Rogue Planets
1 The formation of our solar system was highly chaotic: planet-sized objects formed from coalescing gas and dust and were destroyed in collisions, only to re-form later. Some of these objects fell into the Sun. Some orbited the Sun and became the planets we know today. Others were cast out of the solar system. Where are these worlds now? It’s unlikely that many of them would have a high enough velocity (speed) to escape from our galaxy. Therefore, they must still be out there, orbiting the galaxy center along with the Sun and other stars. These so-called rogue planets not only form in our solar system but in other planetary systems as well. Theorists surmise that the number of rogue planets might be anywhere between twice and thousands of times the number of conventional planets, which move in orbits around stars. Might any of them have enough heat to support living organisms?
2 The conditions on a rogue planet would depend on many factors. Computer models suggest, for example, that more than a dozen Mars-sized objects once orbited the inner solar system. It was, in fact, the collision of one of these with early Earth that led to the formation of our Moon. Because of its small mass, a Mars-sized rogue planet would quickly lose its heat and turn into a cold, dead world, with its atmosphere either having turned into a frozen layer on the ground or having escaped the gravity of the rogue planets.
3 On the other hand, a super-Earth (a planet two to ten times the mass of Earth), might meet a completely different fate. It would not necessarily lose its atmosphere, and it would have at least two important sources of energy: the leftover heat of formation and radioactivity. The first of these comes from the time when the rogue planet was still circling its star, sweeping up material during the early stages of the planetary system’s formation and heating up as a result of each collision. Once such heat has accumulated, it can take a long time to dissipate. Earth, for example, actually melted all the way through during its formation, and even today fully half the heat coming from its interior is a result of cooling down from that hot beginning. █ The other half of Earth’s interior heat comes from the radioactive decay of long-lived materials such as uranium. █ The key point is that once a planet has formed, both of these sources will continue to operate whether that planet continues to circle its star or is ejected into deep space. █
4 There is another factor that could make the surface of a rogue planet habitable, and that is a kind of modified greenhouse effect. █ On Earth, the greenhouse effect works like this: Sunlight comes through the atmosphere, which is transparent to optical (visible) wavelengths of light. The sunlight heats the surface of Earth, whose temperature causes it to emit infrared radiation—radiation whose wavelength is longer than that of visible light. This radiation is absorbed by atmospheric molecules like carbon dioxide and water vapor, which then reemit it. Some of this reemitted radiation continues out into space, but some is directed back toward Earth’s surface, where it is absorbed. The result is that the planet’s surface is at a higher temperature than it would be in the absence of this greenhouse effect. Without its naturally occurring greenhouse effect, in fact, Earth’s average temperature would be −18 degrees Celsius .
5 If you follow the details of this process, you realize that it doesn’t require incoming sunlight to operate. All that is needed is for the planet’s surface to have a source of heat, so that it emits infrared radiation. If it has enough surface heat and an atmosphere with enough greenhouse gases, you can imagine a rogue planet being a reasonable approximation of a world that is warm enough for water to exist and to support life. We can imagine scenarios in which primitive life developed in a rogue planet’s ocean, with lightning discharges or radioactivity instead of sunlight providing energy, but it is more likely that life-forms would originate at deep-sea vents—openings on the seafloor—feeding on materials and energy brought up from the planetary interior.
1
1 The formation of our solar system was highly chaotic: planet-sized objects formed from coalescing gas and dust and were destroyed in collisions, only to re-form later. Some of these objects fell into the Sun. Some orbited the Sun and became the planets we know today. Others were cast out of the solar system. Where are these worlds now? It’s unlikely that many of them would have a high enough velocity (speed) to escape from our galaxy. Therefore, they must still be out there, orbiting the galaxy center along with the Sun and other stars. These so-called rogue planets not only form in our solar system but in other planetary systems as well. Theorists surmise that the number of rogue planets might be anywhere between twice and thousands of times the number of conventional planets, which move in orbits around stars. Might any of them have enough heat to support living organisms?
According to paragraph 1, rogue planets differ from conventional planets in which of the following ways?
Rogue planets changed from orbiting a star to orbiting the center of the galaxy.
Rogue planets are rarely found outside our solar system.
Most rogue planets have escaped our galaxy.
Rogue planets formed earlier than most planetary systems did.
2
2 The conditions on a rogue planet would depend on many factors. Computer models suggest, for example, that more than a dozen Mars-sized objects once orbited the inner solar system. It was, in fact, the collision of one of these with early Earth that led to the formation of our Moon. Because of its small mass, a Mars-sized rogue planet would quickly lose its heat and turn into a cold, dead world, with its atmosphere either having turned into a frozen layer on the ground or having escaped the gravity of the rogue planets.
Which of the following can be inferred from paragraph 2 about the Mars-sized rogue planets that once orbited the inner solar system?
The conditions that exist on them are typical of the conditions on rogue planets in general.
Some of them are still in the inner solar system.
Some of them may have moons orbiting around them.
They would have all become too cold to be habitable by living organisms.
3
3 On the other hand, a super-Earth (a planet two to ten times the mass of Earth), might meet a completely different fate. It would not necessarily lose its atmosphere, and it would have at least two important sources of energy: the leftover heat of formation and radioactivity. The first of these comes from the time when the rogue planet was still circling its star, sweeping up material during the early stages of the planetary system’s formation and heating up as a result of each collision. Once such heat has accumulated, it can take a long time to dissipate. Earth, for example, actually melted all the way through during its formation, and even today fully half the heat coming from its interior is a result of cooling down from that hot beginning. █ The other half of Earth’s interior heat comes from the radioactive decay of long-lived materials such as uranium. █ The key point is that once a planet has formed, both of these sources will continue to operate whether that planet continues to circle its star or is ejected into deep space. █
The word “ leftover ” in the passage is closest in meaning to
intense
stored
remaining
spreading
4
3 On the other hand, a super-Earth (a planet two to ten times the mass of Earth), might meet a completely different fate. It would not necessarily lose its atmosphere, and it would have at least two important sources of energy: the leftover heat of formation and radioactivity. The first of these comes from the time when the rogue planet was still circling its star, sweeping up material during the early stages of the planetary system’s formation and heating up as a result of each collision. Once such heat has accumulated, it can take a long time to dissipate. Earth, for example, actually melted all the way through during its formation, and even today fully half the heat coming from its interior is a result of cooling down from that hot beginning. █ The other half of Earth’s interior heat comes from the radioactive decay of long-lived materials such as uranium. █ The key point is that once a planet has formed, both of these sources will continue to operate whether that planet continues to circle its star or is ejected into deep space. █
According to paragraph 3, which of the following is the main cause of Earth’s complete melting during its formation?
The loss of its atmosphere
The resistance against being ejected into deep space
The accumulation of heat from collisions while circling its star
The buildup of radioactive materials in its interior
5
4 There is another factor that could make the surface of a rogue planet habitable, and that is a kind of modified greenhouse effect. █ On Earth, the greenhouse effect works like this: Sunlight comes through the atmosphere, which is transparent to optical (visible) wavelengths of light. The sunlight heats the surface of Earth, whose temperature causes it to emit infrared radiation—radiation whose wavelength is longer than that of visible light. This radiation is absorbed by atmospheric molecules like carbon dioxide and water vapor, which then reemit it. Some of this reemitted radiation continues out into space, but some is directed back toward Earth’s surface, where it is absorbed. The result is that the planet’s surface is at a higher temperature than it would be in the absence of this greenhouse effect. Without its naturally occurring greenhouse effect, in fact, Earth’s average temperature would be −18 degrees Celsius .
The word “ modified ” in the passage is closest in meaning to
altered
extended
increased
controlled
6
4 There is another factor that could make the surface of a rogue planet habitable, and that is a kind of modified greenhouse effect. █ On Earth, the greenhouse effect works like this: Sunlight comes through the atmosphere, which is transparent to optical (visible) wavelengths of light. The sunlight heats the surface of Earth, whose temperature causes it to emit infrared radiation—radiation whose wavelength is longer than that of visible light. This radiation is absorbed by atmospheric molecules like carbon dioxide and water vapor, which then reemit it. Some of this reemitted radiation continues out into space, but some is directed back toward Earth’s surface, where it is absorbed. The result is that the planet’s surface is at a higher temperature than it would be in the absence of this greenhouse effect. Without its naturally occurring greenhouse effect, in fact, Earth’s average temperature would be −18 degrees Celsius .
What is the author’s purpose in explaining that “ Without its naturally occurring greenhouse effect, in fact, Earth’s average temperature would be −18 degrees Celsius ”?
To point out the importance of sunlight as Earth’s source of heat
To emphasize the importance of the greenhouse effect in making Earth habitable
To demonstrate the relationship between infrared radiation and various molecules in Earth’s atmosphere To contrast Earth’s sources of heat with the sources of heat for rogue planets
7
Paragraph 4 mentions all of the following as part of the greenhouse effect process on Earth EXCEPT:
Solar radiation comes through the atmosphere and warms Earth’s surface.
Visible light is emitted from Earth’s surface back into the atmosphere.
Infrared radiation is absorbed by atmospheric molecules and reemitted.
Some of the reemitted radiation is absorbed back into Earth’s surface.
8
5 If you follow the details of this process, you realize that it doesn’t require incoming sunlight to operate. All that is needed is for the planet’s surface to have a source of heat, so that it emits infrared radiation. If it has enough surface heat and an atmosphere with enough greenhouse gases, you can imagine a rogue planet being a reasonable approximation of a world that is warm enough for water to exist and to support life. We can imagine scenarios in which primitive life developed in a rogue planet’s ocean, with lightning discharges or radioactivity instead of sunlight providing energy, but it is more likely that life-forms would originate at deep-sea vents—openings on the seafloor—feeding on materials and energy brought up from the planetary interior.
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.
It is possible that life-forms developed in a rogue planet’s ocean with sunlight providing energy, but they would also likely have needed to feed on materials and energy that came from the planetary interior.
It is possible that life-forms developed in a rogue planet’s ocean with energy from lightning or radioactivity, but it is more likely that they originated at deep-sea vents with energy from the planetary interior.
We can imagine that energy sources on a rogue planet included lightning discharges, radioactivity, and sunlight, without which life would not likely originate at deep-sea vents.
We can imagine an ocean on a rogue planet with lightning or radioactivity, but for life to develop, it is more likely that the ocean received energy from sunlight or from deep-sea vents.
9
3 On the other hand, a super-Earth (a planet two to ten times the mass of Earth), might meet a completely different fate. It would not necessarily lose its atmosphere, and it would have at least two important sources of energy: the leftover heat of formation and radioactivity. The first of these comes from the time when the rogue planet was still circling its star, sweeping up material during the early stages of the planetary system’s formation and heating up as a result of each collision. Once such heat has accumulated, it can take a long time to dissipate. Earth, for example, actually melted all the way through during its formation, and even
today fully half the heat coming from its interior is a result of cooling down from that hot beginning. █ The other half of Earth’s interior heat comes from the radioactive decay of long-lived materials such as uranium. █ The key point is that once a planet has formed, both of these sources will continue to operate whether that planet continues to circle its star or is ejected into deep space. █
4 There is another factor that could make the surface of a rogue planet habitable, and that is a kind of modified greenhouse effect. █ On Earth, the greenhouse effect works like this: Sunlight comes through the atmosphere, which is transparent to optical (visible) wavelengths of light. The sunlight heats the surface of Earth, whose temperature causes it to emit infrared radiation—radiation whose wavelength is longer than that of visible light. This radiation is absorbed by atmospheric molecules like carbon dioxide and water vapor, which then reemit it. Some of this reemitted radiation continues out into space, but some is directed back toward Earth’s surface, where it is absorbed. The result is that the planet’s surface is at a higher temperature than it would be in the absence of this greenhouse effect. Without its naturally occurring greenhouse effect, in fact, Earth’s average temperature would be −18 degrees Celsius .
Thus, a rogue planet could have enough heat to support life.
Where would the sentence best fit? Click on a square [█] to add the sentence to the passage.
10
There are numerous rogue planets in our galaxy.
A Mars-sized rogue planet reentered the solar system and collided with early Earth, causing the formation of our Moon.
It is possible that some rogue planets are receiving radiation of various wavelengths from distant stars while orbiting the galaxy center.
Because even the largest rogue planets lack greenhouse gases to warm them, their surfaces would likely be very cold.
Rogue planets with small masses would have lost their heat and become cold, dark worlds without atmospheres.
Larger-sized rogue planets might still contain a source of heat from the early stages of their formation or from the ongoing radioactive decay in their interiors.
It is possible that some rogue planets with greenhouse gases may have enough surface heat for life to develop on the seafloor.
