JUNE 11 RC#1

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

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 body

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