Formation of the Solar System - Tamalpais Union …



Formation of the Solar SystemAstronomyName:Period:Any model of the formation of the solar system must account for the motions, compositions and locations of all the planets and their moons. In this lab, you will use the motions of objects in the solar system to concoct a model of the formation of the solar system. Processes which were important to the formation of our solar system are also important in star formation, and galaxy evolution, so we will be visiting many of these concepts again. Procedure Part 1: Shapes of Planetary Orbits Figure 1: The orbits of the inner planets Figure 2: The orbits of the outer planets1. Examine Figure 1, which shows the orbits of the inner planets. In general, what shape are the inner planet orbits? 2. Are all the orbits centered in the same place? Which two orbits are most off-center? Are these also the most elliptical (least round) of the orbits? 3. Examine Figure 2, which shows the orbits of the outer planets. In general, what shape are the outer planet orbits? 4. Which of the planet orbits is different from the others? What are two ways in which the odd orbit is different from the others? 5. In one sentence, describe the shapes of the orbits of the planets. Part 2: Inclinations of Planetary Orbits Inclination = If you drew a straight line from the sun through Earth, inclination is the angle of other planets’ orbits above or below that of Earth’s (so Earth’s inclination = 0)TABLE 1: Rotation and Revolution DataPlanet Planet RevolutionAppx. Inclination of Orbit Planet Rotation Moon Revolution Planet Density Mercury CCW 7CCW No moons 5.4 Venus CCW 3CW No moons 5.2 Earth CCW 0 CCW CCW 5.5 Mars CCW 2CCW CCW 3.9 Jupiter CCW 1 CCW CCW 1.3 Saturn CCW 2CCW CCW 0.7 Uranus CCW 1CCW CCW 1.3 Neptune CCW 2 CCW CCW 1.6 Pluto CCW 17CCW CCW 2.1 1. Examine Table 1. Which object has the largest inclination?2. In general, how do the inclinations of the Inner Planets compare with those of the Outer Planets (don’t forget that Pluto isn’t a planet)3. Why is the Earth's inclination exactly 0? 4. In one sentence, describe the shape of the solar system, using your answers from Part 1 and Part 2. Part 3: Rotations of the Planets 1. Examine Table 1. In which direction is our solar system rotating and revolving? 2. Which planet is not rotating the same direction? 3. Do the rotations of solar system bodies seem to indicate that most of them formed 1) together at the same time in the same way, or 2) separately under different conditions? 4. How could you tell if a moon or planet did not form with the rest? If a moon or planet did not form with all the others in its vicinity, how might it have gotten there? Part 4: The Densities of Planets 1. Examine Table 1. Compare the densities of the inner planets and outer planets. 2. Where in the solar system would you expect to find most of the iron and radioactive materials (the heavy stuff!)---1) the inner or 2) outer solar system? Part 5: The Standard Model In the standard model of the formation of the solar system, we begin with an enormous cloud of gas and dust (solar nebula), which is slowly rotating counterclockwise. Because there is mass in this cloud, it begins to collapse under gravity. This spinning cloud has angular momentum (like and ice skater), and so as it collapses, it must spin more rapidly. During this time, the particles can slip past each other easily, since the cloud is not very dense. The heavier particles, like iron and uranium, are more strongly attracted towards the center, and so the fraction of heavy atoms becomes higher near the center of the cloud. As the cloud collapses, it becomes denser. Eventually, it becomes dense enough for particles to begin to collide, and sometimes stick together, forming larger particles. This is called condensation. These larger particles are orbiting the center of the cloud counterclockwise, because the smaller particles were traveling in that direction. As these larger particles begin to collide with other particles of the same size, they 'regularize' the orbits. That is, the collisions with particles moving slightly outward in their orbits are as common as collisions with particles moving slightly inward in their orbits, causing the orbit of the growing body to become more and more circular, and less elliptical. Similarly, particles which are traveling north are as common as those going south. As these particles collide, their velocities average out, causing the cloud to flatten into a disk. The cloud continues to collapse because of gravity, and to spin faster because of the conservation of angular momentum. Larger and larger particles form, which are rotating and orbiting counterclockwise, just like the original cloud. Eventually, most of the large particles have been gathered up into a few large bodies, and continue adding mass by running into lots of smaller particles. This is called accretion. We have now accounted for the shape of the orbits, the shape of the solar system, the rotations of the planets, and the distribution of densities. All with a very simple model of a cloud which collapses under gravity, and conserves angular momentum. As you will find out later in the term, however, this is far from the whole story. It works pretty well for our solar system, but fails when applied to the dozens of planets around other stars which have been discovered in the last decade. 1. What is the difference between condensation and accretion? 2. What would happen if the cloud were so thin that gravity didn’t affect it? 3. How does angular momentum help the solar nebula form into a solar system? Extension Questions:1. How might you explain Venus' counter-rotation? Feel free to engage in wild speculation. This is an unanswered question in astronomy! 2. How might you explain the oddities of Pluto's orbit? Can you see why Pluto's status as a planet is disputed by many astronomers? ................
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