Of Jupite’s four largest moons, known as the Galilean moons, lo is the closest to Jupiter and the densest. lo is the most geologically active object in the entire solar system. In all, more than 80 active volcanoes have been identified on lo. In contrast to the surfaces of he other Galilean moons, its surface is neither cratered nor streaked but is instead exceptionally smooth, mostly varying in altitude by less than one kilometer. This smoothness is apparently the result of molten matter that constantly fills in any dents and cracks, giving lo the youngest surface of any known object in the solar system.
Io’s volcanism has a major effect on Jupiter s magnetosphere(the space around a planet affected by its magnetic field). All the Galilean moons orbit within the magnetosphere and play some part in modifying its properties, but lo’s influence is particularly marked. Although many of the electrically charged particles(ions)in Jupiter s magnetosphere come from the solar wind, there is strong evidence that lo’s volcanism is the predominant source of heavy ions in the Inner regions. Jupiter s magnetic field continually sweeps past lo gathering up the particles that lo’s volcanoes spew into space and accelerating them to high speed. The result is the lo plasma torus, a doughnut-shaped region of gas that has been heated to such high temperatures that its atoms are ionized. The plasma torus completely encircles Jupiter along the path of lo’s orbit. The plasma torus is quite easily detectable from Earth, but before the explorations of the United States Voyager space probes, its origin was unclear. Later the Galileo spacecraft made detailed studies of the plasma torus. Its spectroscopic analysis shows that sulfur is one of the torus s major constituents, strongly implicating lo’s volcanoes as its cause.
It must be asked what causes such astounding volcanic activity on lo, since, left to itself, lo would long ago have become geologically inactive, like Earths Moon, whose once molten interior has cooled below the temperature needed to support volcanic activity. Before the origin of the plasma torus was understood, some scientists suggested that the process by which the magnetosphere created the plasma was also heating lo. We now know that this is not the case. The real source of lo’s volcanic activity is gravity-Jupiter’s gravity. Two factors are at issue. First, lo orbits very close to Jupiter. As a result, Jupiter’s huge gravitational field exerts strong forces on he moon. These forces are so large that they pull the surface of lo into a raised area or bulge that points toward Jupiter. Second, lo s orbit is not perfectly circular. If lo were the only moon orbiting Jupiter. It would long ago have come into a state in which its rotation on its axis was perfectly synchronized with its revolution around Jupiter. I that case, lo would move in a perfectly circular orbit with the same side unvaryingly turned toward Jupiter.
But lo Is not alone. As it orbits, it is constantly pulled by the gravity of its nearest large neighbor, another Galilean moon. Europa. Although Europa’s pull on lo is small. it is sufficient to make lo’s orbit slightly noncircular. In a noncircular orbit, the moons speed varies from place to place as it moves in its orbit around Jupiter but its rate of rotation on its axis remains constant. Thus it cannot keep the same face steadily turned toward Jupiter. Instead, as seen from Jupiter, lo turns slightly from side to side as it moves. On the other hand, the large tidal bulge on los surface caused by Jupiters gravity always points directly toward Jupiter, so it moves back and forth across lo’s surface as the moon wobbles. Those conflicting forces result in enormous tidal stresses that continually flex and squeeze lo’s interior.
Just as frequent back-and-forth bending of a piece of wire can produce heat through friction, the ever-changing distortion of lo’s interior constantly heats the moon. This generation of large amounts of heat within lo ultimately causes huge jets of gas and molten rock to squirt out of the moons surface. Galileos sensors indicated extremely high temperatures in the outflowing material. Researchers estimate that the total amount of heat generated within lo as a result of tidal flexing is about 100 million megawatts.
1
Of Jupite’s four largest moons, known as the Galilean moons, lo is the closest to Jupiter and the densest. lo is the most geologically active object in the entire solar system. In all, more than 80 active volcanoes have been identified on lo. In contrast to the surfaces of he other Galilean moons, its surface is neither cratered nor streaked but is instead exceptionally smooth, mostly varying in altitude by less than one kilometer. This smoothness is apparently the result of molten matter that constantly fills in any dents and cracks, giving lo the youngest surface of any known object in the solar system.
According to paragraph 1, which of the following is NOT true of lo?
AIt is the largest of the four Galilean moons
BIt is the densest of Jupiter’s Galilean moons
CIt has more than 80 active volcanoes
DIts surface is much more even than those of other Galilean moons
2
Io’s volcanism has a major effect on Jupiter s magnetosphere(the space around a planet affected by its magnetic field). All the Galilean moons orbit within the magnetosphere and play some part in modifying its properties, but lo’s influence is particularly marked. Although many of the electrically charged particles(ions)in Jupiter s magnetosphere come from the solar wind, there is strong evidence that lo’s volcanism is the predominant source of heavy ions in the Inner regions. Jupiter s magnetic field continually sweeps past lo gathering up the particles that lo’s volcanoes spew into space and accelerating them to high speed. The result is the lo plasma torus, a doughnut-shaped region of gas that has been heated to such high temperatures that its atoms are ionized. The plasma torus completely encircles Jupiter along the path of lo’s orbit. The plasma torus is quite easily detectable from Earth, but before the explorations of the United States Voyager space probes, its origin was unclear. Later the Galileo spacecraft made detailed studies of the plasma torus. Its spectroscopic analysis shows that sulfur is one of the torus s major constituents, strongly implicating lo’s volcanoes as its cause.
The word “properties” in the passage is closest in meaning to
Acharacteristics
Bmovements
Ceffects
Dpositions
3
Io’s volcanism has a major effect on Jupiter s magnetosphere(the space around a planet affected by its magnetic field). All the Galilean moons orbit within the magnetosphere and play some part in modifying its properties, but lo’s influence is particularly marked. Although many of the electrically charged particles(ions)in Jupiter s magnetosphere come from the solar wind, there is strong evidence that lo’s volcanism is the predominant source of heavy ions in the Inner regions. Jupiter s magnetic field continually sweeps past lo gathering up the particles that lo’s volcanoes spew into space and accelerating them to high speed. The result is the lo plasma torus, a doughnut-shaped region of gas that has been heated to such high temperatures that its atoms are ionized. The plasma torus completely encircles Jupiter along the path of lo’s orbit. The plasma torus is quite easily detectable from Earth, but before the explorations of the United States Voyager space probes, its origin was unclear. Later the Galileo spacecraft made detailed studies of the plasma torus. Its spectroscopic analysis shows that sulfur is one of the torus s major constituents, strongly implicating lo’s volcanoes as its cause.
According to paragraph 2, lo‘s volcanoes affect Jupiter in which of the following ways?
AThey produce ions that enter Jupiter’s magnetosphere
BThey speed up the solar winds that surround Jupiter
CThey increase the surface temperature of Jupiter
DThey produce the sulfur that covers the surface of Jupiter
4
Io’s volcanism has a major effect on Jupiter s magnetosphere(the space around a planet affected by its magnetic field). All the Galilean moons orbit within the magnetosphere and play some part in modifying its properties, but lo’s influence is particularly marked. Although many of the electrically charged particles(ions)in Jupiter s magnetosphere come from the solar wind, there is strong evidence that lo’s volcanism is the predominant source of heavy ions in the Inner regions. Jupiter s magnetic field continually sweeps past lo gathering up the particles that lo’s volcanoes spew into space and accelerating them to high speed. The result is the lo plasma torus, a doughnut-shaped region of gas that has been heated to such high temperatures that its atoms are ionized. The plasma torus completely encircles Jupiter along the path of lo’s orbit. The plasma torus is quite easily detectable from Earth, but before the explorations of the United States Voyager space probes, its origin was unclear. Later the Galileo spacecraft made detailed studies of the plasma torus. Its spectroscopic analysis shows that sulfur is one of the torus s major constituents, strongly implicating lo’s volcanoes as its cause.
According to paragraph 2, what did the Galileo spacecraft reveal about he plasma torus?
AThat it sometimes extends beyond Jupiter‘s magnetosphere
BThat its temperatures are so high that the atoms within it are ionized
CThat sulfur makes up much of it
DThat it matches up exactly with the path of lo‘s orbit
5
It must be asked what causes such astounding volcanic activity on lo, since, left to itself, lo would long ago have become geologically inactive, like Earths Moon, whose once molten interior has cooled below the temperature needed to support volcanic activity. Before the origin of the plasma torus was understood, some scientists suggested that the process by which the magnetosphere created the plasma was also heating lo. We now know that this is not the case. The real source of lo’s volcanic activity is gravity-Jupiter’s gravity. Two factors are at issue. First, lo orbits very close to Jupiter. As a result, Jupiter’s huge gravitational field exerts strong forces on he moon. These forces are so large that they pull the surface of lo into a raised area or bulge that points toward Jupiter. Second, lo s orbit is not perfectly circular. If lo were the only moon orbiting Jupiter. It would long ago have come into a state in which its rotation on its axis was perfectly synchronized with its revolution around Jupiter. I that case, lo would move in a perfectly circular orbit with the same side unvaryingly turned toward Jupiter.
What does the author imply in paragraph 3 by mentioning that Earth’s Moon is now geologically inactive?
Alo is closer to Jupiter than the Moon is to Earth
Blo is much younger than the Moon
Clo’s volcanoes eventually will disappear
DIo’s continued Volcanic activity is surprising.
6
But lo Is not alone. As it orbits, it is constantly pulled by the gravity of its nearest large neighbor, another Galilean moon. Europa. Although Europa’s pull on lo is small. it is sufficient to make lo’s orbit slightly noncircular. In a noncircular orbit, the moons speed varies from place to place as it moves in its orbit around Jupiter but its rate of rotation on its axis remains constant. Thus it cannot keep the same face steadily turned toward Jupiter. Instead, as seen from Jupiter, lo turns slightly from side to side as it moves. On the other hand, the large tidal bulge on los surface caused by Jupiters gravity always points directly toward Jupiter, so it moves back and forth across lo’s surface as the moon wobbles. Those conflicting forces result in enormous tidal stresses that continually flex and squeeze lo’s interior.
Why does the author state that”as seen from Jupiter, lo turns slightly from side to side as it moves”?
ATo support the claim that Jupiter’s gravity is strong enough to make lo’s orbit slightly noncircular
BTo argue against the claim that the bulge on lo‘s surface always points directly toward Jupiter
CTo illustrate a result of Europa’s gravitational effect on lo’s orbit
DTo provide evidence that lo behaves in a similar manner to the other Galilean moons
7
But lo Is not alone. As it orbits, it is constantly pulled by the gravity of its nearest large neighbor, another Galilean moon. Europa. Although Europa’s pull on lo is small. it is sufficient to make lo’s orbit slightly noncircular. In a noncircular orbit, the moons speed varies from place to place as it moves in its orbit around Jupiter but its rate of rotation on its axis remains constant. Thus it cannot keep the same face steadily turned toward Jupiter. Instead, as seen from Jupiter, lo turns slightly from side to side as it moves. On the other hand, the large tidal bulge on los surface caused by Jupiters gravity always points directly toward Jupiter, so it moves back and forth across lo’s surface as the moon wobbles. Those conflicting forces result in enormous tidal stresses that continually flex and squeeze lo’s interior.
According to paragraph 4, what is the effect of Europa’s gravity on lo?
AIt makes lo speed up or slow down during different parts of s orbit
BIt causes lo‘s rate of rotation on its axis to vary slightly as it moves around its orbit
CIt produces a gravitational bulge on lo
DIt is too small to significantly influence lo
8
Just as frequent back-and-forth bending of a piece of wire can produce heat through friction, the ever-changing distortion of lo’s interior constantly heats the moon. This generation of large amounts of heat within lo ultimately causes huge jets of gas and molten rock to squirt out of the moons surface. Galileos sensors indicated extremely high temperatures in the outflowing material. Researchers estimate that the total amount of heat generated within lo as a result of tidal flexing is about 100 million megawatts.
Which of the following can be inferred from paragraph 5 about the heat within Io?
AResearchers believe it to be well over 100 million megawatts
BIt Is generated by friction
CIt has been decreasing over time
DIt causes the moon’s entire surface to be molten
9
Of Jupite’s four largest moons, known as the Galilean moons, lo is the closest to Jupiter and the densest. ■ lo is the most geologically active object in the entire solar system. ■ In all, more than 80 active volcanoes have been identified on lo. ■ In contrast to the surfaces of he other Galilean moons, its surface is neither cratered nor streaked but is instead exceptionally smooth, mostly varying in altitude by less than one kilometer.■This smoothness is apparently the result of molten matter that constantly fills in any dents and cracks, giving lo the youngest surface of any known object in the solar system.
Look at the four squaresthat indicate where the following sentence could be added to the passage
Despite this, Io is further distinguished by being relatively featureless.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Io, one of Jupiter’s large Galilean moons, is the most geologically active object in the entire solar system.
AAll four of the Galilean moons have surfaces that are neither cratered nor streaked, indicating that they were either created relatively recently or have been protected from impacts.
BHeavy ions expelled by lo’s volcanoes create the lo plasma torus, a ing around Jupiter that can be detected from Earth.
CA large amount of heat is generated by the conflicting movements of Io and its gravitational bulge, and this heat is what causes the frequent volcanic eruptions on Io.
DJupiter’s magnetosphere is especially large due to the size of the planet, and it accelerates and heats all objects that come within it, from small particles to the large Galilean moons.
EThe moon Europa pulls on lo enough to prevent it from having a perfectly circular orbit, while Jupiters gravity creates a raised area on lo that always points toward the planet.
FSensors indicate that huge jets of gas and molten rock spew from Io’s surface, propelling and accelerating the Io plasma torus to high speeds.
