Physics 20073 - Fall 2000 Complete Study Guide

(1): Given the angular size equation, explain how we can find the distance to the Moon simply by knowing its apparent angular size and its diameter? Use a simple diagram to explain how the angular size is related to the distance and the diameter (i.e. If the Moon had a larger angular size and the same diameter, would that imply it is closer or further away?).
(2): Given the parallax equation, explain how we use parallax angles to find the distance to other planets. Be able to show (with a simple diagram) why the parallax angle is inversely proportional to the distance to the object and why it is directly proportional to the baseline length.
(3): Two basic reasons why the heliocentric theory of the solar system was not accepted by scientists in Copernicus' time were the lack of a strong wind and the lack of measured stellar parallax angles. Explain these two pieces of evidence and why they seemed to argue against the heliocentric model.
(4): Galileo's observations of the phases of Venus and the moons in orbit around Jupiter were both seen as evidence in opposition to the geocentric model. Explain why.
(5): Based on the reading Cargo Cult Science, imagine your task is to explain to a South Sea islander why planes don't land there anymore even though the islanders are going through the proper motions that have made planes land there in the past. Come up with your own honest explanation of why this is true in three or four sentences (which, not coincidentally, is about the length of an average exam answer). (TQ #1)
(6): Explain why we see different constellations overhead at midnight at different times of the year.
(7): Explain the concept of a sidereal day with the help of a simple diagram. Explain how a sidereal day is different from a solar day.
(8): As seen from above the north pole, the Earth rotates counterclockwise on its axis, and it orbits counterclockwise around the Sun. Suppose the Earth's spin were the same but it were orbiting the Sun in a clockwise direction. How would the length of the sidereal day compare to the length of the solar day? What if both the spin and the orbital direction were clockwise? Justify your answers with some simple diagrams. (TQ #2)
(9): For different latitudes on the Earth, explain where the North Celestial Pole can be found on the sky. In other words, use a simple diagram to help explain why the altitude of the NCP above the northern horizon is equal to an observer's northern latitude on the Earth.
(10): Be able to draw a simple horizon diagram (horizon plus hemispherical sky) from any latitude on Earth showing the altitude above the horizon of the NCP, Celestial Equator and SCP (if applicable).
(11): What is the ecliptic? What is the difference between the Sun's daily path and its annual path? Be able to draw this difference on a simple celestial sphere diagram.
(12): A common misconception is that the seasons are caused by the Earth being closer to or further away from the Sun. Name and explain a simple piece of evidence that contradicts this idea.
(13): Although the northern hemisphere of the Earth is slightly closer to the Sun than the southern hemisphere (during the northern hemisphere's summer), this shouldn't result in a significant difference in temperature between the two hemispheres. Explain why.
(14): Be able to use a horizon diagram to help explain the mechanism behind the Earth's seasonal variations.
(15): On a horizon diagram, be able to draw the June, Mar/Sep and December paths of the Sun from the various latitudes on the Earth.
(16): If the Earth's axis were not tilted (thus, it would make an angle of 90 degrees with respect to the plane of the Ecliptic), would we have seasons? What would the paths of the Sun look like at different times of the year from the North Pole? From Fort Worth? Explain. (TQ #3)
(17): Explain why circumpolar stars are found at high celestial latitudes (high declinations). A diagram may help.
(18): Be able to use a diagram like that found in Box 2-3 on page 38 of the text to explain why during northern summers the Sun's altitude is higher in the sky and the days are longer, thus resulting in warmer temperatures.
(19): One theory that attempts to explain the Moon's phases is that they are caused by the shadow of the Earth falling on the Moon. Diagram the relative positions of the Earth, Moon and Sun during a crescent moon phase to disprove this idea.
(20): Explain how we know, using mathematical arguments (and the equation of angular size) that the full moon has the same angular size whether it is nearly overhead or near the horizon. What simple experiment could you perform to prove this? Explain.
(21): Be able to explain what causes the lunar phases. Given a diagram of the Sun, Earth and Moon, be able to indicate which phase the Moon is in (New, Waxing Crescent, 1st quarter, Waxing Gibbous, Full, Waning Gibbous, last quarter, Waning Crescent).
(22): At what time of day must a full moon rise? At what time of day is a first quarter moon directly overhead? At what time of day day does a third quarter moon set? Be able to answer these three and similar questions with one of (sunrise, noon, sunset, midnight). Use a top view diagram of the Moon's orbit to help answer this question. (TQ #4)
(23): How often does the sun rise from a given location on the Moon? How often does the Earth rise from a given location on the Moon? For each question, answer with one of the following: (never, daily, every 27.3 days, every 29.5 days, yearly or never). (TQ #5)
(24): Explain the difference between the sidereal month and the solar month with the help of a simple diagram.
(25): What is a lunar eclipse? What is a solar eclipse? Explain why we don't have lunar or solar eclipses every time there is a full or new moon.
(26): Explain why some solar eclipses are annular and some are total.
(27): Given the equation of orbital velocity and the period equation, briefly explain how to use lunar observations to deduce the mass of the Earth.
(28): Given the inverse square law relationship between apparent luminosity, absolute luminosity and radial distance, be able to answer simple questions such as "Planet X is three times closer to the Sun than planet Y. How does the apparent luminosity of the Sun on X compare to the apparent luminosity on Y? Show your work."
(29): Be sure you understand what a spectrum is. What two things happen to the spectrum of an object as it is heated? Given two spectra, be able to identify which has a higher or lower temperature.
(30): Given the energy-wavelength relationship for light, be able to identify on a spectrum (graph of intensity vs wavelength) where the higher energy and lower energy regions are found.
(31): A greenhouse gas is defined as a gas that blocks infrared radiation. Use the laws of continuous radiation to explain why greenhouse gases result in a net warming of the Earth. As part of your answer, address the following point: Greenhouse gases block both incoming and outgoing radiation. Why don't these effects simply cancel each other out, leading to no net change in temperature?
(32): Based on Monday's film about the Greenhouse Effect, describe two methods scientists use to determine the global average temperature prior to recorded history.
(33): Ozone is an important gas in our atmosphere because it blocks out a substantial fraction of the incoming ultraviolet (UV) light from the Sun which would be harmful to most life on the planet. As a result of this property, would you expect the net effect of ozone to make the Earth warmer or cooler? Explain your answer. Note that I am not asking here about the so-called "ozone hole" problem but rather asking you to examine the logic of how the greenhouse effect works from a different perspective. (TQ #6)
(34): Based on your reading of Philosophy and the Scientific Method, answer the following: What is the difference between a scientific and a non-scientific belief? What is the major weakness of an irrefutable belief? (TQ #7)
(35): Explain how spectral absorption and emission lines are created. Given a simple energy level diagram for an atom, be able to state what energies of light can be emitted or absorbed.
(36): Explain why each different element has its own unique spectral fingerprint (what is a spectral fingerprint and how is it created?). How do we use this knowledge to determine the composition of other planetary atmospheres?
(37): Explain the concept of Doppler shift and the rules that govern it. Given a simple absorption-line spectrum, along with a comparison "rest" spectral fingerprint, be able to explain whether the source of the spectral lines is moving toward or away from us, slowly or quickly.
(38): How does the rotation of a planet affect spectral lines coming from the surface of that planet? Explain with the help of a simple diagram.
(39): If we were to observe a rapidly rotating planet "pole-on" (so that the axis of the planet's rotation were along our line of sight), how would the Doppler shifts coming from the surface of the planet compare with the "edge-on" case discussed in class and in question 38? Explain. (TQ #8) - *
(40): Name and briefly explain the four major functions of a telescope.
(41): Given the formula for resolution, be able to explain why large aperture telescopes have better resolution and why radio telescopes, despite their gigantic apertures, have poor resolution compared to optical telescopes.
(42): Explain "seeing". What causes stellar images to appear blurred when we look at them through ground-based telescopes?
(43): Explain how interferometry works to improve the resolution of a system of individual radio telescopes.
(44): Explain why stars twinkle and planets do not.
(45): Given the proportionality that relates density to mass and size (radius), be able to solve simple problems such as "Planet A has four times the mass and twice the size (radius) of planet B. Numerically, how does the density of planet A compare to the density of planet B? Show your work."
(46): Given the approximate densities of the four main components of the solar system (metal, rock, ice and gas), be able to explain how we can deduce the composition of a planet simply by knowing its mass and size.
(47): What is the Kuiper Belt? What are the arguments against Pluto being classified as a planet? A good starting place to answer these questions is the Kuiper Belt information page at the nine planets website: http://seds.lpl.arizona.edu/nineplanets/nineplanets/kboc.html. (Alternate mirror sites for the same Kuiper Belt information are here and here in case the first link doesn't work) Also, David Jewitt has an excellent Kuiper Belt web page: http://www.ifa.hawaii.edu/faculty/jewitt/kb.html. Check out the "Pluto and Pluto Express" page there and the "Plutinos" page for more about the Pluto debate. (TQ #9)
(48): Briefly explain the capture hypothesis for the origin of the solar system. Explain how the properties of the planetary orbits tend to refute this hypothesis.
(49): Briefly explain the catastrophe hypothesis for the origin of the solar system. Given the size of stars, typical speed of stars relative to one another and typical distance between stars, explain why this hypothesis is unlikely to be true.
(50): Explain why the initial cloud of gas and dust (the solar nebula) collapses into a disk shape as opposed to a small spherical object.
(51): Given the condensation temperatures for the four main components of planets (metal, rock, ice and gas) and an indication of the temperature in various parts of the solar nebula disk, be able to identify and explain which components you would expect to condense into solid form at various locations in the solar system.
(52): What is self-gravity? Given the formula for self-gravity, use it to explain why the collapse of the solar nebula accelerated as the size of the nebula shrank after the initial triggering event in the nebular hypothesis. Given the relative mass and size of two objects, be able to state which has stronger self-gravity (i.e. "Cloud A has the same mass as Cloud B, and Cloud A is 10 times larger than Cloud B. Which has stronger self-gravity?")
(53): Based on the film we saw in class on Monday, October 2, what are the two main obstacles that renewable energy sources must overcome in order to become viable alternatives to fossil fuel energy?
(54): Although human emissions of Carbon Dioxide (CO2) are small relative to natural sources of CO2 emissions, studies in the last century show that the increase in global atmospheric CO2 has been caused by human activity rather than a fluctuation in natural activity. Read part 1 of the following article (from a scientific discussion group on the internet): http://www.radix.net/~bobg/faqs/scq.CO2rise.html and explain in 1-2 sentences how Carbon isotope evidence is used to show that the global increase is related to human rather than natural activity. (TQ #10)
(55): One potential consequence of global warming will be a relatively fast rise in sea levels as a result of melting ice (mainly in West Antarctica, since it is currently on land) and one other mechanism, described in the first few paragraphs of the following scientific discussion summary: http://www.faqs.org/faqs/sea-level-faq/. Read these paragraphs and summarize in a sentence or two another mechanism besides melting ice that may cause sea levels to rise as the Earth warms up. (TQ #11)
(56): Given the equation for escape velocity, be sure you understand what quantities do and do not affect the escape velocity. For example, if Jupiter were any closer to the Sun, would its escape velocity be any different? Explain.
(57): Know and explain the relationship between the mass of a typical gas particle and the velocity of a typical gas particle. Know and explain the relationship between temperature and the velocity of a typical gas particle.
(58): Name and explain two reasons why the Earth cannot accumulate Hydrogen gas while Jupiter can. Given the initial composition of the solar nebula, use your two reasons to help explain why the Earth's composition is so different from the initial solar nebula composition.
(59): Name and explain three reasons why Jupiter is so much larger than the Earth.
(60): Explain why we believe Uranus and Neptune are so much less massive than Jupiter and Saturn, despite the fact that the two outermost planets presumably formed under conditions (colder temperatures, larger feeding zones) that were even more favorable to larger masses
(61): Use a graph of continuous radiation for the Sun and a planet like Jupiter to help explain why direct imaging of other planetary systems in visible light is probably hopeless and why there is some hope in the idea of infrared imaging (if the resolution problem can be overcome).
(62): Explain how we use Doppler shifting evidence to deduce the existence of planets around other stars.
(63): Explain why searches for other planetary systems so far have been biased in favor of discovering short-period planetary companions and high mass planetary companions.
(64): Suppose that instead of viewing a planetary system edge-on, the system is tilted a little bit with respect to our line of sight. In guessing the mass of the planetary companion, however, we *assume* that the system is being seen edge-on. Would our assumed planetary mass be larger, smaller or the same as the true planetary mass? Explain. (TQ #12)
(65): Visit NASA's TPF web site to learn about the Terrestrial Planet Finder mission, and answer the following question: Suppose two terrestrial-sized planets are discovered such as Earth (where life is possible and abundant) and Venus (where no life exists and the environment is much too hostile). What spectral features of these two planets will be similar? What will be different (thus enabling us to distinguish terrestrial planets where life might be present)? (TQ #13)
(66): What is differentiation? How does it help explain the current organization of the Earth's interior (metal core, rocky mantle)?
(67): Explain the heat source that made the early, forming Earth so hot that it was completely molten throughout. What is the current heat source that keeps Earth's interior partially molten?
(68): What is a half-life? Be able to work your way through an example of a radioactive parent isotope sample as it decays into stable daughter atoms. For example, "The half-life of a parent is 100 years. The original composition is 300 parents and 100 daughters. The current composition is 150 parent atoms. How old is the rock, and how many daughter atoms are present?"
(69): Describe how stable isotope siblings of parents and daughters are used to determine the original composition in a rock. For example, "When a rock solidifies, the number of parent atoms is one-half the number of stable sibling atoms. The parent has a half-life of 10,000 years. The current composition is 20 parents, 640 daughters and 640 stable siblings. How old is the rock, and what was the rock's original composition?"
(70): Explain how the Earth's magnetic field interacts with the solar wind to both protect life on Earth and create the aurorae visible in the atmosphere near the North and South polar regions.
(71): Briefly explain the concept of sources and sinks in the Carbon cycle. Give at least two examples of sources and two examples of sinks. How is human activity altering the Carbon cycle?
(72): Read http://earthsky.com/2000/es000226.html to find out the basics about the Faint Sun Paradox and summarize it in 1-2 sentences. (TQ #14)
(73): Describe the two different possible sources for all of the liquid water that covers the Earth's surface today.
(74): Argon gas is called a "tracer" because it is one of the few gases in our atmosphere that maintains its original abundance from the original (primitive) atmosphere to the modern (secondary) atmosphere. What two properties of Argon gas make this possible? Explain why each one is important.
(75): What is the ozone layer, and why is it important for life on Earth? Explain how the production of Chloroflourocarbons (CFC's) results in the partial destruction of Earth's ozone layer (minor correction from class: it is the Chlorine atoms rather than the CFC molecules that are responsible for the ozone loss, the Chlorine atoms originate from CFC molecules broken apart by sunlight).
(76): Read the EPA's web pages about ozone at http://www.epa.gov/ozone/science/science.html to answer the following question. Briefly explain three reasons why the ozone depletion largely occurs over the Antarctic each year rather than uniformly in the rest of the Earth's atmosphere. (TQ #15)
(77): Explain why the Earth has two tidal bulges as a result of the Moon's gravity.
(78): What is the difference between spring tides and neap tides? Which type of tides should we expect to see during new moon? Full moon? 1st quarter? Explain.
(79): Why does the near tidal bulge "lead" the Moon in its orbit around the Earth? If the Earth weren't rotating, how would this situation change?
(80): Explain how the Earth's rotation, combined with the tidal bulges from the Moon, result in the Earth's rotation slowing down and Moon's orbital distance from the Earth slowly increasing over time.
(81): Explain why the time between the lowest tide and the highest tide is always a little bit longer than six hours. What if the Moon's orbital velocity were faster or slower? How would the time between high and low tide change? Explain.
(82): Explain the concept of tidal locking and how this effect explains the fact that the same face of the Moon always points at the Earth.
(83): Explain how we know, simply from estimating the Moon's mass and radius, that it is a very small metallic core relative to the Earth.
(84): Why doesn't the Moon have an atmosphere like the Earth?
(85): The average temperature on the Moon is about zero degrees Fahrenheit while the average temperature on Earth is about 60 degrees. Explain how we know this difference is due to the greenhouse effect (as opposed to, say, a difference in the Earth-Sun vs the Moon-Sun distance).
(86): Explain how the maria on the Moon formed and why their appearance differs from that of the lunar highlands.
(87): The solidification age of the maria (based on samples brought back by the Apollo missions) is about 3.8 billion years. For the highlands, it is about 4.2 billion years. If the cratering rate on the Moon were constant over time, how would you expect the crater density in the highlands to compare to the maria? Explain.
(88): How does the crater density between the two regions *actually* compare? Explain what this implies about the cratering history of the Moon. Why can't we see a similar story in the Earth's crust?
(89): Although the Moon has no atmosphere, recent missions surveying the lunar surface have revealed the presence of water-ice on the Moon's surface. Read http://nssdc.gsfc.nasa.gov/planetary/clementine.html, a web site with detailed results of the Lunar Prospector and Clementine missions, and explain how it is possible that water-ice has survived on the Moon for all these billions of years without sublimating away and escaping. (TQ #16) (this is the last of the thought questions to appear prior to exam #2 ... honors homework #2 is due Wed Oct 25, honors paper due Mon Oct 30)
(90): What is an isotope fingerprint? How do we use isotope fingerprints to argue that the Earth's mantle and the Moon both originated from the same source material?
(91): What are volatiles? The Moon has a lower abundance of volatiles than the Earth's mantle. What does this fact imply about the history of the material that formed the Moon, compared to the history of the material that formed the Earth's mantle?
(92): Explain how the presence of volatile elements in the planets argues against the catastrophe hypothesis for the origin of the solar system.
(93): Explain the capture theory of the Moon's formation in a sentence or two. Explain why this theory has problems explaining the rock/metal ratio in the Moon compared to the Earth and the isotope fingerprints of the Earth's mantle and the Moon.
(94): Explain the Co-Creation theory of the Moon's formation in a sentence or two. Explain why this theory has problems explaining the rock/metal ratio in the Moon.
(95): Explain the Fission theory of the Moon's formation in a sentence or two. Explain why this theory successfully predicts the rock/metal ratio in the Moon and the isotope fingerprint similarity between Earth and Moon.
(96): Why does the Fission theory have trouble explaining the difference in abundance of volatiles in the Earth and Moon? Also, explain how the current (relatively slow) rotation of the Earth is a problem for the Fission hypothesis.
(97): Explain the Giant Impact theory of the Moon's formation in a sentence or two. Explain why this theory successfully predicts the rock/metal ratio in the Moon, the isotope fingerprint similarity between Earth and Moon, and the relative lack of volatiles on the Moon compared to the Earth.
(98): Some scientists are wary of the Giant Impact theory because it does not really qualify as a falsifiable theory. Explain what falsifiable means and why a scientific theory should be falsifiable (you may wish to revisit relevant sections of the Philosophy and the Scientific Method reading from the Physics 20073 home page).
(99): How do we know that Mercury is mostly made of metal, rather than an even mix of rock and metal like the other terrestrial planets?
(100): In 1-2 sentences each, describe two different formation theories that explain Mercury's high density relative to the other terrestrial planets. For help, you may wish to refer to the "Science" section of http://sd-www.jhuapl.edu/MESSENGER/, a web site detailing one of NASA/JPL's upcoming missions to Mercury, although I mentioned two theories in lecture which may be in your notes. (TQ #17)
(101): We know that magnetic fields are formed by moving charged particles. Explain what scientists believe are necessary properties for a planet to have a magnetic field. Explain each property in terms of the initial statement about magnetic fields. Use your reasoning to explain why some scientists did not anticipate Mercury would have a significant magnetic field.
(102): What are two pieces of evidence that indicate Mercury's interior is at least partially molten? Explain each one.
(103): What is Crater Retention Age (CRA)? Explain how we use the concept of CRA to state with some confidence that Mercury's surface age is likely somewhere between that of the lunar maria and lunar highlands.
(104): Name and explain two reasons why Mercury has no significant atmosphere.
(105): Although Venus is about the same size, mass and density as Earth (and thus has a similar level of internal heating and geological activity), Venus has no significant magnetic field. Explain why, in the context of your reasons given in question 101.
(106): Explain how the craters on Venus differ from craters found on Earth. First, explain how we use the concept of Crater Retention Age to estimate the solidification age of Venus' surface to be about 500 million years. Second, craters on Venus all tend to have a pristine appearance compared to craters on the Earth. Explain why this difference exists.
(107): Explain the evidence that implies Venus suffered some sort of catastrophic event about 500 million years ago that essentially resurfaced the planet.
(108): Although we have seen to direct photographs of active volcanism on Venus today, studies of Venus' atmosphere over time have given a good indication that volcanoes are active all over the planet. Explain this evidence.
(109): Although Venus started with an atmosphere that was probably very similar in mass and composition compared with the Earth, the slightly higher temperatures on Venus combined with its closer proximity to the Sun, led to a gradual loss of water vapor on Venus. Explain why.
(110): Use an analysis of the Carbon Cycle to explain why less water on Venus ultimately leads to a positive feedback loop (known as the runaway greenhouse effect) increasing the temperatures (and thus further decreasing water levels) even more.
(111): How does the total mass of Venus' atmosphere compare with the total mass of Earth's atmosphere, and how does the runaway greenhouse effect explain this difference?
(112): How does the original mass of Venus' atmosphere compare with the original mass of Earth's atmosphere? Explain how and why scientists use Argon to "reconstruct" the original atmosphere of Venus and guess that it was once very similar to Earth. If Venus had twice as much Argon today as the Earth, what would we then assume about Venus' original atmosphere? Explain.
(113): Argon reconstruction cannot work for all planets. For example, Mercury has zero Argon in its atmosphere today, yet scientists do not go on to assume that Mercury has never had any atmosphere whatsoever. Explain why Mercury is treated differently from Venus.
(114): What is Deuterium? What is heavy water? What is the difference between heavy water and normal water? How does the heavy water/normal water ratio on Venus compare to that of Earth? How does is this difference explained by the runaway greenhouse effect?
(115): An alternative explanation for the lack of water on Venus is that the water was absorbed into the crust somehow and now resides below the surface in aquifers or underground lakes. Explain how the heavy/light water ratio tends to argue against this hypothesis.
(116): Another alternative explanation for the lack of water on Venus is that Venus never had much water to begin with, compared to the Earth. Explain how Argon reconstruction or the heavy/light water ratio both tend to argue against this hypothesis.
(117): Name and briefly explain two reasons why a simple analysis of the solar nebula theory would leave one to believe that Mars should be more massive than the Earth (in actuality, it is only about 10% of Earth's mass thanks to the effects of Jupiter disturbing its formation).
(118): Explain why Astronomers didn't believe Mars should have a significant magnetic field (it has no significant magnetic field). Explain the evidence that Mars should have a significant magnetic field.
(119): The film we saw on Wednesday, November 8 dealt with in part the discovery of extrasolar planets. These Jupiter-sized objects at distances of less than 1 AU from their parent star pose problems for the solar nebula theory of planetary formation. Read the following article from Scientific American: http://www.sciam.com/1196issue/1196scicit1.html. One possible explanation for these large planets being so close to their parent stars is that they formed at large distances (5+ AU, where it was cold enough and the feeding zone was large enough for large planets to form) and then spiraled inward (via a complex gravitational interaction with the surrounding disk of gas and dust). According to Lin's theory, what are two possible mechanisms that made these planets stop spiraling inward rather than just plunging into their parent stars? Explain each in 1-2 sentences. (TQ #18)
(120): During the lecture on Friday, November 10, we looked at an image of Mars taken from the Pathfinder probe, showing a yellow-pink Martian sky. Read the following article from NASA about atmospheric color: http://www-mgcm.arc.nasa.gov/mgcm/faq/sky.html. Explain in 1-2 sentences what gives the Earth's atmosphere its blue color. Next, briefly state the one significant difference between Earth's and Mars' atmosphere that gives Mars its color (without this difference, Mars' sky would look blue like Earth's). (TQ #19)
(121): Explain why Olympus Mons is so much larger than the largest mountains on Earth or Venus.
(122): Explain the mechanism behind the global dust storms that periodically cover the Martian surface. Why don't similar storms happen on Earth?
(123): The Martian atmosphere today has about 1% of the mass of Earth's atmosphere. Explain how Argon reconstruction seems to imply the original mass of the Martian atmosphere was also about 1% of the mass of the Earth's atmosphere.
(124): What evidence on Mars argues that the Martian atmosphere was once much warmer and more similar in mass (and thus, atmospheric pressure) compared to the Earth? Explain.
(125): Explain the "freeze out" theory that may have led to the loss of the Martian atmosphere. Specifically, explain what triggered the beginning of this process and how this process gradually leads to a colder atmosphere which causes the water to condense into solid ice on (or under) the surface (the "freezing out" part).
(126): Explain how the Argon levels in the current Martian atmosphere combined with the evidence that Mars once had a thicker atmosphere (from q 124) argues against the "freeze out" theory.
(127): How does the 36-Ar/40-Ar ratio on Mars compare to Earth? Why is this comparison seen as evidence that the original Martian atmosphere escaped rather than freezing out?
(128): How does the "giant impact" theory propose to explain the loss of the Martian atmosphere? Explain the evidence on Mars that contradicts the giant impact theory.
(129): How does the "impact erosion" (IE) theory propose to explain the loss of the Martian atmosphere? Why does the IE process occur on Mars and not on Earth, according to the theory?
(130): Explain the prediction the IE theory makes about the crater retention age (CRA) and the solidification age of the Martian surface relative to the lunar surface.
(131): Explore the following web site from NASA's Goddard Space Flight Center about the Martian meteorites: http://rsd.gsfc.nasa.gov/marslife/marsmet/. Based on the information found here, answer the following: What conclusive evidence shows that these meteorites are from Mars? Why aren't these meteorites red like the Martian surface soil? (TQ #20)
(132): Why is it scientifically important to determine whether or not life once existed on Mars?
(133): Why is it so easy to find meteorites in Antarctica? What are meteorite families? How are meteorites from different families distinguished from one another? What is a parent body?
(134): Initial soil tests from the Viking lander seemed to indicate the presence of life on Mars. Describe the control experiment used to show that these initial positive results were probably false.
(135): Jupiter's composition is mostly Hydrogen and Helium like the Sun. Why is Jupiter's composition so different from the Earth's composition?
(136): Why is Jupiter's magnetic field so much stronger than Earth's? As part of your answer, explain why much of the Hydrogen in Jupiter is in liquid or molten form (in which it behaves like a metal).
(137): Besides radioactive decay, Jupiter has another large heat source. Explain how the contraction of Jupiter generates heat.
(138): Explain the origin of the bands on the visible surface of Jupiter.
(139): Tonight (Friday, November 17) sometime after midnight, Astronomers expect to see the peak of the annual Leonid meteor shower. You can watch it, too, by looking in the general direction of the constellation Leo (easy to find tonight since the 3rd quarter moon is in Leo, but unfortunately, that will make it tougher to see faint meteors) in some dark area well outside the city (find a dark southeastern horizon). Find out more information about the Leonid Meteor Shower on the web and answer the following: What exactly *is* a meteor shower? Where does it come from? And why is the Leonid Meteor Shower extremely spectacular about every 33 years or so instead of every year? (TQ #21)
(140): Although Io is similar in many ways to Earth's Moon, it orbits much more quickly around Jupiter (once every 40 hours as opposed to the Moon's 27.3 day sidereal period). Use the equation of orbital velocity to explain why and the period equation to explain why.
(141): Although Io has about the same size and (roughly) the same composition as Earth's Moon, Io is incredibly active geologically. Explain what causes this.
(142): Explain why tidal flexing might also be a source of heat for Mercury.
(143): What causes Io's plasma "tail"? Why does Io's "tail" precede Io's orbital path?
(144): Although Europa is completely covered by ice (giving it the highest albedo of any object in the solar system), we know that it is mostly rocky. Explain how we know this.
(145): Why do we think life might exist on Europa? As part of your answer, explain why we think liquid water is present beneath the surface of Europa and what the mechanism is that keeps the temperature warm enough on Europa for liquid water to exist.
(146): Visit NASA's Galileo mission web site at http://www.jpl.nasa.gov/galileo/ and use the information gained from the web site to answer the following: Three of Jupiter's four large moons (Europa, Ganymede and Callisto) show very faint traces of an Oxygen atmosphere. What is believed to be the source of this Oxygen (it isn't biological, apparently)? (TQ #22)
(147): Ganymede is covered with ice, like Europa, but it has regions that appear relatively dark and light. Explain what causes these discolorations in the ice. How does the age of a darker region compare to the age of a lighter region? Why is Callisto's surface darker than Ganymede's? Explain.
(148): Explain why the Co-Accretion theory is favored as the origin of Jupiter's moons. How does this theory explain the differences in density and size for Jupiter's moons?
(149): Explain how we use stellar occultations to study the composition and motion of ring systems of the outer planets.
(150): What is a rotation curve? How is this used to determine the nature of the rings of Saturn? What would the rotation curve of Saturn's rings look like if they were one solid object? How does the real rotation curve differ from this? Explain.
(151): How do we know that Saturn hasn't always had a ring system? Explain the process by which we think Saturn acquired a ring system (as part of your answer, explain what the Roche Limit is).
(152): Explain why Saturn's moon Titan has an atmosphere while Jupiter's moon Callisto (similar in size, density, composition) does not.
(153): What accounts for the color difference between Jupiter and Neptune?
(154): Explain why some Astronomers thought Neptune's moon Triton might have an atmosphere like Saturn's moon Titan. Why do we think Titan formed an atmosphere while Triton did not? As part of your answer, explain the evidence that leads us to believe Triton formed under very different conditions than Titan and how that explains the difference between the two moons.
(155): Explain the mechanism that causes Triton to spiral in toward Neptune. What will be its eventual fate (answer in terms of question 151)?
(156): Explain how impacts may help us understand why the moons of giant planets are generally larger the further away they are from their parent planet.
(157): Hundreds of tons of interplanetary dust falls to the Earth every day. Experiments to study this dust have shown that it can be divided neatly into two groups. The first group strikes the Earth's upper atmosphere with relatively low speed, and the second group strikes with a very high speed. Which type of dust (asteroidal in origin or cometary in origin) is more likely to be the high speed dust? Explain why. (Hint: see question 156.) (TQ #23)
(158): What is the Kuiper Belt? What is the Oort Cloud? Besides the difference in average period, what is the other major difference between long-period and short-period comets. What does this difference tell us about the difference in shape of the Kuiper Belt and the Oort Cloud?
(159): Why do comets have two tails? Explain the behavior of the gas tail and the dust tail.
(160): Why is it that the best time to observe a meteor shower is between midnight and dawn? (Hint: Your book has a pretty good diagram and explanation of this.) (TQ #24)