Before the age of space exploration, the size and composition of the moon's core were astronomical mysteries. Astronomers assumed that the moon's core was smaller than that of the Earth, in both relative and absolute terms — the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass — but they had no way to verify their assumption. However, data gathered by Lunar Prospector have now given astronomers the ability to determine that the moon's core accounts for 20 percent of the moon's radius and for a mere 2 percent of its overall mass.
The data have been used in two ways. In the first method, scientists measured minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the Earth. These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the moon. These changes resulted from inconsistency in the gravitational pull of the moon on the craft, and permitted scientists to create a "gravity map" of both near and far sides of the moon. This map, in turn, revealed to scientists the distribution of the moon's internal mass. Scientists were then able to determine that the moon has a small, metallic core, which, if composed mostly of iron, has a radius of approximately 350 kilometers. The second method involved examining the faint magnetic field generated within the moon itself by the moon's monthly passage through the tail of the Earth's magnetosphere. This approach confirmed the results obtained through examination of the gravity map.
The size and composition of the moon's core are not academic concerns; they have serious implications for our understanding of the moon's origins. For example, if the moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that the moon was once part of the Earth and broke away at an early stage in the Earth's evolution, perhaps as the result of a major asteroid impact. The impact could have loosened iron that had not already sunk to the core of the Earth, allowing it to form the core around which the moon eventually coalesced. Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon.
1. The primary purpose of the passage is best expressed as
(A) The author discusses the method of data utilization that proved that the moon was once part of the earth.
(B) The author discusses the methods of data utilization that changed scientists' opinions about the relative sizes of the earth's and moon's cores.
(C) The passage studies the method that, using data about radii and core mass, led to important implications about the origin of the planets.
(D) The passage studies the use of scientific methods to analyze data and confirm a hypothesis and references possible deductions.
(E) The passage discusses the implications following from the size of the Earth's core.
2. According to the passage, scientists employed one research method that measured
(A) changes in a spacecraft's velocity as it returned to Earth
(B) changes in the gravitational pull on the Lunar Prospector as it orbited the moon
(C) changes in the moon's gravity as it orbited the earth
(D) changes in a spacecraft's radio signals as it changed position relative to the earth
(E) changes in the moon's gravitational pull over time
3. The author mentioned “gravity map” in the second paragraph in order to
(A) illustrate the method used to correct the Lunar Prospector’s velocity
(B) confirm the results obtained by examining the moon’s magnetic field
(C) detail a step in the investigation of the composition of a specific orbiting
(D) detail a step in the investigation of the effects of gravity on the moon and earth
(E) explain a step in the process of confirming a new hypothesis and discarding an older theory
4. It can be inferred from the passage that
(A) the earth’s core contributes a higher proportion of both the earth’s total radius and its total mass than the core of the moon contributes to its own total radius and mass
(B) a comparison of the earth’s and moon’s cores suggests that the earth did break away from the moon
(C) scientists will eventually be able to use the gravity map to further the proof that a major asteroid impact caused the earth and moon to separate
(D) because the earth and moon were once joined, it is probable that scientists will eventually discover fossils and other evidence on the moon that indicates that a major asteroid impact caused the extinction of the dinosaurs
(E) the moon’s core has a higher ratio of iron in its composition than does the earth’s
5. According to the passage, the magnetic field within the Moon’s core
(A) confirms the inconsistencies in radio signal wavelength detected by the Lunar Prospector
(B) is produced when the Moon moves through the Earth’s magnetosphere
(C) calls the results of the radio signal analysis into question
(D) permits the creation of a gravity map corresponding to lunar mass concentrations
(E) indicates the speed and direction of travel of the Moon
6. If the wavelength of radio signals emitted by the Lunar Prospector were constant, then which of the following could be most properly inferred?
(A) The velocity of the spacecraft depends on whether it is on the near or far side of the Moon.
(B) The size and mass of the Moon’s core may be more comparable to the size and mass of the Earth’s core than is currently believed.
(C) As the craft orbits the moon, the Moon exerts a constant gravitational pull on the craft.
(D) The Earth and the Moon seem to have originated independently.
(E) It would be impossible to create a gravity map of the Moon.
7. In the last sentence of the passage, the author uses the word “so-called” primarily in order to imply that
(A) the force may not have been adequate to cause the claimed ejection
(B) fission theory may have less explanatory power than impact theory
(C) the later coalescence of the Moon’s material may not have occurred as a result of centrifugal force
(D) the speed of the early Earth’s rotation may have led to the creation of the Moon
(E) the phenomenon in question might more properly be re-named
DDCABCE
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2021-4-29 21:04:38
收藏
收藏
