
(C) worn
(D) thrown
27. What can be inferred from paragraph 1 about Earth’s core temperature?
(A) It has decreased over time, but it will increase again in the future.
(B) Tectonic activity and earthquakes have no relation to core temperature.
(C) It must be above 5,000 degrees Celsius to produce volcanoes.
(D) Hotter temperatures produced more intense volcanic events.
28 Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
(A) Scientists knew that lo was a rock-based body because of all the meteor craters and other marks that were found on its surface. ,
(B) Most rocky bodies in the solar system are covered with collision craters, and researchers were expecting to see these on lo.
(C) Rock-based planets and moons usually have numerous impact marks because they are constantly colliding with small meteors and other particles.
(D) Even before scientists saw images of lo’s surface, they could predict the amount of craters and impact marks that would be visible there.
29. Why does the author mention Probes in paragraph 3?
(A) To explain how important discoveries about lo were made
(B) To describe the level of NASA’s interest in Jupiter’s moons
(C) To introduce similarities between lo and the outer planets
(D) To illustrate an outdated method of collecting data in space
30. According to paragraph 3, how do scientists determine the ages of rock-based moons?
(A) By comparing them with planets of known ages
(B) By measuring the circumference of the celestial body
(C) By observing the frequency of impact marks
(D) By analyzing the composition of the crust
31. The word traces in the passage is closest in meaning to
(A) sizes
(B) regions
(C) evidence
(D) combinations
32. Why does the author mention lava flows and volcanic geysers in paragraph 5?
(A) To discuss some characteristics shared by all rock-based moons and planets
(B) To state the features of lo’s surface that the probes were sent to photograph
(C) To explain that some natural processes are more powerful than volcanic eruptions
(D) To list observations that enabled scientists to determine the nature of the cores of other moons and planets
33. The word speculated in the passage is closest in meaning to
(A) written
(B) proved
(C) imagined
(D) understood
34. The word them in the passage refers to
(A) lakes
(B) cores
(C) moons
(D) planets
35. According to paragraph 6, what is responsible for lo’s molten core?
(A) The gravitational pull of the surrounding bodies
(B) The heat present when lo orbits close to the sun
(C) The moon’s own intense gravitational forces
(D) The volcanoes that heat and melt lo’s surface
36. What can be inferred from paragraph 6 about lo?
(A) It is larger than the two moons that orbit closest to it.
(B) It is the only moon in the solar system that has volcanoes.
(C) It orbits closer to Jupiter than some of the other moons.
(D) Its core measures less than 100 meters in diameter.
37. Look at the four squares [] that indicate where the following sentence could be added to the passage.
Most of the rocky planets and moons in our solar system experience similar events.
Where would the sentence best fit?
38. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Since the discovery that lo is the most volcanically active location in our solar system, scientists have been using it to learn about conditions on the early Earth.
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Answer Choices
(A) Instead of observing craters on lo’s surface, NASA’s probes revealed the presence of volcanic activity on the moon.
(C) It is impossible to determine the ages of planets and moons with active volcanoes because their surfaces are constantly changing.
(E) Many of the volcanoes currently active on Earth are similar to those on lo in terms of size.
(B) The volcanic activity on lo is so intense that the moon’s surface is constantly being recycled and renewed, similar to theories about what happened on Earth.
(D) Before scientists launched probes to photograph lo, they assumed that they would be able to estimate the moon’s age by observing its volcanoes.
(F) Because of the peculiarities in the orbiting patterns of Jupiter’s moons, lo experiences intense gravitational forces that heat its core.
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