Chapter 7 - Studying the Solar Sytem Notes

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Astronomy & Astrophysics
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Michael Reid

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Notes – Our Planetary System 7.1 Studying the Solar System - Galileo’s telescopic observations sparked a new era in which the Sun, Moon and planets could be studied as worlds rather than just mere lights - We can study these worlds individually - Comparative Planetology: We also study these worlds by comparing one to another (this term is used by astronomers broadly as it includes moons, asteroid, comets and planets) What does the solar system look like? - The planets are all quite small compared to the distance between them - All the planets in our solar system orbit the sun in the same direction: pattern What can we learn by comparing the planets to one another? - By studying a planet in the context of other objects in the solar system, we are able to learn more about that individual world. Analogy: getting to know a person by learning more about their culture, family, friends Advantages of comparing Planets: 1. Comparative study has revealed differences and similarities – helping guide the development of our theory of the solar system 2. New insights into the physical processes that have shaped Earth and other worlds 3. Allowed us to apply lessons we’ve learnt from our solar system to the study of other planetary systems : may help lead us to discovering where other Earth-like planets exist Cosmic Context Figure 7.1 1. Large bodies in the solar system have orderly motions – all planet s have nearly circular orbits going in the same direction on the same plane 2. Planets fall into 2 categories: Terrestrial planets - Small in mass and size - Close to the Sun - Made of metal and rock - Few moons and no rings Jovian Planets - Large mass and size - Far from the sun - Made of H, He, and hydrogen compounds - Rings and many moons 3. Swarms of rocky asteroids and icy comets populate the solar system - They are mainly found however in 3 distinct regions  Asteroid Belt: find asteroids (made of metal and rock) in orbit between Mars and Jupiter  Kuiper Belt: comets (ice rich) found beyond Neptune’s orbit  Oort Cloud: more comets orbit the sun in this outer region, rarely do they plunge into the inner solar system 4. Several unusual trends stand out - Earths unusually large moon - Uranus’ odd tilt (rotates on its side compare to its orbit) The Sun - Contains more than 99.8% of the entire mass in our solar system (largest & brightest in s.s) - Sunspots are each large enough to swallow several earths – sunspots are slightly cooler than their surroundings - Solar storms: steamers of hot gas soaring above the surface Radius: 696, 000 km= 108 R Earth Mass: 333,000M Earth Composition (by mass): 98%hydrogen and helium, 2% other - Gaseous - In its core lies the Sun’s energy: temperatures and pressures are so high that there exists a nuclear fusion power plant - Each second this fusion transforms 600 million tons of the Sun’s hydrogen into 596 million tons of helium - The mission 4 million become energy (Einstein Emc2) - The Sun’s gravety governs the orbits of the planet - It is the source of nearly all the light in our solar system - The solar wind (charged particles flowing outward from the sun) shape planetary magnetic fields and influence planetary atmospheres. Mercury Distance from Sun: 0.39 AU Radius: 2440 km= 0.38R Earth Mass: 0.055M Earth Average Density: 5.43 g/cm3 Composition: rocks, metals – surface heavily crated Average Surface Temperature: 700 K (day) 100 K (night) Moons: 0 - Closest to earth, smallest - Desolate: no volcanoes, wind, rain, no life - No air to scatter sunlight: stars visible during the day - World of both cold and hot extremes - Tidal forces form the sun have forces Mercury in an unusual rotation pattern - Mercury has days and nights which last about 3 months each - Temperatures are also drastically different during the night and day due to its 58.6 day rotation period: meaning it rotates exactly three times for every two of its 87.9 day orbits of the sun - Shows evidence of past geological activity: ancient lava flows, steep hills - Very large iron core (perhaps due to suffering a huge impact that blasted its outer core) - Has frozen water – tiny quantities Venus Distance from Sun: 0.72 AU Radius: 6051 km= 0.95R Earth Mass: 0.82M Earth Average Density: 5.24 g/cm3 Composition: rocks, metals Average Surface Temperature: 740 K Moons: 0 - Second planet from the sun – identical size to earth - Rotates on its axis slowly, opposite direction as the earth – days and nights are very long - Surface is hidden by dense clouds - Mountains, valleys, craters, evidence of past volcanoes - Venus resembles a traditional view of hell - An extreme greenhouse effect bakes Venus’ surface to an incredible (880F), the thick atmosphere also creates immense pressure - Contrary to popular beliefs, Venus is NOT a sister planet to Earth - Venus’s greenhouse effect is cause by carbon dioxide – same gas that is responsible for global warming on Earth - Perhaps further understanding Venus will allow us to understand and solve some of Earths problems? Earth Distance from Sun: 1.00 AU Radius: 6378 km= 1R Earth Mass: 1.00M Earth Average Density: 5.52 g/cm3 Composition: rocks, metals Average Surface Temperature: 290 K Moons: 1 - Only known oasis of life in our solar system - Only planet with oxygen, ozone to shield from solar radiation and abundant surface water to nurture life - Atmosphere contains sufficient carbon dioxide to maintain moderate greenhouse effect = pleasant temperatures - Planet closest to the sun to have a moon - Hypothesis regarding Earth’s moon: it formed as a result of a giant impact early in Earth’s history Mars Distance from Sun: 1.52 AU Radius: 3397 km= 0.53R Earth Mass: 0.11M Earth Average Density: 3.93 g/cm3 Composition: rocks, metals Average Surface Temperature: 220 K Moons: 2 (very small) Phobos and Deimos - Last of the four inner planets of our solar system - Larger than Mercury and the Moon but only half Earth’s size - Although Mars is frozen today, its dried-up riverbeds, floodplains and minerals that form in water prove there were at least some warn and wet periods in the past - Some liquid water could persist underground - Mars’s surface looks Earthlike - Disadvantages: air pressure is low, temperature below freezing, scarce amounts of oxygen, lack of atmospheric ozone (exposed to ultraviolet radiations) - Big plans for Mars : including sending humans Jupiter Distance from Sun: 5.20 AU Radius: 71,492 km= 11.2R Earth Mass: 318M Earth Average Density: 1.33 g/cm3 Composition: mostly hydrogen and helium Cloud Top
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