Astronomy 101 Exam 3
|Which of the following statements about our Sun is NOT true?|
-The Sun is a star.
|-The Sun’s diameter is about five times that of Earth.|
|The planet in our solar system with the highest average surface temperature is __________.|
|Which jovian planet does NOT have rings?|
|-All the jovian planets have rings.|
|What is the Kuiper belt?|
-a technical name for the asteroid belt
|-a region of the solar system beginning just beyond the orbit of Neptune that contains many icy comets|
|Which of the following statements about Pluto is true?|
-It is the largest known object that is considered to be a dwarf planet.
|-It has more in common with comets in the Kuiper belt than it does with terrestrial planets like Earth.|
|Suppose you view the solar system from high above Earth’s North Pole. Which of the following statements about planetary orbits will be true?|
-The inner planets orbit the Sun counterclockwise while the outer planets orbit the Sun clockwise.
|-All the planets orbit counterclockwise around the Sun.|
|When we say that jovian planets contain significant amounts of hydrogen compounds, we mean all the following chemicals EXCEPT ______.|
|What is the Kuiper belt?|
-a region of the solar system that extends almost a fourth of the way to the nearest stars and contains a trillion comets with orbits going in all directions around the Sun
|-a region of the solar system beginning just beyond the orbit of Neptune that contains many icy comets|
|What is the Oort cloud?|
-It is a great cloud of gas that resides far beyond the orbit of Pluto.
|-It’s not really a cloud at all, but rather refers to the trillion or so comets thought to orbit the Sun at great distances.|
|In essence, the nebular theory holds that _________.|
-our solar system formed from the collapse of an interstellar cloud of gas and dust
|-our solar system formed from the collapse of an interstellar cloud of gas and dust|
|What do we mean by the frost line when we discuss the formation of planets in the solar nebula?|
-It marks the special distance from the Sun at which hydrogen compounds become abundant; closer to the Sun, there are no hydrogen compounds.
|-It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.|
|According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?|
-Its mass, temperature, and density all increased.
|-It got hotter, its rate of rotation increased, and it flattened into a disk.|
|What is the giant impact hypothesis for the origin of the Moon?|
-The Moon originally was about the same size as Earth, but a giant impact blasted most of it away so that it ended up much smaller than Earth.
|-The Moon formed from material blasted out of Earth’s mantle and crust by the impact of a Mars-size object.|
|According to modern scientific dating techniques, approximately how old is the solar system?|
-4.5 billion years
|-4.5 billion years|
|Which of the following types of material can condense into what we call ice at low temperatures?|
|According to our theory of solar system formation, what are asteroids and comets?|
-chunks of rock or ice that condensed after the planets and moons finished forming
|-leftover planetesimals that never accreted into planets|
|Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass?|
-You’ll have 0.5 kilogram of the radioactive substance remaining.
|-You’ll have 0.25 kilogram of the radioactive substance remaining.|
|Our Moon is about the same size as moons of the other terrestrial planets.|
True or false?
|On average, Venus is the hottest planet in the solar system – even hotter than Mercury.|
True or False?
|What’s unusual about our Moon?|
-It’s the only moon that orbits a terrestrial planet.
|-It’s surprisingly large relative to the planet it orbits.|
|Based on your study of the Interactive Figure, which of the following is not one of the four major features of the solar system?|
-Several exceptions to the general trends stand out.
|-The solar system contains eight planets plus dwarf planets (including Ceres, Pluto, and Eris).|
*The precise number of planets is not thought to be of any particular significance, and the division between “planets” and “dwarf planets” is a recent classification scheme that does not affect the basic ideas in the four major features. That is, for the purposes of the four major features, the dwarf planets are considered to be equivalent to large asteroids or comets.*
|Study the features relating to the first characteristic (orderly motions); click on the inner or outer solar system to see the planets in motion, then scroll over the planets to see diagrams of their axis tilts. Which of the following correctly describe patterns of motion in the solar system?|
Check all that apply.
-The inner planets all rotate in the same direction (west to east) as Earth.
|-Planets closer to the Sun move around their orbits at higher speed than planets farther from the Sun.|
-All the planets (not counting Pluto) orbit the Sun in nearly the same plane.
-All the planets (not counting Pluto) have nearly circular orbits.
|Now consider the second major characteristic (two types of planets). Which of the following statements are true?|
Check all that apply.
-Jovian planets have more moons than terrestrial planets.
|-Jovian planets have more moons than terrestrial planets.|
-Jovian planets are larger in size than terrestrial planets.
-Jovian planets are larger in mass than terrestrial planets.
-Jovian planets orbit farther from the Sun than terrestrial planets.
|The solar system contains vast numbers of small bodies, which we call asteroids when they are rocky and comets when they are icy. These small bodies are concentrated in the region(s) of the solar system that we call __________.|
Check all that apply.
-the Kuiper belt
|-the Kuiper belt|
-the asteroid belt
-the Oort cloud
|All the following statements are true. Which of them are considered to be “exceptions” to the general trends described by the first three major characteristics of the solar system?|
Check all that apply.
-Our Moon has a diameter more than 1/4 the diameter of Earth.
|-Our Moon has a diameter more than 1/4 the diameter of Earth.|
-Venus rotates in a direction opposite to the rotation of the other terrestrial planets.
-Uranus rotates with an axis tilt that lies nearly in the ecliptic plane.
|Consider only the observed patterns of motion in the solar system. Scientifically, which of the following possible conclusions is justified from the patterns of motion alone?|
-The planets were born from a giant cloud of gas that rotated in the same direction that the Milky Way Galaxy rotates.
|-The planets were not each born in a separate, random event.|
|Now consider why the observed patterns of motion lead to the conclusion that the planets were not born in separate, random events. The reason for this conclusion is that, if the planets had been born in separate, random events, we would expect that __________.|
-planets would orbit at much higher speeds than they actually do
|-planetary orbits would have many different orientations and directions, rather than all being in the same direction and in the same plane|
*In science, we form hypotheses to explain something, then use the hypotheses to make predictions that we can test. In this case, we have two alternate hypotheses: random births or birth from a single cloud of gas. The hypothesis of random births predicts random orbits, which does not agree with reality and therefore has been discarded. The hypothesis of birth from a single cloud predicts patterns of motion that match those we observe; this match of prediction and observation provides evidence in favor of the hypothesis.*
|Today, scientists have a theory (the nebular theory) that explains all the major characteristics of the solar system. In science, we expect a theory like this not only to explain the observed characteristics of our solar system but also to __________.|
-predict some major change that will eventually occur in our own solar system
|-make testable predictions about other solar systems|
*A scientific theory must always make testable predictions, because that is the only way we can evaluate the validity of the theory.*
|Listed following are characteristics that can identify a planet as either terrestrial or jovian. Match these to the appropriate category.||Terrestrial Planets:|
-solid, rocky surface
-located within the inner solar system
|The following images show six objects in our solar system. Rank the objects from left to right based on their average distance from the Sun, from farthest to closest. (Not to scale.)||Farthest:|
|The following images show six objects in our solar system. Rank these objects from left to right based on their mass, from highest to lowest. (Not to scale.)||Highest Mass:|
|The images below show six objects in our solar system. Rank these objects by size (average equatorial radius), from largest to smallest. (Not to scale.)||Largest radius:|
|The following images show five planets in our solar system. Rank these planets from left to right based on their average surface (or cloud-top) temperature, from highest to lowest. (Not to scale.)||Highest Temperature:|
*Notice that, for these five planets, temperature correlates with distance from the Sun: the closer to the Sun, the hotter the planet. Remember, however, that this is not always the case, because a planet’s temperature also depends on its reflectivity and on the strength of its greenhouse effect (if any). For example, the greenhouse effect gives Venus a higher average temperature than Mercury, even though Venus is nearly twice as far from the Sun.*
|The following images show five planets in our solar system. Rank these planets from left to right based on the amount of time it takes them to orbit the Sun, from longest to shortest. (Not to scale.)||Longest Time:|
*Recall that the time it takes a planet to orbit the Sun is called its orbital period, and that Kepler’s third law tells us that orbital period increases with distance from the Sun. That is why the ranking order for orbital period is the same as the ranking order for distance from the Sun.*
|The following images show four planets in our solar system. Rank these planets from left to right based on the number of moons that orbit them, from highest to lowest. (Not to scale.)||Highest Number:|
*Jupiter has many moons as a consequence of its formation, in which moons formed in a disk of material surrounding it and its extended atmosphere at the time allowed it to capture numerous small bodies into orbit. Mars has two very small moons that it presumably captured at a time when it, too, had an extended atmosphere. Earth’s single but surprisingly large moon is thought to have formed as a result of a giant impact. Mercury (and Venus) have no moons.*
|The mass of the Sun compared to the mass of all the planets combined is like the mass of an elephant compared to the mass of a cat.|
True or False?
|The weather conditions on Mars today are much different than they were in the distant past.|
True or False?
|Moons cannot have atmospheres, active volcanoes, or liquid water.|
True or False?
|Saturn is the only planet in the solar system with rings.|
True or False?
|Which terrestrial planets have had volcanic activity at some point in their histories?|
|-all of them|
|Large moons orbit their planets in the same direction the planet rotates:|
-half of the time.
|-most of the time.|
|Pluto orbits the Sun in the opposite direction of all the other planets.|
True or False?
|How many of the planets orbit the Sun in the same direction that Earth does?|
|What fraction of the moons of the planets orbit in the same direction that their planets rotate?|
|Observations show that interstellar clouds can have almost any shape and, if they are rotating at all, their rotation is not perceptible. However, as shown in the animation, the nebular theory predicts that a cloud will rotate rapidly once it shrinks to a small size. What physical law explains why a cloud will rotate rapidly as it collapses?|
-the law of conservation of energy
|-the law of conservation of angular momentum|
*The law of conservation of angular momentum holds because the cloud is collapsing only due to gravity. Because angular momentum is proportional to velocity times radius, keeping this product constant requires that the velocity of rotation increase when the cloud radius decreases.*
|The nebular theory also predicts that the cloud should heat up as it collapses. What physical law explains why it heats up?|
-Kepler’s second law
|-the law of conservation of energy|
*The law of conservation of energy tells us that energy must always be conserved. Because the cloud has much more gravitational potential energy when it is large in size than when it is small, its gravitational potential energy must be transformed into other forms of energy, such as heat (thermal energy), as it shrinks in size.*
|The nebular theory also predicts that the cloud will flatten into a disk as it shrinks in size. Which of the following best explains why the collapsing cloud should form a disk?|
-As a star forms near the cloud center, its wind blows away material that is not aligned with its equator, thereby leaving an equatorial disk of material.
|-Colliding cloud particles exchange angular momentum and, on average, end up with the rotation pattern for the cloud as a whole.|
*Particles in the collapsing cloud inevitably collide with one another. These collisions allow particles to exchange angular momentum, but their total angular momentum must be conserved. Therefore, many collisions result in an averaging out of the angular momentums of individual cloud particles, a process that brings their orbits into approximately the same plane.*
|As you’ve seen, the nebular theory predicts that a cloud that gives birth to planets should have the shape of a spinning disk. Which observable property of our solar system supports this prediction?|
-There are two basic types of planets: terrestrial and jovian.
|-All the planets orbit the Sun in the same direction and in nearly the same plane.|
*The orbits of the planets thereby reflect the rotation pattern of the flat, rotating disk in which they formed*
|The solar system has two types of planets, terrestrial and jovian. According to the nebular theory, why did terrestrial planets form in the inner solar system and jovian planets in the outer solar system?|
-All the planets started out large, but the Sun’s heat evaporated so much material that the inner planets ended up much smaller.
|-Ices condensed only in the outer solar system, where some icy planetesimals grew large enough to attract gas from the nebula, while only metal and rock condensed in the inner solar system, making terrestrial planets.|
*Only metal and rock could condense at the high temperature of the inner solar system, so the inner planets were built by the accretion of metal and rock. Farther out, ices could also condense, leading to the accretion of ice-rich planetesimals. Some of these grew large enough for their gravity to attract gas from the solar nebula and become jovian planets.*
|Based on the nebular theory as it explains our own solar system, which of the following should we expect to be true for other star systems?|
Check all that apply.
-Planetary systems should generally have all planets orbiting in nearly the same plane.
|-Planetary systems should generally have all planets orbiting in nearly the same plane.|
-Planetary systems should be common.
-Jovian planets always form farther from their star than terrestrial planets.
-Other planetary systems should have the same two types of planets: terrestrial and jovian.
*We expect all solar systems to form in similar ways and therefore to share the basic features, such as planets all orbiting in the same direction and nearly the same plane and having two basic types of planets that form in different regions. However, we do not expect particulars that are probably coincidental, such as the precise numbers of planets, to be the same in different solar systems.*
|Listed following are statements that, based on our current theory of solar system formation, apply either to the formation of terrestrial planets or of jovian planets, but not both. Match these to the appropriate category.||Terrestrial Planets:|
-Surfaces dramatically altered during the heavy bombardment
-Accreted from planetesimals of rock and metal
|What is Jupiter’s main ingredient?|
-rock and metal
|-hydrogen and helium|
|Which lists the major steps of solar system formation in the correct order?|
-collapse, accretion, condensation
|-collapse, condensation, accretion|
|Leftover ice-rich planetesimals are called:|
|Why didn’t a terrestrial planet form at the location of the asteroid belt?|
-There was never enough material in that part of the solar nebula.
|-Jupiter’s gravity kept planetesimals from accreting.|
|The materials that made up the solar nebula can be categorized into the four general types as follows. Rank these materials from left to right based on their abundance in the solar nebula, from highest to lowest.||Highest Abundance:|
Hydrogen and Helium Gas
*Knowing this ranking order is useful, but even more important is to recognize the vast differences in abundance: Hydrogen and helium gas constituted about 98 percent of the mass in the solar nebula. Most of the rest was hydrogen compounds, which were nearly three times as abundant as rock and metal combined.*
|The materials that made up the solar nebula can be categorized into these four general types. Rank these materials from left to right based on the temperature at which each would condense into a solid, from highest to lowest. Note: For a substance that does not condense at all, rank it as very low temperature.||Highest Temperature:|
Hydrogen and Helium Gas
*In fact, hydrogen and helium gas never condense into solid form under the conditions that exist in interstellar clouds such as the solar nebula. Continue on to Part C to see how the condensation temperatures of the other materials explain why different materials condensed in different regions of the young solar system.*
|As you’ve learned from Part B, hydrogen and helium gas never condense under conditions found in the solar nebula. The remaining three categories of material in the solar nebula are shown again here. Rank these materials from left to right based on the distance from the Sun at which they could condense into a solid in the solar nebula, from farthest to closest.||Farthest:|
*These condensation regions explain the makeup of objects at different distances from the Sun. In the inner regions of the solar nebula, where temperatures were high, only metal and rock could condense, which is why the inner planets ended up being made of metal and rock. Farther out, hydrogen compounds could condense into ices, which is why comets and outer solar system moons contain large amounts of ice. And because hydrogen compounds are more abundant than metal or rock, some of the solid objects in the outer solar system grew so large that their gravity could pull in hydrogen and helium gas, which explains how the jovian planets formed*
|What substances were found within the inner 0.3 AU of the solar system before planets began to form?|
-nothing at all
|-rocks, metals, hydrogen compounds, hydrogen, and helium, all in gaseous form|
*You will see that all the materials of the solar nebula were present in the inner region, but it was too hot for any of them to condense. As a result, they were all in gaseous form.*
|What substances existed as solid flakes within the inner 0.3 AU of the solar system before planets began to form?|
*Although all the materials were present in gaseous form, the inner 0.3 AU of the newly forming solar system was too warm for even rocks or metals to condense into solid flakes.*
|Where would you expect terrestrial planets to form in the solar nebula?|
-within the inner 0.3 AU
|-anywhere between 0.3 AU and the frost line|
*Terrestrial planets are made mostly of metal and rock and therefore formed in the region in which it was cool enough for metal and rock to condense but still too warm for hydrogen compounds to condense into ices. This means the region between the rock/metal condensation line at 0.3 AU and the frost line.*
|The jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetesimals made of __________.|
-only rocks and metals
|-rocks, metals, and ices|
*Because ices could condense only beyond the frost line, we expect jovian planets to form only beyond the frost line. Note that many extrasolar planets appear to be jovian but are located close to their stars, leading scientists to suspect that these planets migrated inward after originally forming beyond the frost lines of their star systems.*
|Provided following are stages that occurred during the formation of our solar system. Rank these stages from left to right based on when they occurred, from first to last.||First Stage:|
Large Cloud of Gas and Dust
Contraction of Solar Nebula
Condensation of Solid Particles
Accretion of Planetesimals
Clearing the Solar Nebula
*Once the solar wind helped clear away the remaining gas in the solar nebula, the era of planet formation was essentially over. Remember that all these stages occurred over a period of millions of years, ending about 4 1/2 billion years ago.*
To understand how observational evidence is used to test the nebular theory.
Introduction. Our modern theory of the formation of our solar system, called the nebular theory, successfully explains all the major features of our solar system. In this tutorial, you will consider how this theory should apply to other solar systems.
Sort the following hypothetical discoveries into the appropriate bins as follows:
Consistent with theory: The statement describes a discovery that we could reasonably expect to find if the nebular theory is correct.
Not consistent with theory: The statement describes a discovery that would force us to modify or discard the nebular theory.
|Consistent with Theory:|
-A star is surrounded by a disk of gas but has no planets.
-A star has 20 planets.
-Of a star’s 5 terrestrial planets, 1 has a moon as large as Earth’s moon.
-Beyond its jovian planets, star has two ice-rich objects as large as Mars.
Not Consistent with Theory:
|Two hypothetical discoveries in Part A deal with moons that, like Earth’s moon, are relatively large compared to their planets. Which of the following best explains why finding 1 planet with such a moon is consistent with the nebular theory, while finding 6 planets with such moons is not consistent?|
-The nebular theory holds that moons of any size should be rare, so finding 1 is not too surprising but finding 6 would be very surprising.
-The nebular theory says that only planets at least as large as Earth can have large Moons, and 6 Earth-size planets would not be likely to form in one solar system.
-Unusually large moons form in giant impacts, which are relatively rare events.
|-Unusually large moons form in giant impacts, which are relatively rare events.|
*Our Moon is thought to have formed as a result of a giant impact in which a Mars-size object slammed into the young Earth. The fact that this happened to 1 of the 4 terrestrial planets in our solar system suggests that it is reasonable to find the same thing on a similar fraction of the terrestrial planets in another system. But it would be very surprising to find it happening to 6 out of 6 terrestrial planets.*
|Consider the hypothetical discovery from Part A reading: “A star’s 5 terrestrial planets orbit in the opposite direction of its 3 jovian planets.” This discovery would be inconsistent with the nebular theory because the theory holds that __________.|
-star systems should have equal numbers of terrestrial and jovian planets
|-all the planets formed in a rotating, disk-shaped nebula|
*The nebular theory predicts that all planets should be born on orbits going in the same direction and in nearly the same plane.*
|Consider the hypothetical discovery from Part A reading: “Beyond its jovian planets, a star has two ice-rich objects as large as Mars.” This discovery is consistent with the nebular theory, because this theory predicts that _________.|
-terrestrial planets sometimes form beyond the jovian planets
|-this might have happened in our own solar system if it had taken longer for the solar wind to clear the solar nebula|
*If the solar nebula had remained for a longer time, accretion could have continued for a longer period of time, forming larger ice-rich objects. In fact, we cannot yet be sure that this didn’t happen in our solar system: Eris, which is slightly larger than Pluto, was discovered only in 2005, and it’s possible that even larger ice-rich objects remain to be discovered.*
|What’s the leading theory for the origin of the Moon?|
-It formed along with Earth.
|-It formed from the material ejected from Earth in a giant impact|
|About how old is the solar system?|
-4.5 million years
|-4.5 billion years|
|Assuming that other planetary systems form in the same way as our solar system formed, where would you expect to find terrestrial planets?|
-Terrestrial planets will likely be located farther from the planetary system’s star than any jovian planets.
|-Terrestrial planets will likely be located nearer the planetary system’s star than any jovian planets.|
*Based on what we find in our own solar system, we expect terrestrial planets to form close to a star and jovian planets to form farther out.*
|Compared to terrestrial planets, jovian planets are __________.|
-more massive and higher in average density
|-more massive and lower in average density|
*Note that while jovian planets are lower in average density than terrestrial planets, the densities in their deep interiors are quite high, in some cases higher than the densities found at the centers of the terrestrial worlds.*
|Which planet is approximately halfway between Pluto’s orbit and the Sun?|
-Mars, the fourth planet from the Sun
|-Uranus, the seventh planet from the Sun|
*Notice that Uranus is located at an average distance of 19.2 AU, which is close to half of Pluto’s average distance of 39.5 AU. Many people are surprised to realize that Uranus, the seventh planet from the Sun, is only half as far as Pluto. As you can see in the figure, this surprising fact arises because the outer planets are much more widely spaced than the inner planets.*
|The dwarf planet Eris was discovered in 2005, orbiting the Sun at an average distance about twice that of Pluto. In which of the following ways do Pluto and Eris differ from the terrestrial and jovian planets in our solar system?|
Check all that apply.
-Both Pluto and Eris are smaller than any of the terrestrial planets.
|-Both Pluto and Eris are smaller than any of the terrestrial planets.|
-Both Pluto and Eris travel in more elliptical orbits than any of the terrestrial or jovian planets.
-Both Pluto and Eris are less massive than any of the terrestrial or jovian planets.
|1. _________________ is about 30 times as far from the Sun as our own planet.||Neptune|
|2. _______________ is the planet with the highest average surface temperature.||Venus|
|3. The planet with the lowest average density is ____________________.||Saturn|
|4. The planet that orbits closest to the Sun is ___________________.||Mercury|
|5. The only rocky planet to have more than one moon is _______________.||Mars|
|6. __________________ is the jovian planet that orbits closest to the Sun.||Jupiter|
|7. _______________ has a rotational axis that is tilted so much it lies nearly in the plane of its orbit.||Uranus|
|8. Most of the surface of _____________ is covered with liquid water.||Earth|
|Which of the following is not a major pattern of motion in the solar system?|
-The Sun and most of the planets rotate in the same direction in which the planets orbit the Sun.
|-Nearly all comets orbit the Sun in same direction and roughly the same plane.|
*This statement is untrue because comets of the Oort cloud, which are the most numerous of all comets, have randomly oriented orbits going in all directions around the Sun*
|Which of the following is not a major difference between the terrestrial and jovian planets in our solar system?|
-Terrestrial planets contain large quantities of ice and jovian planets do not.
|-Terrestrial planets contain large quantities of ice and jovian planets do not.|
*Terrestrial planets actually contain very little ice, because they are made mostly of metal and rock.*
|Consider the following statement: “Rocky asteroids are found primarily in the asteroid belt and Kuiper belt while icy comets are found primarily in the Oort cloud.” What’s wrong with this statement?|
-The Oort cloud has nothing to do with comets.
|-The Kuiper belt contains icy comets, not rocky asteroids.|
*The Kuiper belt consists of material that accreted far beyond the frost line, and hence its objects are icy in composition – making them comets.*
|Which of the following is not a real difference between asteroids and comets?|
-Asteroids are made mostly of rock and comets are made mostly of ice.
|-Asteroids orbit the Sun while comets just float randomly around in the Oort cloud.|
*Comets also orbit the Sun, although their orbital periods can be many thousands or millions of years. Indeed, just “floating randomly” is not possible for an object under the influence of the Sun’s gravity – any such object must follow one of the orbits allowed by the law of gravity (see Chapter 4).*
|The following statements are all true. Which one counts as an “exception to the rule” in being unusual for our solar system?|
-Venus does not have a moon.
|-The diameter of Earth’s Moon is about 1/4 that of Earth.|
|Compared to the distance between Earth and Mars, the distance between Jupiter and Saturn is ______.|
-just slightly less
|How is Einstein’s famous equation, E=mc 2, important in understanding the Sun?|
-It explains why the Sun has a magnetic field strong enough influence the atmospheres of the planets.
|-It explains the fact that the Sun generates energy to shine by losing some 4 million tons of mass each second.|
*The “lost” 4 million tons is converted to an amount of energy equal to this mass times the speed of light squared. Note that although 4 million tons per second sounds like a lot, it is quite small compared to the Sun’s total mass.*
|Venus has a higher average surface temperature than Mercury. Why?|
-Because it is closer to the Sun.
|-Because its surface is heated by an extreme greenhouse effect.|
*It is the same type of greenhouse effect that warms Earth, but Venus has so much carbon dioxide in its atmosphere that the greenhouse effect is far stronger than on Earth.*
|In what way is Venus most similar to Earth?|
-Both planets are nearly the same size.
|-Both planets are nearly the same size.|
*This similarity in size means the two planets are probably quite similar in their interior structures and fundamental properties, though they have obvious and important differences on their surfaces.*
|Which of the following statements about the object called Eris is not true?|
-It is thought to be the first example of a new class of object.
|-It is thought to be the first example of a new class of object.|
|Mars has two moons that are most similar in character to:|
*Indeed, these moons are probably asteroids that Mars captured into orbit long ago.*
|Imagine that an alien spaceship crashed onto Earth. Which statement would most likely be true?|
-The crash would create a noticeable crater.
|-It would crash in the ocean.|
*This is very likely, because Earth’s surface is about 3/4 covered by oceans.*
|Which planet listed below has the most extreme seasons?|
*Remember that seasons are caused primarily by axis tilt. Uranus essentially rotates on its side compared to its orbit, giving it very extreme seasons.*
|In what way is Pluto more like a comet than a planet?|
-It has a long tail.
|-It is made mostly of rock and ice.|
*In other words, Pluto’s composition is nearly identical to the composition of most comets.*
|Why was it advantageous for the Voyager mission to consist of flybys rather than orbiters?|
-Flyby spacecraft can get closer to a planet than an orbiting spacecraft.
|-Each individual spacecraft was able to visit more than one planet.|
*Voyager 1 visited Jupiter and Saturn, and Voyager 2 visited all four jovian planets.*
|Why has NASA sent recent orbiters to Mars (such as Mars Reconnaissance Orbiter) on trajectories that required them to skim through Mars’s atmosphere before settling into their final orbits?|
-It allowed the spacecraft to collect samples of the atmospheric gas for return to Earth.
|-Mars||This photograph was taken on the surface of another world in our solar system. What world is it?|
|Which pair of photos below shows Earth correctly scaled in comparison to the Sun?|
|-Saturn, because of its colors and bright, wide rings.||What planet is this, and how do you know?|
-Neptune, because it has the brightest rings of any planet.
|Which pair of photos below shows Earth correctly scaled in comparison to Jupiter?||*Jupiter’s diameter is about 11 times that of Earth, so about 11 Earth’s could fit across Jupiter’s equator.*|
|-a comet||In this photograph, the large and bright object in the sky is:|
|-Earth as viewed from the outskirts of the solar system.||This famous photograph taken by the Voyager spacecraft shows _________.|
-Earth as viewed from the outskirts of the solar system.
|-exaggerated about a million times||In this perspective view of the solar system, the sizes of the planets are ___________ relative to the sizes of their orbits.|
-exaggerated about a million times
|-an asteroid||This photo shows ___________.|
|-Neptune||What do we see in this photo?|
|-Mars||What planet is shown in this photo?|
|1. The first few hundred million years of the solar system 19s history were the time of the _______________________________ , during which Earth suffered many large impacts.||heavy bombardment|
|2. The era of planet formation ended when the remaining hydrogen and helium gas of the solar nebula was swept into interstellar space by the ________________________.||solar wind|
|3. Ice can form from a gas through the process of ________________________.||condensation|
|4. Hydrogen compounds in the solar system can condense into ices only beyond the _______________________.||frost line|
|5. Our Moon was most likely formed by a collision between Earth and a Mars-sized _______________________.||planetesimal|
|6. Mars was formed by the _______________ of smaller objects.||accretion|
|7. Our solar system was created by the gravitational collapse of the _________________.||solar nebula|
|8. _________________________ allows us to determine the age of a solid rock.||radiometric dating|
|-an interstellar cloud that will ultimately give birth to thousands of star systems|
*This particular cloud is the Orion Nebula. (This photo is a composite made from both infrared and visible light.*
|What does this photo show?|
-a galaxy much like our Milky Way Galaxy
|-It shows that stars really can be surrounded by flattened disks of dust and gas.||This photo shows a “debris disk” around a nearby star. What is the significance of this type of “debris disk”?|
-It shows that the disks that encircle stars are sometimes split into two pieces, with one on each side of the star.
|-the law of conservation of angular momentum|
*The cloud rotates very slowly when it is large, but as it shrinks it must rotate faster to keep its angular momentum conserved, much like a skater pulling in her arms as she spins.*
|This sequence of paintings shows how a large gas cloud can collapse to become a much smaller, spinning disk of gas. What law explains why cloud spins faster as it shrinks in size?|
-the universal law of gravitation
|-the law of conservation of energy|
*The cloud has a lot of gravitational potential energy when it is large, and this energy becomes thermal energy as the cloud collapses.*
|This sequence of paintings shows how a large gas cloud can collapse to become a much smaller, spinning disk of gas. What law explains why the center of the cloud becomes so much hotter as the cloud shrinks in size?|
-Newton’s second law of motion
*Rock and metal could condense throughout most of the solar nebula, but ice could condense only beyond the frost line. Therefore, objects that contain all three ingredients must have formed beyond the frost line.*
|This diagram represents the solar nebula early in its history, and shows the location of the frost line. Suppose you discover an object that is made of metal, rock, and ice. In which region of the solar system did it form?|
|-The shiny metal flakes embedded in rock are just what we expect if condensation really occurred as the nebular theory predicts.||This photo shows a slice of a meteorite. What is its significance?|
-The surprisingly flat face of the meteorite indicates that the solar nebula must have been very hot in the region in which this meteorite formed.
|-the formation of a jovian planet|
*The jovian planet forms in the center of the region shown in the box, and moons form in the disk around the forming planet.*
|What is being shown in the zoom-out box of this painting?|
-the solar nebula
|-It blasted away debris that then accreted in Earth orbit to form the Moon.|
*In other words, this painting shows the giant impact thought to be responsible for the formation of our Moon.*
|This painting shows an object colliding with Earth. What is thought to have happened as a result of this collision?|
-The impact released the heat that allowed Earth to undergo differentiation.
|-Potassium-40 has a half-life of 1.25 billion years.|
*Notice that the red curve for potassium-40 showing that half of it would decay after 1.25 billion years, which is why that point is labeled 1 half-life.*
|What can you conclude from studying this graph?|
-Potassium-40 has a half-life of 1.25 billion years.
|-2 billion years|
*We can see this fact by recognizing that the current fraction of potassium-40 is 1/3, or 0.33. Looking at the red curve for potassium-40, we see that it reaches about 0.33 on the vertical axis when the time is about 2 billion years.*
|You find a rock containing radioactive potassium-40 and its decay product argon-40. You assume that all the argon-40 was made from radioactive decay of potassium-40. The rock now has twice as much argon-40 as potassium-40; that is, 2/3 of the original potassium-40 has decayed into argon-40 while 1/3 remains in the rock. Based on this graph, about how old is the rock?|
-3 billion years
-1.25 billion years
-1 billion years
-2.5 billion years
-2 billion years
|Which of the following best explains why we can rule out the idea that planets are usually formed by near-collisions between stars?|
-A near collision might have created planets, but it could not have created moons, asteroids, or comets.
|-Stellar near-collisions are far too rare to explain all the planets now known to orbit nearby stars.|
*The near-collisions (close encounter) idea seemed unlikely even before we knew of extrasolar planets, but the existence of many other planetary systems makes it completely implausible.*
|According to our modern science, which of the following best explains why the vast majority of the mass of our solar system consists of hydrogen and helium gas?|
-All the other elements escaped from the solar nebula before the Sun and planets formed.
|-Hydrogen and helium are the most common elements throughout the universe, because they were the only elements present when the universe was young.|
*In other words, the chemical composition of the solar system is fairly close to that of the universe as a whole.*
|According to our theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size?|
-The two laws of thermal radiation
|-The law of conservation of energy|
*As it shrank in size, gas particles lost gravitational potential energy. Since energy must be conserved, this energy became thermal energy.*
|According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size?|
-The law of conservation of angular momentum
|-The law of conservation of angular momentum|
*To conserve angular momentum, the cloud particles had to move faster around the cloud center as their distance from the center decreased*
|According to our present theory of solar system formation, which of the following best explains why the solar nebula ended up with a disk shape as it collapsed?|
-The force of gravity pulled the material downward into a flat disk.
|-It flattened as a natural consequence of collisions between particles in the nebula.|
|What is the primary basis upon which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; metal)?|
-The amounts of energy required to ionize various materials.
|-The temperatures at which various materials will condense from gaseous form to solid form.|
|According to our present theory of solar system formation, which of the following statements about the growth of terrestrial and jovian planets is not true?|
-The terrestrial planets formed inside the frost line of the solar nebula and the jovian planets formed beyond it.
|-The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal.|
*The planetesimals in the outer solar system were not made only of ice: they also contained rock and metal. Remember, if it’s cold enough for ices to condense from hydrogen compounds, it’s certainly cold enough for rock and metal to condense as well.*
|Many meteorites appear to have formed very early in the solar system’s history. How do these meteorites support our theory about how the terrestrial planets formed?|
-Their appearance and composition matches what we observe in comets today, suggesting that they were once pieces of icy planetesimals.
|-The meteorites appearance and composition is just what we’d expect if metal and rock condensed and accreted as our theory suggests.|
|According to present understanding, which of the following statements about the solar wind is not true?|
-It swept vast amounts of gas from the solar nebula into interstellar space.
|-It is even stronger today than it was when the Sun was young.|
|According to our present theory of solar system formation, how did Earth end up with enough water to make oceans?|
-The water was mixed in the other materials in the planetesimals that accreted at our distance from the Sun.
|-The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars.|
*Water ice could condense from the solar nebula gas only beyond the frost line, which lay beyond the orbit of Mars.*
|What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits?|
-Some moons are surprisingly large in size.
|-Some moons have orbits that are “backwards” (compared to their planet’s rotation) or highly inclined to their planet’s equator.|
|Which of the following is not a line of evidence supporting the hypothesis that our Moon formed as a result of a giant impact?|
-Computer simulations show that the Moon could really have formed in this way.
|-The Pacific Ocean appears to be a large crater – probably the one made by the giant impact.|
*The Pacific Ocean is not an impact crater. Moreover, since the continents are rearranged with time, we can be sure that the giant impact occurred long, long before there was a Pacific Ocean*
|Why are terrestrial planets denser than jovian planets?|
-Actually, the jovian planets are denser than the terrestrial planets.
|-Only dense materials could condense in the inner solar nebula.|
*It was hotter in the inner regions, so only metal and rock could condense – and these materials are denser than the icy material that condensed farther out in the solar system.*
|Suppose you find a rock that contains 10 micrograms of radioactive potassium-40, which has a half-life of 1.25 billion years. By measuring the amount of its decay product (argon-40) present in the rock, you conclude that there must have been 80 micrograms of potassium-40 when the rock solidified. How old is the rock?|
-3.75 billion years
|-3.75 billion years|
*The current 10 micrograms of potassium-40 is 1/8 of the original 80 grams, which means the amount of potassium-40 has declined by a factor of 8. Therefore, three half-lives have passed (since 23 = 8) and the rock is 3(1.25 = 3.75 billion years old.*
|How do scientists determine the age of the solar system?|
-Theoretical calculations tell us how long it has taken the planets to evolve to their present forms
|-Radiometric dating of meteorites|
*The oldest meteorites are presumed to be material that condensed early in the history of the solar system and therefore represent the time at which the planets began to form.*
|The region of our solar system between Mercury and Mars has very few asteroids, while the region between Mars and Jupiter has many asteroids. Based on what you have learned, what is the most likely explanation for the lack of asteroids between Mercury and Mars?|
-Gravity was too weak to allow asteroids to form in this part of the solar system.
|-There were very few planetary leftovers in this region, because most of the solid material was accreted by the terrestrial planets as the planets formed.|
|About 2% of our solar nebula consisted of elements besides hydrogen and helium. However, the very first generation of star systems in the universe probably consisted only of hydrogen and helium. Which of the following statements is most likely to have been true about these first-generation star systems?|
-Jovian planets in these first-generation star systems had clouds made of water and other hydrogen compounds.
|-There were no comets or asteroids in these first-generation star systems.|
*Asteroids are made from metal and rock, and comets are made mostly of frozen hydrogen compounds – and all these materials require elements besides hydrogen and helium.*
|What is an extrasolar planet?|
-a planet that orbits a star that is not our own Sun
|-a planet that orbits a star that is not our own Sun|
|The first confirmed detections of extrasolar planets occurred in ____________.|
|Based on available data, what kind of objects in our solar system do most of the known extrasolar planets resemble?|
|Which new idea has been added into our theory of solar system formation as a result of the discoveries of extrasolar planets?|
-In addition to the categories of terrestrial and jovian, there must be an “in-between” category of planet that has the mass of a jovian planet but the composition of a terrestrial planet.
|-Jovian planets can migrate from the orbits in which they are born.|
|Which detection techniques can find the planet’s orbital distance (assuming we know the mass of the star)?|
-only the astrometric technique
|-all of these techniques|
|Why do we say that the Doppler technique gives the planet’s “minimum mass”?|
-The size of the Doppler shift that we detect depends on knowing the star’s mass, which can be very uncertain.
|-The size of the Doppler shift that we detect depends on whether the planet’s orbit is tilted.|
|How do we use velocity curves (obtained from spectroscopy) to show that some extrasolar planets are close to their host stars?|
-The velocity curve of the extrasolar planet shows periods much shorter than a year.
|-The velocity curve of the host star shows periods much shorter than a year.|
|Which of the following orbital characteristics has NOT been observed among any known extrasolar planets?|
Check all that apply.
-orbital speeds that are so slow that we cannot explain them
|-orbital speeds that are so slow that we cannot explain them|
-orbits that are not elliptical
|What method has detected the most extrasolar planets so far?|
-the transit method
|-the Doppler technique|
|Which one of the following can the transit method tell us about a planet?|
|Which method could detect a planet in an orbit that is face-on to the Earth?|
|Most extrasolar planets discovered so far most resemble|
|Most known extrasolar planets are more massive than Jupiter because|
-we do not expect smaller planets to exist.
|-current detection methods are more sensitive to larger planets.|
|Which of the following properties can be inferred from the star’s orbital period?|
-the planet’s orbital radius
|-the planet’s orbital radius|
*You can confirm this fact by moving the orbital radius slider. The orbital period of the star is the number of days between the peaks on the curve in the lower window, and changing the orbital radius of the planet changes the orbital period. This is a consequence of the fact that the star and planet must have the same orbital period, and Kepler’s third law tell us that the planet’s orbital period depends only on its orbital radius.*
|Is it possible to determine the planet’s mass from the star’s velocity curve?|
-yes, by measuring both the star’s orbital period and its change in velocity over the orbit
|-yes, by measuring both the star’s orbital period and its change in velocity over the orbit|
*You can confirm this fact with the animation as follows. First, move only the orbital radius slider without changing the planet mass; you will find that the star’s orbital period increases and its orbital velocity decreases. Now, move only the planet mass slider; you will see that this affects only the star’s orbital velocity. We conclude that you must know both the star’s orbital period and velocity to measure the planet’s mass. You can understand why if you recall that the star’s velocity depends on the strength of the gravitational tug from the planet, while the star’s orbital period depends only on the planet’s orbital radius (see Part A). Moving the planet farther from the star therefore increases the orbital period (in accord with Kepler’s third law) and weakens the gravitational tug. Increasing the planet’s mass increases the strength of gravity.*
|Consider the planet that causes the stellar motion shown in Plot 2 (be sure you have clicked the “Plot 2” button in the lower window of the animation). What can be said about a different planet orbiting the same star with an orbital period of 500 days?|
-The planet must be more massive.
|-The planet must be closer to the star.|
*Notice that 500 days is a shorter period than the period shown for Plot 2 (about 1200 days). According to Kepler’s third law, a shorter orbital period means that the planet must be closer to its star.*
|Based on what we know about our own solar system, the discovery of hot Jupiters came as a surprise to scientists because these planets are __________.|
|-so close to their stars|
*Hot Jupiters are jovian planets that are very close to their stars. Their discovery came as a surprise to scientists because in our solar system jovian planets are only found far from the Sun.*
|Our modern theory of solar system formation—the nebular theory—successfully accounts for all the major features of our own solar system. However, when the first hot Jupiters were discovered, their existence seemed inconsistent with the nebular theory because this theory predicts that __________.|
-any system with jovian planets should also have terrestrial planets
|-jovian planets can form only in the cold, outer regions of a solar system|
*The nebular theory holds that jovian planets form as the gravity of very large planetesimals draws in hydrogen and helium gas, and such large planetesimals can form only in the outer solar system where ices made of hydrogen compounds (such as water, methane, and ammonia) can condense along with metal and rock.*
|The discovery of hot Jupiters led scientists to reconsider the nebuar theory. Which of the following best explains why the nebular theory(as it stood before the discoveries of extrasolar planets) had not predicted the existence of hot Jupiters?|
-The nebular theory was designed to apply only to our solar system, so there was no reason to think it would apply to others.
|-There are no hot Jupiters in our solar system|
*In science, we seek models (theories) to explain observed phenomena; in this case, the lack of hot Jupiters in our own solar system meant there was nothing to explain when the nebular theory was developed. Once the hot Jupiters were discovered, it was natural that the nebular theory would need to be extended to accommodate them.*
|Today, the leading hypothesis for the existence of hot Jupiters is that they formed in their outer solar systems and then migrated inward. Why did this hypothesis gain favor over alternative ideas?|
-Computer models that simulate planetary formation show that interactions between young planets and other material in the surrounding disk can cause planetary migration.
|-Computer models that simulate planetary formation show that interactions between young planets and other material in the surrounding disk can cause planetary migration.|
*A scientific model uses equations and/or physical laws to make precise, testable predictions about observable phenomena. The agreement between computer models that predict migration and observations of hot Jupiters that have apparently migrated inward from their birthplaces is the reason that the migration hypothesis is now favored.*
|Assume that the migration hypothesis is the correct explanation for the hot Jupiters. In that case, the revised nebular theory looks just like the old theory, except that it now allows for the possibility of migration. Which of the following statements are consistent with this revised theory?|
Check all that apply.
-Terrestrial planets always form in the warm, inner regions of their star system.
|-Terrestrial planets always form in the warm, inner regions of their star system.|
-Jovian planets always form in the cold, outer regions of their star system.
-Jovian planets can migrate inward and disrupt the orbits of terrestrial planets.
*Migration can move orbits inward, but it cannot change their direction, which is why we still expect all planets to orbit in the same direction and nearly the same plane. We do not yet know how common systems like ours are, but we have no reason to think our solar system is particularly unusual.*
|How is the planet 51 Pegasi different from Jupiter?|
-much closer to its star
|-much closer to its star|
|Which detection method can be used on a backyard telescope with a CCD system?|
|Each item describes a characteristic that applies to one of the three planet-detection methods shown following. Match the items to the correct planet-finding method.||Doppler Method:|
-Used for most of the first 200 extrasolar planet detections
-Currently best suited to find Jupiter-sized extrasolar planets orbiting close to their stars
|The ___________________ was used to find a Jupiter-sized planet through careful measurements of the changing position of a star.||astrometric technique|
|Discovering planets through the ______________________ requires obtaining and studying many spectra of the same star.||Doppler technique|
|The _________________________ is currently searching for planet transits around some 100,000 stars.||Kepler mission|
|4. The ________________________ is used to find extrasolar planets by carefully monitoring changes in a star’s brightness with time.||transit technique|
|5. The ______________________________ is being designed to measure very small changes in stellar positions, which should allow it to discover many extrasolar planets.||GAIA Astrometry Mission|
|6. Proposed plans for the ___________________________________ would someday provide us with the first actual images and spectra of terrestrial worlds orbiting other stars.||Terrestrial Planet Finder mission|
|Why do scientists say that evolution is a “theory”?|
-because they are not very confident that it really happened
|-because it explains a great deal about life and is supported by an enormous body of evidence|
|In the Drake equation (Number of Civilizations ≡ N HP × f life × f civ × f now), what do we mean by f now?|
-the fraction of planets with civilizations at the present time (as opposed to only in the past or future)
|-the fraction of planets with civilizations at the present time (as opposed to only in the past or future)|
|Why don’t we expect to find life on planets orbiting high-mass stars?|
-The lifetime of a high-mass star is too short.
|-The lifetime of a high-mass star is too short.|
|We have sent several spacecraft on trajectories that will ultimately take them into interstellar space (Pioneer 10 and 11, Voyager 1 and 2, New Horizons). How long will it take these spacecraft to travel as far as the nearest stars?|
-a few decades
|-tens of thousands of years|
|-the precise wavelengths of spectral lines in the spectrum of the star|
*More precisely, the graph shows the Doppler shifts of these lines, which tell us the star’s speed toward or away from us at different times.*
|The graph above shows how a star’s orbital speed varies with time due to the gravitational tug of an orbiting planet. These data were obtained by measuring __________.|
-the precise brightness of the star divided by the precise brightness of the planet
*We can see this fact by noticing that the velocity graph has troughs at about 1.5 days and about 5.5 days, which means it took 4 days between them. This is the orbital period because the velocity data repeat each time the planet completes an orbit of the star.*
|The graph above shows how a star’s orbital speed varies with time due to the gravitational tug of an orbiting planet. Based on these data, the planet’s orbital period is about:|
|-the fact that large, icy objects orbit the Sun in the Kuiper belt|
*These data span only 65 years, which is not long enough to discover the existence of very low-mass objects (such as Pluto and Eris) that have orbital periods many times longer than 65 years.*
|This diagram shows the orbital path of the Sun around the center of mass of our solar system as it would appear from a distance of 30 light-years for the period 1960-2025. If aliens had constructed this graph at their home star system, they could learn all of the following except:|
-the fact that the Sun has more than two planets
*The large orbital velocity must be caused by a planet with greater mass than that shown in the other cases*
|The four graphs below show Doppler data for four different stars. Assume that all four stars have planetary systems oriented the same way toward Earth, so that the data can be compared fairly. Which graph reveals the existence of a planet with the greatest mass?|
*This graph shows the star having the longest orbital period of the 4 graphs, which means the planet also has the longest orbital period in this case.*
|The four graphs below show Doppler data for four different stars. Assume that all four stars have planetary systems oriented the same way toward Earth, so that the data can be compared fairly. Which graph reveals the existence of a planet with the longest orbital period?|
*The system is brightest at Point 1 because that is where you see the combined light from the star and the planet.*
|This diagram represents a star with an orbiting planet that, as seen from Earth, periodically transits across the face of the star and disappears behind the star. If you measure the brightness of this system, at which point would it be brightest?|
|-Many of these planets have orbits that differ significantly from perfect circles.|
*Notice that the eccentricities of many of the planets are much larger than those of the planets in our solar system, telling us that their orbits are not nearly circular.*
|Each dot on this graph represents an extrasolar planet; the green dots (labeled) represent planets of our own solar system. What can you conclude about the extrasolar planets shown on this graph?|
-The farther away a planet is from its star, the greater its eccentricity.
*Mass increases to the right on this graph, and point 4 is the farthest to the right.*
|This graph plots planetary mass on the horizontal axis and radius on the vertical axis. Notice the four locations marked by the bold numbers 1 through 4. Which location represents a planet with the greatest mass?|
*Notice the three density curves. Point 2 is the only point to the right of the highest density curve.*
|This graph plots planetary mass on the horizontal axis and radius on the vertical axis. Notice the four locations marked by the bold numbers 1 through 4. Which location represents a planet with the greatest density?|
*Notice that Point 3 is a terrestrial planet but is both higher up (larger in radius) and further right (larger in mass) than Earth.*
|This graph plots planetary mass on the horizontal axis and radius on the vertical axis. Notice the four locations marked by the bold numbers 1 through 4. Which location represents a planet has about the same composition as Earth but is larger in both size and mass?|
|From the viewpoint of an alien astronomer, how does Jupiter affect observations of our Sun?|
-It makes the Sun appear dimmer when viewed with infrared light.
|-It causes the Sun to move in a small ellipse with an orbital period of about 12 years.|
*Jupiter exerts a gravitational tug on the Sun, causing the Sun to move around their mutual center of mass with the same orbital period as Jupiter.*
|Why is it so difficult to take pictures of extrasolar planets?|
-Extrasolar planets give off light at different wavelengths than planets in our solar system.
|-Their light is overwhelmed by the light from their star.|
*A Sun-like star is about a billion times brighter than the light from a Jupiter-size planet orbiting it.*
|Suppose you are using the Doppler technique to look for planets around another star. What must you do?|
-Compare many spectra of the star taken over a period of many months or years.
|-Compare many spectra of the star taken over a period of many months or years.|
*We look for Doppler shifts in the star’s spectrum that, over time, shift back and forth to indicate the influence of an orbiting planet.*
|In general, which type of planet would you expect to cause the largest Doppler shift in the spectrum of its star?|
-a massive planet that is far from its star
|-a massive planet that is close to its star|
*Doppler shifts measure velocity, and the star will move faster if it experiences a greater gravitational tug from its planet. A massive, close-in planet will cause the strongest gravitational tug.*
|Suppose a planet is discovered by the Doppler technique and is then discovered to have transits. In that case, we can determine all the following about the planet except ______________.|
|-its rotation period|
*We do not get any direct information about rotation period. (However, if the planet is very close to its star, we can sometimes conclude that it has synchronous rotation, in which case the rotation period and orbital period are the same.)*
|The transit method allows us in principle to find planets around __________.|
-only stars of about the same mass and size as our Sun
|-only a small fraction of stars that have planets|
*We can see transits only if the planetary orbits are nearly precisely edge-on as viewed from Earth, which means that most planetary systems cannot be detected through transits. The Kepler mission overcomes this limitation by studying a large number of stars (about 150,000).*
|You observe a star very similar to our own Sun in size and mass. This star moves very slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet?|
-The planet must have a mass about the same as the mass of Jupiter.
|-The planet must be closer to the star than Earth is to the Sun|
*According to Kepler’s third law, a planet with a shorter orbital period must be closer to the star, assuming the star has the same mass as the Sun.*
|Which of the following will allow you to learn something about a transiting planet’s atmospheric composition?|
-Compare spectra obtained before and during an eclipse.
|-Compare spectra obtained before and during an eclipse.|
*The spectrum before the eclipse is that of the star and planet combined. The spectrum during eclipse, when the planet is behind its star, is that of the star alone. The difference between the two spectra therefore represents the planet’s spectrum, from which we learn about atmospheric composition.*
|Very few of the known extrasolar planets have sizes as small as Earth. The most likely reason for this fact is that ________.|
-small planets are usually made of materials that cannot be detected
|-small planets are more difficult to detect than larger planets|
|Based on everything you have learned about the formation of our solar system, which of the following statements is probably not true?|
-Planets are common, and many or most stars have them.
|-Only a tiny percentage of stars are surrounded by spinning disks of gas during their formation.|
*Spinning disks are a natural consequence of how we think stars form, which is one reason we expect planets to be quite common; the fact that we have now discovered hundreds of extrasolar planets lends further support to the idea that disks and planets should both be common.*
|To date, we’ve found very few planets orbiting their stars at distances comparable to the distances of the jovian planets in our solar system. Why do astronomers think this is the case?|
-We have not yet been searching for planets at such distances for a long enough time.
|-We have not yet been searching for planets at such distances for a long enough time.|
*Remember that we must observe at least something close to one complete orbit – and preferably more – before we can be confident of an extrasolar planet discovery. Jupiter takes 12 years to orbit the Sun, and Neptune takes 165 years – so we would need observations over similarly long period to detect planets in these types of orbits around other stars.*
|Current evidence suggests that some massive jovian planets orbit at very close orbital distances to their stars. How do we think these planets ended up on these close orbits?|
-These planets were able to form close to their stars because their solar nebulas were very cold in temperature.
|-These planets migrated inward after being born on orbits much farther from their stars.|
*We still think that jovian planets must form in cold, outer regions of their star systems, which is why the idea of migration was first proposed. Although work is still preliminary, models suggest that this type of migration is indeed likely.*
|Assuming that our ideas about how “hot Jupiters” ended up on their current orbits are correct, why didn’t our own solar system end up with any hot Jupiters?|
-The existence of Earth and the other terrestrial planets prevented the jovian planets from migrating inward.
|-Our solar nebula must have been blown into space shortly after the formation of the jovian planets.|
*This would prevent much inward migration from occurring.*
|When is the soonest we are likely to have moderate-resolution images and spectra of Earth-like planets around other stars?|
-In just a few years, through analysis of observations by the James Webb Space Telescope
|-In a decade or two, through space observatories now in the early planning stages|
*Scientists have numerous ideas about how they might obtain such images and spectra, but budgetary limitations mean that little work is being done in these areas right now.*
|Listed below are several geological and biological events in Earth’s history. Rank the events in the order in which they occurred, from first to last.||1. Giant Impact from Moon|
2. End of heavy bombardment
3. Early life (based on Fossil Evidence)
4. Oxygen build up in atmosphere
5. Animals colonize land
6. Earliest Mammals
7. Dinosaurs go extinct
8. Earliest Humans
|Earth was born about 4.5 billion years ago. According to current estimates, approximately how long after Earth’s formation did the Moon form?|
The Moon formed
-a few years later.
-a few tens of millions of years later.
-a few hundred million years later.
-more than a billion years later.
-at the same time as Earth.
|-a few tens of millions of years later|
*Evidence suggests that the giant impact that is thought to have formed the Moon occurred relatively shortly—within a few tens of millions of years—after Earth’s formation*
|The oldest fossil evidence of life dates to about __________ ago.|
-100 million years
|-3.5 to 4 billion years|
*The oldest intact fossils of microorganisms date to about 3.5 billion years ago, but carbon isotope evidence suggests that life may have been flourishing before about 3.85 billion years ago. If any life existed before 4 billion years ago, we are unlikely to be able to learn of it, because no rocks that old have yet been found.*
|Dinosaurs went extinct, probably because of an impact, about __________ ago.|
-5 million years
|-65 million years|
|Listed below are the names, spectral types (in parentheses), and approximate masses of several nearby main stars. Rank the stars based on the distances to their habitable zones (from the central star), from shortest to longest.||1. Bernard’s Star (M4) – 0.2 Msun|
2. 61 Cygni A (K5)- 0.7 Msun
3. Alpha Centauri A (G2) – 1Msun
4. Sirius (A1)- 2Msun
5. Spica (B1) 11Msun
*Notice that the ranking is in order of mass, because lower mass main-sequence stars are less luminous than higher mass stars. Therefore a planet would have to be located closer to a lower mass star than to a higher mass star in order to have a temperature warm enough for liquid water to exist.*
|Consider again the same set of five stars. This time, rank the stars based on the size (width) of their habitable zones, from smallest to largest.||1. Bernard’s Star (M4) – 0.2 Msun|
2. 61 Cygni A (K5)- 0.7 Msun
3. Alpha Centauri A (G2) – 1Msun
4. Sirius (A1)- 2Msun
5. Spica (B1) 11Msun
*Notice that the ranking is the same as that from Part A, because lower mass main-sequence stars not only have their habitable zones located closer to them but they also have the narrowest habitable zones. Higher mass stars have wider habitable zones because they have a greater range of distances in which a planet could potentially have liquid water on its surface.*
|Imagine that each of the five stars is orbited by a terrestrial planet at a distance of 1 AU (Earth’s distance from the Sun). Rank the stars based on the planet’s expected surface temperature (not including any greenhouse effect), from lowest to highest.||1. Bernard’s Star (M4) – 0.2 Msun|
2. 61 Cygni A (K5)- 0.7 Msun
3. Alpha Centauri A (G2) – 1Msun
4. Sirius (A1)- 2Msun
5. Spica (B1) 11Msun
*For a planet at any particular distance, such as 1 AU, a more luminous star means more energy (per unit area) reaching the planet’s surface—and more energy will tend to make the planet hotter. For example, if the Sun were more luminous, Earth would be hotter. That is why the rankings again go in order of increasing luminosity, which for main-sequence stars means increasing mass.*
|The items below describe worlds or selected localities on worlds. Based on our current scientific understanding, match these items to the appropriate category below.||Likely to be habitable:|
-Underground on Mars
– Subsurface ocean on Europa
-Moon with atmosphere orbiting Jovian planet 1AU from 1Msun star
Unlikely to be habitable:
|Which statement explains the observations that make it seem possible that Mars could have life underground?|
-We have detected subsurface wells of liquid water in equatorial regions of Mars.
|-We have detected water ice on Mars, and Mars still has some volcanic heat.|
*The combination of water ice and volcanic heat suggests that there could be liquid water underground.*
|In Part A you found that the terrestrial planet 10 AU from a 0.5MSun star is unlikely to be habitable. Could this planet be habitable if it were in a different orbit around its star?|
-Yes, if it had an eccentric orbit that sometimes brought it within 0.01 AU of its star.
|-Yes, but it would have to be less than 0.5 AU from its star.|
*Remember that a star half the mass of the Sun is much less than half as luminous as the Sun, so the star’s habitable zone would be located much less than 1 AU from the star.*
|As the mass of the central star increases, the distance to the habitable zone __________ and the size (width) of the habitable zone __________.|
Select from the choices in the format first blank / second blank.
-decreases / increases
|-increases / increases|
*The habitable zone is both farther from the star and larger in size for a higher-mass star than for a lower-mass star*
|Suppose that our Sun was cool enough to include Mercury in its habitable zone. Which of the following would be true in that case?|
-Only Mercury would be in the Sun’s habitable zone.
|-Only Mercury would be in the Sun’s habitable zone.|
*You can see this fact in the interactive figure by showing the solar system orbits and then moving the sliders until the habitable zone includes Mercury’s orbit. You’ll then notice that the habitable zone has become so small that none of the other planets of our solar system lie within it.*
|Scientists think it is very unlikely that complex and large forms of life could evolve on planets that orbit stars that are much more massive than the Sun. Why?|
-The expected lifetime of a massive star is too short to allow for the evolution of complex life
|-The expected lifetime of a massive star is too short to allow for the evolution of complex life|
*Recall that higher-mass stars have shorter lives. On Earth, fossil evidence indicates that life remained microscopic for hundreds of millions to billions of years after the origin of life, which itself was hundreds of millions of years after Earth’s birth some 4 1/2 billion years ago. Because any star with mass more than about 6 times that of the Sun has a lifetime less than 100 million years, it does not seem that such stars would live long enough for complex life to evolve, and perhaps not long enough for life of any kind to arise.*
|1. High-mass main-sequence stars have a more distant and wider __________________ than low-mass stars.||habitable zone|
|Sky surveys looking for radio signals generated by technology are part of the ________________________________________________________.||search for extraterrestrial intelligence|
|3. The is _____________________ designed as a way of estimating the number of intelligent civilizations in the Milky Way.||Drake equation|
|The notion that living organisms with advantages that give them greater reproductive success (in some local environment) will survive while others perish is an example of what Darwin called _________________________.||natural selection|
|5. One of the key premises for the ____________________________ is that living organisms are able to produce far more offspring than their environment can support.||theory of evolution|
|6. The different time periods of the __________________________ are defined by changes in fossils found from those time periods.||geological time scale|
|7. Incoming ultraviolet light from the Sun can cause a _____________ in a living organism’s DNA that can affect its ability to survive and reproduce||mutation|