1. The planet Neptune is the most distant planet…


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20.50

1. The planet Neptune is the most distant planet that we have studied so far. The semi-major axis of its orbit is approximately 30 AU, that is, it is 30 times farther from the Sun than the Earth. a. Using Kepler’s third law, calculate how long it takes for Neptune to orbit the Sun once if its semi-major axis is exactly 30 AU. b. Neptune was discovered officially in the year 1846. Has it completed an entire orbit of the Sun since its discovery? How many times, approximately, has Mars orbited the Sun since Neptune was discovered? c. What does this suggest the seasons may be like on distant planets like Neptune? For example, how long does winter last? 2. The Voyager satellites visited all of the gas giant planets in our Solar System and for many years much of our understanding of these planets and their moons came from the Voyager experiments. In the case of Jupiter, our understanding increased when the Galileo mission reached the planet in 1995. In 2004, the Cassini Mission arrived at Saturn, and although this mission is only beginning, we have already learned a great deal about Saturn. a. Research some of the recent results from the Cassini mission on the planet Saturn or any of its moons. Contrast what Cassini has learned to what we knew prior to this Mission. b. Describe the Huygens probe that landed on Saturn’s moon Titan and briefly describe some of its findings. 3. We have found that Saturn is not the only outer planet with rings; Jupiter, Uranus, and Neptune all have ring systems. a. Do we think the ring systems surrounding these planets are as old as the planet? Why or why not? b. Do we expect that inhabitants of Earth 100 million years from now will see the same ring systems around these planets as we do now? Why or why not? c. Describe the processes that determine the evolution of rings around giant planets. 4. Although the Kuiper Belt and the Oort Cloud were both proposed long ago, the first large objects (e.g., Quaoar, Varuna, and Sedna) that are in these regions of the Solar System were only discovered recently. a. What are the properties that prevent these objects from being easily observed? b. Why is it considered likely that there may be other Pluto-sized objects in these two regions that have not yet been discovered? 5. When comets get close to the Sun, they are observed to have long, bright tails. These can be bright enough to be seen by the naked eye from Earth. a. What are comets like when they are on the part of their orbit that is far from the Sun? Are they as easy to observe? b. Are all comets likely to survive their trip around the Sun? Why or why not? 6. Many meteorites have been recovered on Earth. These are the remnants of meteoroids that have penetrated the Earth’s atmosphere and landed on the Earth. a. Why are these recovered objects interesting to scientists? What can they tell us about the Solar System? b. What was discovered in the famous “Martian Meteorite” (also known as ALH84001) that led some scientists to suggest that it included evidence for life on Mars? Is this evidence still considered firm? What alternative explanations for the unique formations seen in this meteorite can you propose? (See for example the link to the APOD: Martian Meteorite image of this meteorite.)

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