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Download Physics 127 Descriptive Astronomy Homework #8 Key (Chapter 4
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Transcript
Physics 127 Descriptive Astronomy Homework #8 Key (Chapter 4) Winter 2015 4-1. What are the two agreed upon defining characteristics of a planet? The two defining characteristics or a planet are: (1) It is a (non-stellar) object orbiting a star. (2) It is sufficiently massive that its gravity has shaped it (approximately) into a sphere. 4-2. Compare the characteristics of a terrestrial planet to those of a Jovian planet. A table is an efficient way to summarize the most obvious differences: Characteristic Location Temperature Composition Relative Size Rings? Moons Rotation Density Atmosphere Surface Associated Debris Class Members (descending size order) Terrestrial Planets Inner solar system Warm to hot Rocky Small No Few to none Slow (P ~ days) High (𝜌 ~ 3.3 𝑡𝑜 5.5 g/cm3 ) Thin (CO2, N2, O2) Cratered/Volcanic/Mountainous Asteroids Earth, Venus, Mars, Mercury, Moon Jovian Planets Outer solar system Cold to very cold Gaseous (mostly H and He) Large Yes Many Fast (P ~ hours) Low (𝜌 ~ 0.7 𝑡𝑜 1.7 g/cm3 ) Thick (H2, He, CH4, NH3) Gaseous, not well-defined Kuiper Belt, Comets Jupiter, Saturn, Uranus, Neptune 4-6. What are the asteroid belt, the Kuiper belt, and the Oort cloud? Where are they located? How do the objects found in these three regions compare? These are three groups of debris in the solar system, mainly solar nebula material that did not coalesce into planets or their moons. The asteroid belt is a belt of rocky debris, mainly confined to a region between the orbits of Mars and Jupiter and roughly confined to the ecliptic plane orbiting about the sun in the same direction as the planets. The Kuiper belt is a belt of icy objects with rocky impurities, also roughly in the ecliptic plane, orbiting in the same direction as the planets and asteroids, beyond the orbit of Neptune. The Oort cloud is a much larger cloud of icy debris with rocky impurities well outside the Kuiper belt. It is thought to be roughly confined to a thick spherical shell, and not confined to the ecliptic plane. 4-8. What is the connection between comets and the Kuiper belt? What is the connection between comets and the Oort cloud? Most, perhaps all, comets are believed to be objects that either originated in the Kuiper Belt or the Oort cloud, the orbits of which now penetrate the inner solar system. Most Kuiper Belt comets are believed to be fragments produced in collisions between Kuiper Belt objects. These typically have periods of thousand to tens of thousands of years. Oort cloud comets are believed to have been perturbed into elongated orbits by passing stars. Typical periods are millions of years. Both comet types are made primarily of ices and embedded dust and rocks.