Chapter 7

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University of Toronto St. George
Astronomy & Astrophysics
Clifford Orwin

Chapter 7: Our Planetary System Oct192010 7.1 Studying the Solar System Comparative Planetology: The study of the solar system by examining and understanding the similarities and differences among worlds. The essence of comparative Planetology lies in idea that we can learn more about individual world, including Earth, by studying it in context of other objects in solar system. Four Major Clues As To How Solar System Formed: (1) Large bodies in the solar system have orderly motions (2) Planets fall into two major categories [1] small, rocky, terrestrial planets [2] large, hydrogen-rich jovian planets i.e. Uranus, Saturn (3) Swarms of asteroids and comets populate the solar system in the asteroid belt [btw. Mars and Jupiter], the Kuiper Belt [beyond Neptunes orbit], and Oort Cloud [spherical region in distant solar system encompassing Kuiper and Asteroid Belts.] (4) Several notable exceptions to the above stated trends stand out Ex. Uranus unusual axis tilts. The Sun Radius: 696,000 km = 108R Earth Mass: 333,000M Earth Composition (by mass): 98% hydrogen and helium, 2% other elements. More than a thousand times as massive as everything else in solar system combined. Roiling sea of hot (apprx. 5800K, or 5500 degrees Celsius) hydrogen and helium gas. Surface is speckled with sunspots that are slightly cooler than their surroundings. Fusion transforms 600 million tons of Suns hydrogen into 596 million tons o He. Missing 4 million is converted into energy according to E = mc .2 Gravity governs orbits of other planets. Heat is primary influence on temps o planetary surfaces and atmosphere. Charged particles flowing outward from Sun (Solar wind) help shape planetary magnetic field and can influence planetary atmospheres. Mercury Average distance from the sun: 0.39 AU Radius: 2440 km = 0.38R Earth Mass: 0.055M Earth Composition: Rocks, metals Average Surface Temperatures: 700 K (day), 100 K (night) Moons: 0 Smallest of eight official planets Desolate, cratered world with no active volcanoes, no wind, no rain, and no life. Rotates once every 58.6 days Rotates exactly three times for every two of its 87.9 day orbits of the Sun. Shows evidence of past geological activity Plains created by ancient lava flows and tall, steep cliffs that run hundreds of km in length. These cliffs, though, may be wrinkles from an episode of planetary shrinking. Mercurys high density indicates that it has an iron core. Venus Av dist from sun: 0.72 AU Radius: 6051 km = 0.95R Earth Mass: 0.82M Earth Composition: Rocks, metals Average Surface Temp: 740 K Moons: 0
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