Advice for submitting study guide answers is here. Updated through Monday, October 21.

(47)

Briefly explain the catastrophe hypothesis for the origin of the solar system. Explain two misconceptions we had about the nature of the universe that led us to believe this theory was originally plausible.

(48)

Name and briefly explain two arguments that contradict the catastrophe hypothesis for the origin of the solar system.

(49)

Briefly explain the capture hypothesis for the origin of the solar system, and explain two assumptions scientists made about the nature of the universe and space itself that made the capture hypothesis seem plausible at the time.

(50)

Name and briefly explain three arguments that tend to contradict the capture hypothesis.

(51)

From your textbook's chapter 7.1, what are TNO's? Where are they found in the solar system? About how many have been discovered? (HW)

(52)

From your textbook's chapter 7.1, briefly explain how the scientific community decides on the rules for naming newly discovered things (whether they are dwarf planets, moons, surface features, asteroids, etc). Not asking about the rules for each separate thing, just how we decide on the rules in general. (HW)

(53)

From your textbook's chapter 7.4, the authors note that there are many "exceptions to the rule" in the solar system, such as Uranus tilted all the way over on its side or Venus spinning backwards. Name and briefly explain what part of our theory of planetary formation can help explain these odd planetary properties? (HW)

The following four homework questions are from the article "What Is a Planet?" from the January 2007 issue of Scientific American. You can find a copy of this article on the Physics 10273 course shell in TCU's brightspace.

(54)

According to the International Astronomical Union (IAU), what is the official definition of a planet now and why does this definition exclude Pluto from having the status of a planet? (HW)

(55)

It was once thought our solar system had over 20 planets before the definition of planet was last modified in 1852. Explain what all of these extra planets were and why they were demoted from planet status. (HW)

(56)

The authors propose an improvement of the definition of planets based on a factor represented by the greek letter mu. What is "mu"? (HW)

(57)

Some astronomers argue that planets should be defined only by their intrinsic properties (such as size, shape or composition) rather than by their location or surroundings. What is the authors' counterargument to this idea? (HW)

(58)

During the collapse of the solar nebula cloud, explain why the temperature of the solar nebula increased as the cloud collapsed.

(59)

Explain why the initially slowly spinning cloud spun faster as the cloud collapsed. As part of your answer for this last part, define "angular momentum" and explain its role in this process.

(60)

Explain why the large, roughly spherical solar nebula collaped into a disk shape rather than just a smaller sphere. A diagram would help but is not necessary if your explanation is sufficiently detailed.

(61)

Explain what primitive meteorites are and how they differ from ordinary meteorites. Explain how evidence found in primitive meteorites tends to confirm our ideas about the accumulation phase of the origin of the solar system.

The following five questions are from the article "Secrets of Primitive Meteorites" by Alan E. Rubin from the February 2013 edition of Scientific American. You can find a copy of this article on the Physics 10273 course shell in TCU's brightspace.

(62)

Describe the general structure and appearance of chondrites. What makes them important to astronomers studying the early solar system and planetary formation? (HW)

(63)

On what basis does the author conclude that Enstatites like formed closer to the Sun than most other groups of chondrites? (HW)

(64)

The author asserts that ordinary chondrites, the most common type of chondrite, likely existed just sunward of the center of asteroid belt. Explain his reasoning. (HW)

(65)

Explain why the author believes that carbonaceous chondrites likely existed furthest from the Sun compared to any other type of chondrite. (HW)

(66)

Explain how and why chondrites that existed in a very dusty part of the solar nebula differ in appearance from other types of chondrites. (HW)

(67)

Name and briefly explain three reasons why Jupiter is so much larger than the Earth. As part of your answer, be sure to explain both ways in which ice particles make it easier for larger planets to form.

(68)

Name and explain two reasons why the Earth cannot accumulate Hydrogen gas while Jupiter can. One has to do with temperature, the other with escape velocity.

(69)

Why does the Earth have a hard time capturing Hydrogen while easily maintaining an abundance of gases like Carbon Dioxide? As part of your answer, explain why gas velocity is higher from lighter gases.

The following two questions come from the Kepler Mission FAQ. The Kepler mission is the NASA mission searching for extrasolar planets transiting their parent stars that we have discussed in class.

(70)

Name and briefly explain two reasons why Earth-size planetary transits must be observed from space rather than from ground-based telescopes. (HW)

(71)

How can the Kepler mission tell the difference between a variation in brightness caused by a planetary transit compared to a variation caused by, for example, a sunspot moving across the star or a cycle of high/low stellar activity (such as the "Maunder minimum" cycle observed on our Sun)? (HW)

(72)

From your textbook's chapter 21.4, explain the discovery that made astronomers Didier Queloz and Michel Mayor famous. It's not been updated in the book yet, but these two won the Nobel Prize for their discovery on October 7 of this year. (HW)

(73)

From your textbook's chapter 21.4, explain how we deduce the approximate size (or radius) of transiting exoplanets? Also, how do we deduce the density of these exoplanets in order to determine whether they are rocky or gaseous? (HW)

(74)

From your textbook's chapter 21.4, explain why it wasn't until the 4th year of Kepler spacecraft observations that we were finally able to discover exoplanets with orbits like the Earth that require at least 1 year to orbit their parent star. (HW)

(75)

From your textbook's chapter 21.4, explain why it is easier to use the infrared part of the spectrum (instead of the visible part) in order to directly image planets orbiting around other stars. (HW)

The following two questions are from a short online Scientific American article called "The Earth Next Door", available at http://www.scientificamerican.com/article/the-earth-next-door/. Read the article and answer the following questions:

(76)

What is Proxima Centauri and how does it relate to Alpha Centauri? What are the properties if Proxima's suspected planet, Proxima b (estimated mass and orbital period)? (HW)

(77)

Proxima b is so close to its parent star, why do we think it may have liquid water present on its surface? Name and briefly explain three potential problems Proxima b might have due to its close orbit that may prevent the planet from providing a stable environment in which to host life? (HW)

(78)

Know the rules of Doppler shifting. Be able to explain with a simple diagram the difference between radial and transverse velocity.

(79)

In the Doppler wobble technique, what do we measure initially (what do we plot on the graph)? What two properties of the star's motion do we measure from the wobble graph (show on the graph of explain how we find these)?

(80)

What two properties of the companion planet do we deduce from this information in question 79, and how are the planet's properties related to each of the two properties of the star's motion we measure?

(81)

Explain why our searches for exoplanets are (a) biased in favor of companion planets with large masses (Jupiter-class or higher) and (b) biased in favor of companion planets that are very close to their parent star (most closer than Earth is to our Sun).

(82)

Is it fair to say that "hot Jupiter" systems are the majority of existing planetary systems and that our basic theory of planetary formation (that says gas giants should usually be found far from their parent stars) incorrect? Explain why or why not.

(83)

Explain why we cannot necessarily believe that indirect observations of planetary companions via Doppler wobbling are truly planetary companions. Are our assumed companion planet masses higher or lower than true planet masses in tilted systems? Explain with the help of a diagram showing a tilted vs edge-on case.

(84)

Explain the details and significance of the discovery of an eclipsing (or transiting) extrasolar planetary system. Why was this kind of system so important to find in light of the uncertainty in Doppler wobble measurements?

(85)

From your textbook's chapter 21.5, what is the mass range of the most common type of exoplanet discovered by the Kepler mission? Why do the authors suggest the planets less massive than this range are perhaps even more common, even though the Kepler mission did not report finding many? (HW)

(86)

From your textbook's chapter 21.5, notice figure 21.25. The blue curve mapping the predicted size of a mostly Hydrogen planet goes up as mass goes up, at least until you look at planet masses that are more than about 1000 times Earth's mass, at which point the more mass you add to a planet, the *smaller* the planet gets. Explain why this happens for very massive planets. (HW)

(87)

From your textbook's chapter 21.6, explain how astronomers think hot Jupiters form differently from the way we think our planet formed. (HW)

(88)

From your textbook's chapter 21.6, explain why astronomers think Uranus and Neptune likely did not form at their current distances from the Sun but instead somewhat closer in. Also, how do we think Uranus and Neptune moved from their original orbital distances to the current, more distant orbits? (HW)

(89)

From your textbook's chapter 30.1, explain what is the Copernican Principle, and provide at least two historical examples that have motivated scientists to believe this is a valid idea. (HW)

(90)

From your textbook's chapter 30.1, explain what is the Fermi Paradox and how it is related to the Copernican Principle. (HW)

The following three questions come from the Scientific American article "Alone in the Milky Way" (Feb 2018):

(91)

The author makes an argument that, assuming life is common in the galaxy, Earth is likely one of the first planets in the galaxy to host life. Explain why (this is related to the concept of metallicity, so include a definition of that term). (HW)

(92)

According to the author, we live in a galactic "habitable zone": not too close to the center and not to far away. Explain why life is less likely to appear and/or thrive on (a) planets closer to the center of the Milky Way galaxy (two reasons) and (b) planets further from the center of the Milky Way galaxy. (HW)

(93)

The presence of Earth's large moon has allowed our planet to distinguish itself from Venus in ways that are favorable for the existence of life. Explain (a) how the origin of our Moon led us to have a thin crust enabling plate tectonics and (b) how it is aided in the development of the magnetic field that protects our atmosphere (and us) from harmful cosmic rays. (HW)

(94)

What are the three ingredients necessary for life? What is a possible source for each ingredient?

(95)

On the 5-km highway of time representing the history of Earth, what length accurately reflects all of recorded human history?

(96)

Critics of evolution wonder how a process based on random chance could result in extremely complex organisms. How do biologists respond to this argument?

(97)

What discovery did the Magellan spacecraft make about the recent geological history of Venus?

(98)

What recent evidence discovered in Antarctica implies that life may have once existed on Mars?

(99)

What is the habitable zone? Explain how recent discoveries of life in extreme environments (e.g. black smokers, worms in methane ice, etc.) has affeted our view of a habitable zone. What is a "gravitational" habitable zone?