Astronomy Homework 6

[QUESTION] Which of the following is a strong greenhouse gas? [1] nitrogen [2] water vapor [3] oxygen

[ANSWER] [2] water vapor

[QUESTION] Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once. [1.] The largest moon in the solar system is _______. [2.] The jovian moon with the most geologically active surface is _______. [3.] Strong evidence both from surface features and magnetic field data support the existence of a subsurface ocean on _______. [4.] _______ is responsible for the tremendous volcanic activity on Io. [5.] _______ is the most distant of Jupiter's four Galilean moons. [6.] The fact that Europa orbits Jupiter twice for every one orbit of Ganymede is an example of a(n) _______. [-] Callisto [-] Io [-] Ganymede [-] Tidal Heating [-] Orbital Resonance [-] Europa

[ANSWER] 1. The largest moon in the solar system is [Ganymede]. 2. The jovian moon with the most geologically active surface is [IO]. 3. Strong evidence both from surface features and magnetic field data support the existence of a subsurface ocean on [Europa]. 4. [Tidal Heating] is responsible for the tremendous volcanic activity on Io. 5. [Callisto] is the most distant of Jupiter's four Galilean moons. 6. The fact that Europa orbits Jupiter twice for every one orbit of Ganymede is an example of a(n) [Orbital Resonance].

[QUESTION] [1.] Most of the charged particles from the Sun are deflected around Earth by the_______. [2.] Earth's _______ absorbs most of the ultraviolet light arriving here from the Sun. [3.] Most of the X-rays coming from the Sun are absorbed in the _______. [4.] Gas particles in Earth's atmosphere most easily escape from the _______. [5.] The densest layer of the atmospheres of Venus, Earth, and Mars is the _______. [OPTIONS] - Magnetosphere - Thermosphere - Troposphere - Stratosphere - Exosphere

[ANSWER] [1.] Magnetosphere [2.] Stratosphere [3.] Thermosphere [4.] Exosphere [5.] Troposphere

[QUESTION] Listed following are characteristics of the atmospheres of Venus, Earth, and Mars. Match each atmospheric characteristic to the appropriate planet. [1.] Mars [2.] Earth [3.] Venus - Ultraviolet absorbing atmosphere - Almost no surface winds - Global Dust Storms - Runaway greenhouse effect - Extremely low-density atmosphere - Sulfuric acid clouds - Atmosphere composed primarily of nitrogen

[ANSWER] [1.] Mars - Global Dust Storms - Extremely low-density atmosphere [2.] Earth - Ultraviolet-absorbing stratosphere - Atmosphere composed primarily of nitrogen [3.] Venus - Runaway greenhouse effect - Almost no surface winds - Sulfuric acid clouds [EXPLANATION] Be sure to recognize that Venus has very little surface wind because of its slow rotation rate. Venus suffered a runaway greenhouse effect because of its distance from the Sun; If Earth were placed at the same distance, our planet would suffer the same fate. Earth has an ultraviolet-absorbing stratosphere because of the oxygen in the atmosphere, which at high altitudes forms molecules of ultraviolet-absorbing ozone.

[QUESTION] Listed following are some of the distinguishing geological characteristics of the moons orbiting Jupiter. Match each characteristic to the appropriate moon. [Io] [Europa] [Ganymede] [-] largest moon in the solar system [-] hot, glowing lava visible in some photos [-] source of ionized gas in the donut-shaped charged particle belt around jupiter [-] volcanoes currently erupting [-] surface features provide evidence of a subsurface liquid ocean [-] ice covered surface with few impact craters [-] heavily cratered terrain adjacent to much younger terrain

[ANSWER] [Io] [-] source of ionized gas in the donut-shaped charged particle belt around jupiter [-] hot, glowing lava visible in some photos [- volcanoes currently erupting [Europa] [-] surface features provide evidence of a subsurface liquid ocean [-] ice covered surface with few impact craters [Ganymede] [-] largest moon in the solar system [-] heavily cratered terrain adjacent to much younger terrain [Explanation] Remember that these differences are consequences of the different levels of tidal heating these moons experience. Io is very hot because it is the nearest of the three to Jupiter and has the most tidal heating; Europa is intermediate, and Ganymede has the least tidal heating of the three moons.

[QUESTION] Sort each of the planetary properties below based on whether they apply to some, all, or none of the four jovian planets in our solar system. [Jupiter and Saturn only] [Uranus and Neptune only] [all four jovian planets] [no jovian planets] [-] solid surface under a thick atmosphere [-] interior is mostly liquid or metallic hydrogen [-] composed mostly of hydrogen and helium [-] magnetic field stronger than Earth's [-] composed mostly hydrogen compounds [-] blue color because of methane [-] orbited by rings of ice and rock [-] strong atmospheric winds and storms [-] approximately 10 Earth-mass core

[ANSWER] [Jupiter and Saturn only] [-] interior is mostly liquid or metallic hydrogen [-] composed mostly of hydrogen and helium [Uranus and Neptune only] [-] blue color because of methane [-] composed mostly hydrogen compounds [all four jovian planets] [-] approximately 10 Earth-mass core [-] orbited by rings of ice and rock [-] magnetic field stronger than Earth's [-] strong atmospheric winds and storms [no jovian planets] [-] solid surface under a thick atmosphere [EXPLANATION] The jovian planets share many characteristics in common such as approximate core size, severe weather, rings and numerous moons, and strong magnetic fields. Jupiter and Saturn have similar compositions of hydrogen and helium, while Uranus and Neptune are composed primarily of hydrogen compounds. Unlike the terrestrial planets, the jovian planets do not have solid surfaces.

[QUESTION] [PART A] The following images show four types (wavelengths) of light. Rank these from left to right based on the amount of each that is emitted (as thermal radiation) by Earth's surface, from greatest to least. If you think that two (or more) types should be ranked as equal, drag one on top of the other(s) to show this equality. [-] Infrared [-] Visible [-] X-Ray [-] Ultraviolet (UV) ________________________________________________________________ [PART B] In Part A, you found that Earth emits only infrared light. This infrared light can be absorbed by greenhouse gases, such as carbon dioxide and water vapor, in the atmosphere. In fact, all the terrestrial planets emit infrared light from their surfaces. The following images show the four terrestrial planets in our solar system. Rank these planets from left to right based on the total amount of infrared-absorbing greenhouse gases in their atmospheres, from greatest to least. [-] Venus [-] Mars [-] Earth [-] Mercury ________________________________________________________________ [PART C] The following images show the four terrestrial planets in our solar system. Rank the planets from left to right based on the strength of the greenhouse effect occurring at their surfaces, from strongest to weakest. [-] Venus [-] Mars [-] Earth [-] Mercury ________________________________________________________________ [PART D] The following images show the four terrestrial planets in our solar system. Rank the planets from left to right based on the amount by which the greenhouse effect increases their surface temperatures, compared to what their temperatures would be without the greenhouse effect, from largest to smallest increase. [-] Venus [-] Mars [-] Earth [-] Mercury

[ANSWER] [PART A] - Greatest Amount [-] Infrared - Least Amount [-] Visible [-] X-Ray [-] Ultraviolet (UV) [Explanation] Earth emits thermal radiation characteristic of its surface temperature, which means it is almost entirely infrared (extending, in principle, down into the radio). For Earth, the surface temperature is too low to emit any visible, ultraviolet, or X-ray light, so those are all ranked equally. (Note: Technically, thermal emission extends over all wavelengths, so even at low temperatures there might be an occasional photon of visible or higher-energy radiation. However, this emission is negligible for Earth, which is why we rank them all equal to zero.) ________________________________________________________________ [PART B] - Greatest Greenhouse Gas Abundance [-] Venus [-] Earth [-] Mars [-] Mercury - Least Greenhouse Gas Abundance [Explanation] Venus has a thick atmosphere of carbon dioxide. Earth has greenhouse gases primarily in the form of water vapor, carbon dioxide, and methane. Mars has an atmosphere made mostly of carbon dioxide, but its atmosphere is so thin that it contains less total greenhouse gas than Earth's atmosphere. Mercury has essentially no atmosphere at all. ________________________________________________________________ [PART C] - Strongest [-] Venus [-] Earth [-] Mars [-] Mercury - Weakest [Explanation] The greenhouse effect is caused by greenhouse gases in the atmosphere, so more greenhouse gas means a stronger greenhouse effect. That is why the rankings here are the same as the rankings for Part B. ________________________________________________________________ [PART D] - Largest Increase [-] Venus [-] Earth [-] Mars [-] Mercury - Smallest Increase [Explanation] A stronger greenhouse effect means a greater temperature increase, which is why the rankings here are the same as the rankings for Parts B and C. The differences are quite extreme: Mercury has no greenhouse effect, so its temperature is determined solely by its distance from the Sun and its reflectivity. The greenhouse effect raises the temperature of Mars by about 6°C from what it would be otherwise; it raises Earth's temperature by about 31°C (which means our planet would be frozen over without the greenhouse effect); and it raises Venus's temperature by about 510°C, explaining the extremely high temperature of Venus.

[QUESTION] [PART A] Which of the following statements best describes the general pattern of composition among the four jovian planets? [1] Uranus and Neptune contain relatively more rock and hydrogen compounds than Jupiter and Saturn. [2] Jupiter is made mostly of hydrogen and helium, while the other three jovian planets are made mostly of hydrogen compounds. [3] Jupiter is made mostly of hydrogen, Saturn is made mostly of helium, Uranus is made mostly of hydrogen compounds, and Neptune is made mostly of rock. [4] All four planets have essentially the same composition. ________________________________________________________________ [PART B] Look at the average densities of the jovian planets given in Figure 1. Can you identify a trend in jovian planet densities with mass or distance from the Sun? [1] There is no clear trend in the densities with mass or distance. [2] The densities increase in order of distance from the Sun. [3] The more massive the planet, the lower the density. [4] The more massive the planet, the higher the density. [5] The densities decrease in order of distance from the Sun. ________________________________________________________________ [PART C] Which of the following statements best explains why the densities of Uranus and Neptune are higher than that of Saturn, even though Saturn is much more massive? [1] They have a higher proportion of hydrogen compounds and rock. [2] Their interiors are more compressed due to stronger gravity. [3] They have stronger magnetic fields. [4] They are at greater distances from the Sun. [5] They have higher masses. ________________________________________________________________ [PART D] Which of the following best explains why Jupiter's density is higher than Saturn's? [1] Jupiter is more massive than Saturn. [2] Jupiter has a stronger magnetic field than Saturn. [3] Jupiter has a higher proportion of hydrogen compounds and rock than Saturn. [4] Jupiter is closer to the Sun than Saturn. ________________________________________________________________ [PART E] Based on the leading scientific theory of solar system formation, which of the following statements best explains why Uranus and Neptune have a significantly different composition than Jupiter and Saturn? [1] Jupiter and Saturn formed closer to the Sun, where there was more hydrogen and helium gas and less hydrogen compounds and rock. [2] Jupiter and Saturn captured more gas from the solar nebula than Uranus and Neptune. [3] The lower temperatures at the locations of Uranus and Neptune allowed more material to condense into solid form into solid form. [4] The lower masses of Uranus and Neptune allowed more of their hydrogen and helium gas to escape into space.

[ANSWER] [PART A] [1] Uranus and Neptune contain relatively more rock and hydrogen compounds than Jupiter and Saturn. [EXPLANATION] As the figure shows, Jupiter and Saturn are made mostly of hydrogen and helium, while Uranus and Neptune are primarily made of hydrogen compounds — such as water (H2O), methane (CH4), and ammonia (NH3) — along with a substantial relative amount of rock. ______________________________________________________________ [PART B] [1] There is no clear trend in the densities with mass or distance. [EXPLANATION] There is no obvious trend in the average densities of the jovian planets. For example, Jupiter is the nearest and most massive of the four planets, but it is the second-highest in average density. The lack of a clear trend tells us that we need to look deeper at the nature of these planets in order to understand their densities. ______________________________________________________________ [PART C] [1] They have a higher proportion of hydrogen compounds and rock. [EXPLANATION] At similar temperature and pressure, hydrogen compounds and rock are much higher in density than hydrogen and helium. The internal conditions in the jovian planets are similar enough so that composition has a major effect on average density. Uranus and Neptune are higher in density than because they are made primarily of higher-density hydrogen compounds and rock. ______________________________________________________________ [PART D] [1] Jupiter is more massive than Saturn. [EXPLANATION] Because Jupiter and Saturn have nearly identical composition, Jupiter's higher density indicates that its interior is more compressed than Saturn's. This greater compression is due to gravity, which is stronger for Jupiter because of its greater mass. ______________________________________________________________ [PART E] [2] Jupiter and Saturn captured more gas from the solar nebula than Uranus and Neptune. [EXPLANATION] Accretion is thought to have occurred more rapidly in the denser regions of the solar nebula that were closer to the Sun. Therefore, although all four jovian planets captured hydrogen and helium gas from the solar nebula around similar-mass planetesimals (made of hydrogen compounds and rock), Jupiter and Saturn had more time to capture this gas. As a result, Jupiter and Saturn accreted so much hydrogen and helium gas that these ingredients ended up dominating their composition. In contrast, Uranus and Neptune were left with compositions dominated by hydrogen compounds and rock.

[QUESTION] [Part A] The average temperature over the past 1000 years has been about 15∘C. From the graphs, you can conclude that Earth's average temperature during the past 800,000 years has __________. [1] never been as high as it is today [2] stayed remarkable steady, never varying by more than about 2∘C [3] varied between about 7∘C and 19∘C [4] varied between about −10∘C and +4∘C ________________________________________________________________ [Part B] On the graphs shown, you can identify an ice age by looking for __________. [1] a trough (bottom of a dip) on the carbon dioxide graph [2] a place on the temperature graph where the temperature curve falls steeply [3] a peak on the temperature graph [4] a trough (bottom of a dip) on the temperature graph ________________________________________________________________ [Part C] Notice that the peaks and troughs on the temperature graph occur at the about the same times as peaks and troughs on the carbon dioxide graph. What can we infer from this fact alone? [1] The carbon dioxide concentration is inversely related to the global average temperature. [2] There is a correlation between the carbon dioxide concentration and the global average temperature. [3] Higher carbon dioxide concentrations cause higher global average temperatures. [4] Higher global average temperatures cause higher carbon dioxide concentrations. ________________________________________________________________ [Part D] Although the data show only a correlation between the carbon dioxide concentration and the global average temperature, scientists have other reasons to think that a rise in the carbon dioxide concentration actually causes a rise in the global average temperature. All of the following statements are true. Which statements lend support to the idea that carbon dioxide is a cause of planetary warming? [-] We understand the physical mechanism of the greenhouse effect, through which carbon dioxide can increase a planet's temperature. [-] Models of the greenhouse effect successfully predict the temperatures of Venus and Mars from their atmospheric carbon dioxide amounts. [-] Models of Earth's climate that include recent increases in the carbon dioxide concentration match observed temperature increases better than those that do not include it. [-] Isotope ratios in atmospheric carbon dioxide show that much of the carbon dioxide in Earth's atmosphere today comes from the burning of fossil fuels. ________________________________________________________________ [Part E] Based on the evidence that atmospheric carbon dioxide is a cause of planetary warming, what aspect of the graphs should most concern us? [1] The carbon dioxide concentration today is significantly higher than at any time in the past 800,000 years and is rapidly rising. [2] Earth's past temperature rises and falls naturally. [3] Earth's past carbon dioxide concentration rises and falls naturally. ________________________________________________________________ [Part F] Make a prediction: If the rise in carbon dioxide concentration continues at its current pace, the concentration in the year 2050 will be about _____ parts per million. [1] 400 [2] 430 [3] 460 [4] 510

[ANSWER] [Part A] [3] varied between about 7∘C and 19∘C [Explanation] The zero level on the graph represents the 15∘C average temperature over the past millennium, so the peaks near +4 on the graph represent a temperature of about 15∘C+4∘C=19∘C and the troughs near −8 represent 15∘C−8∘C=7∘C. ________________________________________________________________ [Part B] [4] a trough (bottom of a dip) on the temperature graph [Explanation] For example, the graph shows that the most recent ice age ended only about 10,000 years ago, and there are numerous other ice ages shown on the graph. ________________________________________________________________ [Part C] [2] There is a correlation between the carbon dioxide concentration and the global average temperature. [Explanation] A correlation means that two things go up and down together. In this case, there is a correlation between the temperature and the carbon dioxide concentration because both were generally high at the same times in the past and low at the same times in the past. ________________________________________________________________ [Part D] [-] We understand the physical mechanism of the greenhouse effect, through which carbon dioxide can increase a planet's temperature. [-] Models of the greenhouse effect successfully predict the temperatures of Venus and Mars from their atmospheric carbon dioxide amounts. [-] Models of Earth's climate that include recent increases in the carbon dioxide concentration match observed temperature increases better than those that do not include it. [Explanation] Together, the success of the models and our clear understanding of the mechanism of the greenhouse effect leave little room for doubt that carbon dioxide is indeed a cause of higher temperatures on a planet. ________________________________________________________________ [Part E] [1] The carbon dioxide concentration today is significantly higher than at any time in the past 800,000 years and is rapidly rising. [Explanation] Therefore, if past trends continue, we would expect Earth's temperature to rise substantially as a result of this increase in the carbon dioxide concentration. ________________________________________________________________ [Part F] [3] 460 [Explanation] Note that this concentration would be more than 60% higher than the concentration of 280 parts per million at the beginning of the industrial age (around the year 1750). It is also far higher than the carbon dioxide concentration reached naturally during the prior 800,000 years. In fact, the situation could be even worse: Careful study of the graph shows an acceleration of the rate of increase in recent years, which would lead the carbon dioxide concentration to be even higher than 460 parts per million by 2050.

[QUESTION] [Part A] The energy that warms Earth's surface comes primarily in the form of __________. [1] infrared light from the Sun [2] heat from the Sun [3] visible light from the Sun [4] heat from Earth's interior [5] ultraviolet light from the Sun ________________________________________________________________ [Part B] Earth's temperature remains fairly steady, which means that Earth must return nearly the same amount of energy to space that it receives from the Sun. In what form(s) does Earth return most of this energy to space? [-] ultraviolet light reflected by the surface [-] visible light reflected by the surface [-] visible light reflected by clouds [-] infrared light emitted by the surface and atmosphere [-] visible light emitted by the surface and atmosphere ________________________________________________________________ [Part C] Greenhouse gases in the atmosphere, such as carbon dioxide and water vapor, make Earth warmer than it would be otherwise because these gases __________. [1] form clouds that emit thermal radiation [2] absorb visible light coming from the Sun [3] reflect visible light coming from the Sun [4] absorb infrared light emitted by the surface ________________________________________________________________ [Part D] According to scientists, the naturally occurring greenhouse effect makes Earth about 31∘C warmer than it would be if there were no greenhouse gases in our atmosphere. How do scientists "know" what Earth's temperature would be without greenhouse gases? [1] Ancient fossils allow them to infer Earth's temperature at a time before our atmosphere contained greenhouse gases. [2] They calculate this temperature from Earth's reflectivity and distance from the Sun. [3] They assume that this temperature would be about the same as the temperature of Mars, which has much less of an atmosphere than Earth. [4] They estimate it by averaging guesses made by many individual scientists. ________________________________________________________________ [Part E] All of the following statements are true. Which one provides strong observational support for the claim that greenhouse gases make a planet warmer than it would be otherwise? [1] Earth is the only planet with an ozone layer in its atmosphere. [2] Earth has a higher average temperature than Mars. [3] Venus has a higher average temperature than Mercury. [4] Mercury is much hotter than the Moon. ________________________________________________________________ [Part F] Based solely on an understanding of the greenhouse effect (as displayed in the figure), which one of the following statements is true? [1] We do not yet understand the greenhouse effect well enough to make predictions about how it affects our planet. [2] We should expect an increase in the greenhouse gas concentration to lead to global warming. [3] Global warming poses a grave threat to our future. [4] Humans are causing global warming.

[ANSWER] [Part A] [3] visible light from the Sun [Explanation] In the figure, this fact is illustrated by the yellow squiggly line at the far left. ________________________________________________________________ [Part B] [-] visible light reflected by the surface [-] visible light reflected by clouds [-] infrared light emitted by the surface and atmosphere [Explanation] The total amount of energy returned to space in these three forms of radiation is nearly equal to the amount of energy that reaches Earth in the form of sunlight, which is why Earth's average temperature stays fairly steady. (Note: global warming is occurring, but the change is taking place over time scales of years, which means the incoming and outgoing energy at any moment are quite closely balanced.) ________________________________________________________________ [Part C] [4] absorb infrared light emitted by the surface [Explanation] Although the absorbed infrared light is quickly reemitted, it is reemitted in a random direction. As a result, greenhouse gases tend to slow the escape of infrared light from Earth to space, so that there is more heat (which means more energy) in the atmosphere than there would be if the infrared light escaped directly to space. ________________________________________________________________ [Part D] [2] They calculate this temperature from Earth's reflectivity and distance from the Sun. [Explanation] Aside from the greenhouse effect, the only factors that affect a planet's average temperature are its reflectivity and distance from the Sun. Since both distance and reflectivity have been measured, the expected temperature can be calculated easily and precisely. (Note that this assumes that the Sun's total emission of energy remains steady; measurements and theory both indicate that it varies very little over time scales less than a few million years.) ________________________________________________________________ [Part E] [3] Venus has a higher average temperature than Mercury. [Explanation] The fact that Venus is hotter than Mercury despite being nearly twice as far from the Sun tells us that its thick carbon dioxide atmosphere must warm it significantly—just as we expect from the theory of the greenhouse effect. ________________________________________________________________ [Part F] We should expect an increase in the greenhouse gas concentration to lead to global warming. [Explanation] The evidence discussed in this tutorial makes it clear that greenhouse gases make a planet's surface warmer than it would otherwise be, so we should expect a rise in the greenhouse gas concentration to make Earth warmer. It is possible that there can be mitigating factors through feedbacks, but the basic link between greenhouse gas concentration and global warming is very strong.

[QUESTION] Which terrestrial world has the most atmosphere? [1] Venus [2] Earth [3] Mars

[ANSWER] [1] Venus

[QUESTION] In which direction do hurricanes in the Southern Hemisphere rotate? [1] clockwise [2] counterclockwise [3] either direction

[ANSWER] [1] clockwise

[QUESTION] Why is the sky blue (on Earth)? [1] No one knows—this is one of the great mysteries of science. [2] because molecules scatter blue light more effectively than red light [3] because the Sun emits mostly blue light [4] because molecules scatter red light more effectively than blue light. [5] because deep space is blue in color

[ANSWER] [2] because molecules scatter blue light more effectively than red light

[QUESTION] What kind of gas is most affected by thermal escape? [1] greenhouse gases [2] light gases [3] all gases equally

[ANSWER] [2] light gases

[QUESTION] Which of the following is a general characteristic of the four jovian planets in our solar system? [1] They have very little hydrogen, helium, and hydrogen compounds. [2] They are less massive then any of the terrestrial planets. [3] They are lower in average density than are the terrestrial planets. [4] They have solid surfaces.

[ANSWER] [3] They are lower in average density than are the terrestrial planets.

[QUESTION] Which of the following correctly lists the terrestrial worlds in order from the thickest atmosphere to the thinnest atmosphere? (Note: Mercury and the Moon are considered together in this question.) [1] Venus, Mars, Moon/Mercury, Earth [2] Mars, Venus, Earth, Moon/Mercury [3] Venus, Earth, Mars, Moon/Mercury [4] Earth, Venus, Mars, Moon/Mercury

[ANSWER] [3] Venus, Earth, Mars, Moon/Mercury

[QUESTION] Where is most of the CO2 that has outgassed from Earth's volcanoes? [1] in the atmosphere [2] escaped into space [3] locked up in rocks

[ANSWER] [3] locked up in rocks

[QUESTION] Some jovian planets give off more energy than they receive because of [1] fusion in their cores. [2] tidal heating. [3] ongoing contraction or differentiation.

[ANSWER] [3] ongoing contraction or differentiation.

[QUESTION] What causes the release of oxygen into Earth's atmosphere? [1] outgassing [2] evaporation/sublimation [3] photosynthesis

[ANSWER] [3] photosynthesis

[QUESTION] Suppose that Earth's atmosphere had no greenhouse gases. Then Earth's average surface temperature would be _______. [1] slightly cooler, but still above freezing [2] about the same as it is now [3] well below the freezing point of water [4] slightly warmer, but still well below the boiling point of water

[ANSWER] [3] well below the freezing point of water

[QUESTION] Which of the following is NOT an expected consequence of global warming? [1] melting of polar ice and glaciers [2] an increase in the number and intensity of hurricanes [3] an increase in the severity of winter blizzards [4] warming up of the entire Earth by the same amount

[ANSWER] [4] warming up of the entire Earth by the same amount