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.
1. The primary purpose of the passage is best expressed as
· The author discusses the method of data utilization
that proved that the moon was once part of the earth.
· The author discusses the methods of data utilization
that changed scientists’ opinions about the relative
sizes of the earth’s and moon’s cores.
· The passage studies the method that, using data
about radii and core mass, led to important
implications about the origin of the planets.
· The passage studies the use of scientific methods to
analyze data and confirm a hypothesis and references
possible deductions.
· 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
· changes in a spacecraft’s velocity as it returned to
Earth
· changes in the gravitational pull on the Lunar
Prospector as it orbited the moon
· changes in the moon’s gravity as it orbited the earth
· changes in a spacecraft’s radio signals as it changed
position relative to the earth
· changes in the moon’s gravitational pull over time
3. The author mentioned “gravity map” in the second
paragraph in order to
· illustrate the method used to correct the Lunar
Prospector’s velocity
· confirm the results obtained by examining the moon’s
magnetic field
· detail a step in the investigation of the composition
of a specific orbiting
· detail a step in the investigation of the effects of
gravity on the moon and earth
· 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
· 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
· a comparison of the earth’s and moon’s cores
suggests that the earth did break away from the moon
· 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
· 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
· the moon’s core has a higher ratio of iron in its
composition than does the earth’s![]()
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.
1. The primary purpose of the passage is best expressed as
· The author discusses the method of data utilization
that proved that the moon was once part of the earth.
· The author discusses the methods of data utilization
that changed scientists’ opinions about the relative
sizes of the earth’s and moon’s cores.
· The passage studies the method that, using data
about radii and core mass, led to important
implications about the origin of the planets.
· The passage studies the use of scientific methods to
analyze data and confirm a hypothesis and references
possible deductions.
· 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
· changes in a spacecraft’s velocity as it returned to
Earth
· changes in the gravitational pull on the Lunar
Prospector as it orbited the moon
· changes in the moon’s gravity as it orbited the earth
· changes in a spacecraft’s radio signals as it changed
position relative to the earth
· changes in the moon’s gravitational pull over time
3. The author mentioned “gravity map” in the second
paragraph in order to
· illustrate the method used to correct the Lunar
Prospector’s velocity
· confirm the results obtained by examining the moon’s
magnetic field
· detail a step in the investigation of the composition
of a specific orbiting
· detail a step in the investigation of the effects of
gravity on the moon and earth
· 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
· 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
· a comparison of the earth’s and moon’s cores
suggests that the earth did break away from the moon
· 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
· 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
· the moon’s core has a higher ratio of iron in its
composition than does the earth’s