Chapter 3 Book Notes

• at least when we are looking for habitable

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Unformatted text preview: • At least when we are looking for habitable planets in other star systems, we should concentrate on finding planets that are likely to be terrestrial in character • Dwarf planets: objects large enough for their own gravity to make them round and as small bodies if they are low enough in mass to take any other shape • Asteroids: metal and rock; Comets: rock and ice • Asteroid belt lies between orbits of Mars and Jupiter; too little to count as planet itself • Kuiper belt: occupies the region of the solar system beyond Neptune in which we find both Pluto and Eris, as well as many similar objects • Oort cloud: much more distant, spherically shaped region • Kuiper belt objects • Asteroids and comets occasionally crash into planets, and these collisions can have a profound effect on any living organisms that inhabit the planet at the time • Terrestrial planets have few moons, Jovian planets have MANY moons • Conclusion: Large moons around Jovian planets offer a second category of potentially habitable worlds. Why do worlds come in different types? • Nebular theory: named because it starts with the idea that our solar system was born from the gravitational collapse of an interstellar cloud, or nebula, of gas and dust • The particular cloud that gave birth to our own solar system is usually called the solar nebula • Cloud becomes hottest near center, where Sun formed • Heating was a consequence of the law of conservation of energy • Cloud began with a great deal of gravitational potential energy---energy that it had due to its particles being far from the cloud center • Spin of cloud was a result of conservation of angular momentum • Planet formation process began when tiny solid particles condensed from the gas • Solid particles gradually grew larger though accretion • As particles grew in mass, gravity began to aid the process of their sticking together, accelerating their growth into boulders large enough to count as planetesimals , which means “pieces of planets” • Young Sun had a strong solar wind consisting of particles blown off its surface and out into space • Clearing of the gas sealed the compositional fate of the planets • Planets all orbit Sun in same direction and nearly same plane because they were born in a flattened, spinning disk • Circular orbit • Oort cloud comets may have originated as comets orbiting among Jovian planets • Conclusion: Terrestrial planets, Jovian planets, asteroids, asteroid belt, comets, Kuiper belt, and Oort cloud. Should we expect habitable worlds to be common? • Most stars are surrounded by spinning disks like that in which planets of our own solar system were born • Expect habitable terrestrial planets and habitable jovian moons • Conclusion: It seems almost inevitable that our galaxy contains many worlds that have liquid water and hence would seem to make suitable homes for life....
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• At least when we are looking for habitable planets in...

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